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LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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EQUIPMENT : LOAD COMMUTATED INVERTER (VFD)
DOCUMENT : COMPENDIUM OF FAULTS/ALARMS
DOCUMENT NO. : 441/COMPEND/LCI REV.054 DTD.30/0812/0607
When referring to a solution for a problem, the particular category of
Fault /Alarm is to be seen. Further please also read General checks,
Checks for ground fault, Load Commutation Failure, Load PLL Fault and
SEM Earthing document at the end of this document.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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REVISION HISTORY SHEET
NATURE OF CHANGE
REV.NO./ DATE PREPARED BY CHECKED BY APPROVED BY
FIRST ISSUE
UPDATED UPTO 09.06.04
UPDATED UPTO 10.03.05
UPDATED UPTO 30.08.05
UPDATED UPTO 30.08.06
UPDATED UPTO 30.12.07
00 /25.03.04
01 /09.06.04
02 /10.03.05
03 /30.08.05
04 /30.08.06
05 /30.12.07
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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Category Sl.no. Problem Solution MISC 1. Small crack observed in base of 1 no. CT in Load
Break Switch Panel.
Failure of CTs.
The primary connections on the CTs are such that load of
the Cu bars is coming on the CTs. Therefore necessary to
provide flexible connection on one side of the CT.
Customer opined that failure may be due to thermal
stresses.
This point was taken care of when replacement of Load
Break Switch with Contactor was done.
MISC 2. Gaskets on doors have gaps at many places resulting
in air being sucked through these gaps also.
Customer opined that replacement of gaskets necessary.
Gaskets replaced at places wherever required.
MMI FOR VFD 3. MMI remains out of service due to “Communication
Link failure”.
MMI s/w hanging problem.
Defective line driver replaced by a new one.
Demultiplexer channels at control room were not working.
Same repaired.
One wire of RS232 port was found disconnected, same
rectified.
One reed relay card to be replaced (failed during
troubleshooting). MMI system put on-line bypassing Drive
status and Reset command from PC.
Replaced reed relay card. Problem solved.
Corrected version of software installed. Became OK.
MISC 4. 6A Ch-2 tripped on electrical fault.
Current hunting was observed in Ch-1 and tripped on
R phase Overcurrent.
When Ch-2 of ID Fan 6A trips, current/voltage
hunting is observed in the Ch-1 and it also trips.
Motor foundation vibration found higher compared
to other motors.
1. “LMARG” changed from 25° to 30°. No change
observed.
2. “FLALEN” and “FLASEN” changed to TRUE. No
change observed.
3. Changed parameters “CRGAIN, FRGAIN, FRTC,
PLLTOL, LIMARG”. No change observed.
4. Finally by changing PLLMODE from 60 to 25, problem
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was solved.
SHORTED
MOTOR
WINDING
5. 6A Ch-2 trips with message “Shorted motor
winding.” Ch–1 stopped after current hunting
observed.
However, current drawn continues to be higher than
other fans due to poor p.f.
NLCB card in Ch-2 found defective. Card replaced and
problem solved.
MISC 6. Tripping of channels due to Loose connections of
cards on SEM rack.
Proposal for installing Anti-vibration pads on blower
support in panel. Concurrence given by BHEL for the
same.
Anti-vibration pads put and SEM lock bars installed.
Problem solved.
MISC 7. Frequent failure of NPPB card. Heat dissipated by
bleeder res. is high. Bleeder resistor installed on
PSFF just behind mother board NPPB.
Proposal by customer to install bleeder resistor outside
PSFF module.
Customer asked to check VFD room temperature and clean
the mesh filter on C&EXE panel. Bleeder resistor can be
mounted outside only if above remedies do not work.
Temperature in VFD Room rectified. Problem solved.
MISC 8. Self Test halts at No.23 even though channel is
healthy.
BHEL requested customer to furnish a print-out of self
test program to study the problem.
Customer asked to adjust offset zero on NLIB load card
FAB, FBC & FCA with BAL1 and BAL2 pots on NLCB
Allowed tolerance is 30mV. Problem solved.
MISC 9. UPS supply tripping on trf. inrush current.
120/120VAC, 1ph, trf. with 2P & 2S windings, 1 sec.
Winding found defective.
Spec. for trf. given by EDN to TEC with msg. to procure
trf. locally. Screen to be provided between primary and
Sec. of trf. and Screen to be earthed to panel frame.
Changed transformer. Problem solved.
MISC 10. 6A Ch-1 tripped , Ch-2 not responding to speed
lower command from CRT. Current and speed of ID
fan stuck. 6A taken out of service manually and 6B
taken into service. SRCLSC found to be 0.7 instead
of 1.0 in other channels.
Parameter SRCLSC changed to 1.0 as in scheme.
4-20mA speed signal is not being recd. by Ch-1 or Ch-2.
Problem in I&C system solved. 6A taken into service.
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MISC 11. Erosion of cooling tubes at the tip of the
tubeshoot at O/B side of ID Fan motors. Resulted
in passing of external air into motor body. Motor is
CACA cooled.
Customer proposed to replace all cooling tubes (1980
tubes). Asked for advise.
Referred to contact BHEL/EMRP-Mumbai for further
action.
MISC 12. ID 6A Ch1 – oscillating and load currents on
contactor not balanced. 1 phase current missing.
Source currents balanced. 0IA load NLIB
negative humps missing.
Told to change HPTF card in LTM1 or LTM4.
Pulse was missing in LTM4. Changed HPTF card. Problem
solved.
MISC 13. Repeated faults in drive due to loose connection on
SEM Rack.
Recommended to install lock bars to secure control cards
in the racks. SEM Lock bar installed. Problem solved.
MMI FOR VFD 14. MMI getting hung frequently. Line drivers OK.
After PC rebooting the MMI PC, communication
gets re-established.
If power goes OFF, sometimes MMI PC hangs as told by
customer. EDN suggested to put the MMI PC on UPS so
that this will not occur. MMI put on UPS. Problem solved.
MISC 15. ID Fan 6A taking high current (400A), current of
both channels hunts in the range 320-400A.
Higher current is due to higher LMARG and LIMARG as
motor p.f is lower. Adjusted SRGAIN such that hunting of
speed and current stops. Problem solved.
LOAD PLL FAULT 16. 6C1 tripping on “Load PLL fault”. Gate test OK. Self
test OK upto 40. Channel goes back to service
every time after tripping.
Additional to Load PLL fault, MP alarm also coming.
IMOK of HMPG and NLCB missing. Missing Leds
come on after reset.
6C1 started as slave channel after swapping HMPG
with 6C2. Load current does not come immediately
but hunts a lot. Also LED ‘0’ on HRDA card (for
MAMS) flickers. Firing of load thyristors also
flickers. Flickering stops after sometime and
channel becomes OK. Channel trips after few days.
HRDA, HROA, NLCB replaced. NLIB Source & Load
replaced.
Tripping freq. increased.
EDN Suggested
1. To install lock bar of SEM. HMPG/DMPB may be loose
in its slot.
2. Clean HMPG/DMPB and pins on mother board by air
blowing.
Load current hunting may be due to MTRFMIN and FLUXS
values being slightly different than actual requirement.
Suggested to lower the values of MTRFMIN and FLUXS in
steps of 0.01 and if not sufficient again in steps of 0.05.
Problem may be due to slight drift of NLIB load side flux
calibration over the years of service.
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Also asked to check SEM earthing as per SEM Earthing
document. Problem solved by adjusting offset zero to less
than 30mV on NLIB using source volts and also earthing
SEM as per document.
LOAD PLL FAULT 17. 6C1- Trips on Load PLL Fault on load. Increased LMARG from 20° to 25°.
Problem solved.
SOURCE
OVERCURRENT &
LOAD
OVERCURRENT
18. After starting the channel, as soon as current and
voltage started building up, channel tripped on
Source Overcurrent, Load Overcurrent and
Microprocessor Alarm.
On taking trial, current and speed developed OK.
On reaching 90-100rpm, channel tripped again on
Microprocessor alarm. LBS O/C relay operated,
Lock out of Source breaker operated and tripped
the breaker. IMOK LEDs of HMPG and NLCB not
glowing.
Firing cards on all thyristor legs of Source and Load side
were checked. Found that jack plug on one of the source
side cards was not fixed properly. Same rectified and
plugs of all cards were thoroughly checked.
All cards removed and cleaned and checked for any
abnormal marks or heating on the cards. Found OK. Dust
accumulation was completely removed. Channel trial taken
and found OK. Changeover trials taken for both the
channels and found OK. Fan taken into service.
MISC
REV.04
19. Severe hunting of currents in Master and Slave
channels when speed is brought to near minimum
speed.
ID Fan functions normally during service when unit is
generating full load. Also all the waveforms of voltages and
currents in both channels found OK. Found that rubber
blocks in the coupling had deteriorated. Rubber blocks
changed. Problem solved.
SOURCE
UNDERVOLTAGE
R05, 0207, VI
20. Current hunting over a certain speed. At this time,
INVLIM sets to 384 (256+128). 256=STOP,
128=SOURCE UNDERVOLTAGE. Boiler under
shutdown.
Shorted LBKRS TBs on IOMA (Source breaker input).
Problem persisted. Checked Earthing of SEM and panel.
Found OK. Since boiler was under shutdown, channel run
independently. Found that the hunting problem was related
to current and not to voltage.
Changed HLCB, NLIB Source, NSFC source. Problem still
persisted. All waveforms of current, flux, voltages found
OK. CT phasing on Source side OK. Found that NLIB
Source and NLIB load were interchanged. As the
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compensation resistance for reactances are different in
DLIB Source and Load, this was giving rise to wrong
position of interrupts on HLCB during higher currents.
Wrong interrupt position was causing very high current for
extremely short duration, giving rise to Source
undervoltage. Swapped the Source and Load DLIB cards.
Channel taken into service. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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Category Sl.no. Problem Solution LOAD
COMMUTATION
FAILURE
1. Channel trips on Load Commutation failure 1. HPTF card in LTM3 found faulty when doing crowbar
test. HTPF card replaced. Problem solved.
2. BHEL has suggested to maintain control room
temperature at 25°C.
MISC
2. 1 no. motor burnt out.
Replaced by spare motor available at site. All tests
while taking new motor into service done by
customer with telephone support from BHEL-EDN.
Lead from stator was found melted out. Connections were
wrongly crimped. Connections Brazed and motor ready.
Kept ready for service.
LOAD
OVERCURRENT
3. Channel tripping once a week with message “Load
Overcurrent”. 2 out of 3 flags in VFD Overcurrent
Relay have operated. Channel starts after resetting
and starting.
Suggested to
1. Operate Overcurrent relay manually and check for
same message print-out on printer.
2. Short the relay contact which is in series with load
contactor aux. contact going to IOMA.
3. Change Load NSFC card.
NSFC load card was changed and problem solved.
LOAD
COMMUTATION
FAILURE &
SHORTED
MOTOR WINDING
4. Channel tripping with fault message “Load
Commutation failure” and “Shorted motor winding”
Firing pulse LED on one card in source bridge
(HPTF) was not steady and was flickering.
Suggested to
1. Change NSFC load card
2. Checking of all connectors and RC filter circuits on
load side.
3. Check power bridge on load side.
HTPF card on source side changed and problem solved.
GROUND FAULT 5. Ground fault in both channels of 4B. In one channel one load side capacitor was faulty. In the
other channel, the neutral grounding of R-C circuit was
not OK. Problem in both channels solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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MISC 6. Chattering of MAMS relay in slave channel. Adjusted offset zero in NLIB Load FAB,FBC,FCA by back
charging from Master. Problem solved.
MISC 7. HMPGDMPB in 4B1 giving Bushog after few hours
in service.
HMPG/DMPB card replaced.
Problem solved.
GROUND FAULT 8. VFD Ground Fault problem in slave channel. See text on ground fault at the end of this document.
Cable insulation was found faulty on cable from contactor
to motor during hi-pot test to earth. Problem solved.
MISC 9. Master and Slave both start and run individually. At
minimum speed, slave does not take load when
paralleled with Master channel.
Back-charged slave with source breaker open and load
Contactor closed. Adjusted FAB, FBC, FCA on NLIB-load
on slave with that of Master.
Slave channel paralleled. OK. Problem solved.
MISC 10. Ch-1 tripped but no annunciation on the door
mounted printer or at remote C&I.
Initially suspected that "Stop" command was being issued
from C&I system, but found this was not true. Channel
selector switch and Local/Remote switch on IOMA were
bypassed but trippings continued. Trippings were reported
at regular intervals.
Laptop PC was then connected to HMPG. Found that
Microprocessor was getting reset every time the drive
tripped. This was evident from the Laptop display.
This could happen only if LVSH from PSFF goes "High".
PSFF supply was cleaned by blowing air. Channel put into
service and no trippings observed.
PSFF changed as per customer requirement. No further
trippings observed.
MISC 11. 1. After overhauling, when ID Fan-B was started, it
became ON & OFF many times on its own. When fan
speed was increased, it became normal. Again when
the channel was started after station tripping, same
problem occurred. 2. When Ch-2 was started,
Drive received ON command and took load also, but
Problem is that Ch-2 is not going to LMODE=3. The
reason is that the flux levels in the machine is lesser than
the values set for FLUXS and MTRFMIN.
Following suggested:
During the next shutdown, backcharge Ch-2 and adjust
NLIB Load Flux values to the same as in Ch-1. Also please
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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OFF status did not go from the desk, while RUN
indication was appearing on the VFD panel. Then,
Ch-1 was started first and Ch-2 started
thereafter. Now drive started normally.
check the FLUXS, MTRFMIN and FRSTART values in Ch-2
are the same as in Ch-1.
Start motor from Ch-2 and please check motor goes to
LMODE=3.
SPD and SPM pots on NLCB do not matter for proper
starting of the drive.
SHORTED MOTOR
WINDING
12. Ch-1 tripped on Shorted Motor Winding. Ch-2 made Master and Ch-1 Slave. Adjusted Load flux in
NLIB Load in Ch-1 same as in Ch-2. Channel taken into
service. Problem solved.
LOAD
COMMUTATION
FAILURE
R05, 0807, PH
13. Channel trips on Load Commutation failure as soon
as it is paralleled.
Invoked Gate test and found that 1 no. LED on HPTF Load
side Pulse transformer card was not glowing. Replaced card
and re-checked under Gate test mode. LED glowing OK.
Channel taken into service. OK.
LOAD
COMMUTATION
FAILURE
R05, 1007, PH
14. Master channel is running. When Slave is paralleled
to Master, current in Slave is not same as in Master.
Further Slave channel sometimes trips on Load
Commutation failure.
When currents are steady in both Master and Slave,
CRSTART values were checked with Laptop PC and found
to be different. Further in Master Channel, other channel
running signal IOMA TB5/09,10 was TRUE. Also, the
current reference from Master channel IOMA TB7/10,11
was positive which is OK for motoring. Therefore, fault
was in Slave (Ch-2). Changed NLCB card as this is the first
card in the signal path for current reference. Paralleled
Slave Ch-2 to Master. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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Category Sl.no. Problem Solution MISC 1. During Start-up operation, ID Fan has tripped on
“Source Overcurrent” on channel Ch-1 and Load
Overcurrent” on channel Ch-2. Overcurrent relays
operated on load breaker switch.
Restarted the drive but again tripped on the same
fault. LMODE on HHT not changed from ‘0’.
1. Conducted all tests-found OK. Run in Local mode and
motor in uncoupled condition. OK.
Motor coupled back and started drive with slightly
higher CRSTART & FRSTART. Motor start and run was
OK from both channels. Normalised CRSTART &
FRSTART to original values.
This phenomenon happens after long shut down, when
oil film under fan bearing not built-up or inlet damper,
inlet and outlet gates not properly closed during start.
Customer has been asked to check these points.
MISC 2. Channel tripping several times due to various faults. Customer feels that mother board is not giving proper
contact to SEM modules which causes frequent trips. Has
requested to change all mother boards or provide
alternative modified female connectors in mother board.
BHEL-EDN sent SEM lock bars to customer and the same
was installed on all SEM modules. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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Category Sl.no. Problem Solution MISC 1. ID Fan 6A suddenly got unloaded even though motor
contactors are ON. ID Fan 6A currents suddenly
dropped to zero.
FD Fan 6A did not trip on interlock ID Fan 6A
Speed<Min.
Both fans were hand tripped, restarted.
ID Fan 6A hand tripped and FD Fan 6A tripped on
“ID Fan Speed <Min”.
220 VDC supply from distribution board failed and
therefore contactor did not trip. Further STOP command
was issued from I&C to both channels as 220V DC supply
had failed.
Further customer asked to check in I&C system whether
MAMS has been taken for MFT1, MFT2, MFT3 in FSSS
for ID Fan OFF. Customer confirmed that same has been
done.
PLL FAULT 2. Channel tripping frequently on “PLL Fault”. After
manual reset, channel comes into service.
SEM not earthed properly. SEM earthing done as per SEM
Earthing document. Problem solved.
GROUND FAULT 3. Slave channel tripped on Ground Fault.
Flex leads at motor terminal box had got melted and
neutral point on bushing was burnt out. Motor stopped,
rectification done by putting HT Insulation tape.
MISC 4. Fan started from standstill and did not start. Fan
did not pick up speed and was rotating very slowly in
the wrong direction..
Suspected No flux build up possibly because of melting of
field lead connections inside motor rotor exciter.
STIM, FRSTART, CRSTART increased. Motor Started.
Parameters changed to old values and start trials taken
were successful. Old parameters retained.
Reason- High breakaway torque. Subsequent starts were
OK because oil film was formed between bearing metal &
shaft, causing lower breakaway torque.
LOAD
COMMUTATION
FAILURE
5. 5A2 channel tripped on ”Load Commutation failure Found thyristor in leg module LTM3 defective. Both
thyristors were shorted out. Replaced leg module. Problem
solved.
FAILURE TO
START
6. 6A Ch-1 started, LMODE did not increase from ‘1’
many times in spite of changing parameters like
MTRFMIN, FLUXS, STIM, CRSTART, FRSTART
etc. Suspected motor winding may be faulty.
Found that snubber in STM6 was faulty. Capacitor was
shorted. Replaced snubber. Problem solved.
Customer asked to check bearing alignment on Fan bearing
in next shutdown.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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Connected Ch-2 winding of motor to Ch-1 of LCI.
Problem persists.
LOAD
COMMUTATION
FAILURE
7. Channel tripping on “Load Commutation Failure” in
5B1 and “PLL Fault” in 6A1.
HPTF cards changed in both channels after doing crowbar.
SEM earthing done as per SEM Earthing document.
Problem solved.
MISC 8. There was a heavy jerk on grid and due to that
almost all 210MW units tripped out. When starting
and taking ID Fans on load, found that Fan B was not
taking load, but Fan A was getting loaded. Currents
and voltages in both channels equal in Fan B. This
phenomenon was present even when Fan B was run at
700 rpm.
Changed Slave to Master and vice versa. Problem persists.
This confirmed no problem in VFD. Found problem was in
Inlet damper to ID Fan. Damper was almost in closed
condition and would not open. Corrected damper problem.
Problem solved. OK.
MISC 9. When Ch-2 is individually started, Load contactor
closes, Field contactor closes but no current in
motor. But Ch-2 (Slave) can be paralleled with Ch-
1(Master) and is OK. If Ch-1 is tripped, then Ch-2
does not take the load and its current stays at zero.
FLDCN (Field Contactor close) was not true in Ch-2 when
running alone. Aux. contact of Field contactor was not OK.
Rectified. Problem solved.
MISC 10. Top mounted blower (one of the two) on the
synchronous motor was giving lot of sound and
needed replacement.
Load was reduced to 150MW by lowering the speed and
also the channel currents. The temperature of windings
dropped by 10 deg.C. Blower replaced and then vent load
raised. No rise in temperature of windings during change
of blowers. Problem solved.
Caution: It was advised to keep monitoring the winding
temperatures during the change and trip the motor if
winding temperature exceeded 120 deg.C. It must be
noted that there is no part load rating of the motor with
one blower of the two out of service. This is due to the
inherent construction of the heat exchanger and mounting
of blowers in the heat exchanger.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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MISC
R05, 1006, PH
11. Drive end bearing problem. Excessive vibration. Decision taken to change motor. Motor replaced and
following tests conducted on both channels:
a. Exciter test
b. Uncoupled run
c. Coupled run
The readings compared with those recorded during
commissioning/annual overhaul, especially observing the
readings of exciter voltage and exciter current for Sl.b
and c. All readings found in order. Fan taken into service
with new motor.
Formatted: Bullets and Numbering
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Category Sl.no. Problem Solution MISC 1. 1. Channel B2 tripped on “Motor Isolator not
closed.”
2. Second time tripped.
1. Breaker closing link was not latching and breaker was
tripping immediately after closing (Mechanical
problem). Breaker truck replaced and channel started.
Found that latching mechanism was faulty. Faulty part
replaced and CB truck tested and kept ready for
service. Problem solved.
2. Fault resetted and started.
LOAD
COMMUTATION
FAILURE
2. Channel B1 tripped on “Load Commutation Failure” 1. Checked load bridge capacitances for charging
currents with megger – OK..
2. Checked MOVs of load bridge for Insulation
resistance.- OK.
3. Checked gate pulses on HPTK card in gate test mode.
One HPTK card pulse not OK. Replaced card. Problem
solved.
MISC 3. “Bus hog “ error on HMPG card. Inserted HMPG card properly.
Put lock bars on SEM rack.
Also checked whether EPROMS are inserted properly on
HMPG/DMPB. Problem solved.
SOURCE
UNDERVOLTAGE
4. Tripping on “Source Undervoltage when BFP started
and during fast bus changeover from unit to station.
Source Undervoltage alarm appears immediately but
“Source Low line” fault appears after sometime.
It was observed that source voltage dips below u/v set
value whenever MDBFP starts. This is because of very high
Inrush current in MDBFP. Changed source u/v setting to a
lower value as per site requirement. Problem solved.
MISC 5. Abnormal sound of blower in panel. Due to damaged bearing of fan.
Bearing changed and fan replaced. Problem solved.
MISC 6. 2 nos. temp. scanners are malfunctioning. Hence
tripping removed. However, winding temp. and
bearing temp. tripping from I/C panel is in service.
BHEL agreed to repair the faulty scanners. Scanners sent
to BHEL-EDN for repair.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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MISC 7. Speed indicating at VFD panel and actual speed are
matching. Speed at PMS not matching.
BHEL has requested to adjust the mA reading as per
procedure given in VFD O&M manual, Vol1-Book1-Chapter
Clause 6.15.4 & 5.
EDN reply-The speed signal o/p from VFD to Plant C&I is
only for Indication Purpose & not for regulation/control.
Speed feedback on all channels adjusted. Speed reading on
PMS and actual speed are matching.
COOLING
BLOWER LOSS
8. Alarm “Cooling blower loss on Ch-1 and tripped on
“Loss of cooling fan”. But blowers running normal.
Fault resetted and drive started.
Cooling blower contactor dropped. 415V UV has occurred
for a time greater than normal leading to this trip.
MISC
9. Fan tripped without any indication.
Tripped due to failure of SEM supply.
Fan tripped without any indication.
Fan tripped without any indication.
MCB of PSFF had tripped. MCB reset and made ‘ON’. PSFF
was malfunctioning in this channel.
Site concerned about momentary malfunctioning of
electronic cards since on next starts, card behaves normal.
Sometimes, no alarm is annunciated.
EDN replies that tripping of VFD channel & becoming OK
after MP reset could be due to:
a. Dust accumulation on PCBs
b. Loose connection between card & backplane connector.
All cards, Power modules, Power supplies cleaned with
blower. Problem solved.
Failure of HRIA card. Failure due to RUNX relay failure.
HRIA replaced and channel restarted.
Processor found hanged. Control supply made ON/OFF.
Processor normalised and restarted.
GROUND FAULT 10. Channel tripped on ground fault. Fault resetted and channel started smoothly. Problem may
be due to :
a. Loose connection in load side connections (busbars,
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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connector, earthing lug on HPTK, SEM Earthing.)
b. Loose connection on star point of load side filter
capacitor circuit.
c. Check voltage setting.
Site says all connections above have been found normal.
Suspected transient ground fault as there were no failures
of components to detect the same.
SOURCE
COMMUTATION
FAILURE
11. Tripped with following indication on printouts:
a. Source O/C b. Load Commutation failure c. Load
O/C d. Source commutation failure.
b. Channel could not be restarted, tripping on same
faults and hunting in currents.
1. UPS voltage at panel checked and found OK.
2. Source side thyristor STM4 found failed. Replaced
module STM4 and channel taken into service. OK.
MISC 12. ID Fan B-1 speed was locked at in running condition. HMPG found hanged. HMPG resetted and fan started.
Could be due to loose connection of HMPG.
Site advised to put lock bars on SEM. Problem solved.
SHORTED MOTOR
WINDING & LOAD
COMMUTATION
FAILURE
13. Fan B1 tripped once on a) Load commutation failure
b) Bridge filter fuse c) Shorted motor winding
Second time on a) Load Commutation Failure
Third time on a) Load Commutation Failure b)
Shorted motor winding
1. HPTK card found faulty after checking waveforms in
gate test mode. Replaced card.
2. Y ph thyristor in field exciter module had failed.
Calibration of field current feedback was wrong. Same
corrected. (in A1)
I/O PROBLEM 14. Tripped on indications:
a) Motor Isolator not closed. b) RUNP missing c)
Bridge filter fuse
Fault indications were false. Fault reset and drive
restarted. Suspected UPS feeder supply problem.
I/O PROBLEM 15. C1 tripped on
a. Source PLL Fault
b. STARTP/RUNP missing.
Fault resetted and channel restarted.
Suspected UPS feeder supply problem.
MISC 16. Channel tripped. 11kV Source breaker tripped on
IDMT O/C protection relay. No indication on VFD
before tripping.
Relay resetted and channel restarted.
Malfunctioning of IDMT relay suspected.
MISC 17. HD of 5th harmonic of VFD system is 30%. To be
confirmed.
30% HD for 5th harmonic current is acceptable as it is in
the case of all thyristor bridges. Voltage distortion is <5%
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 20 of 95
on 11kV VFD bus due to VFD operation which satisfies
requirement as per IEEE 519.
MISC 18. Channel tripped on “Circuit Breaker protection”
indication.
Investigation reveals all the thyristors in one power
module failed. Cause of the failure was that stud got
sheared. Replaced studs in all power modules wherever
failure suspected. OK.
LOAD PLL FAULT 19. Channel tripped on “Load PLL Fault Balanced Voltages at NLIB(1D) by back charging from
master channel and made voltages at FAB,FBC and FCA
equal with offset zero below 30mV DC. Channel taken into
service. OK.
MISC 20. Channel tripped with Bushog Led on HMPG Same not
resetting.
Replaced HMPGDMPB. Checked that the 6 nos. of
EPROMs are installed correctly. Problem solved.
SHORTED MOTOR
WINDING
21. Channel tripped on “Shorted Motor winding”. 1. Check thyristor healthiness.-OK.
2. Reset and restarted - tripped.
3. Dry solder in voltage attenuator circuit on XPTN
card. Attended dry solder, Self test halted at 29 &
gate test also halted. LVSH on NPSJ card in PSFF
module was not present. NPSJ replaced and restarted.
Check to be done on Berg jumper position in XPTN during
card replacement. Channel taken into service. OK.
I/O PROBLEM 22. Channel tripping on blower loss. Blower selection contact “Bottom blower selected” not
wired to IOMA card. Same done. Problem solved.
MISC 23. HMPG card did not pass Self Test. Hangs midway. Replace HMPG Put EPROMs U22, U23, U24, U25, U02, U03
and EEPROMs U04,U05 from old card in respective slots
in the new card. Lock bar to be put in SEM Rack. Problem
solved.
GATING SUPPLY
UNDERVOLTAGE
24. Tripped on Gate supply u/v. 1. In gate test mode, HPTK card in LTM1, 1A fuse blown
Replaced and started. OK.
2. MCB ‘CB2’ feeding electronic modules found tripped.
“NTRF” card in PS7 module found faulty. Replaced.
Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 21 of 95
Category Sl.no. Problem Solution SOURCE
OVERCURRENT &
LOAD
OVERCURRENT
1. Speed not raising beyond 140rpm (Rated =
700rpm). Current hunting in 2 channels.
Channel tripped on “Source and Load Suppression
Fault”
Source side attenuation voltage feedback not
available.
1. 1st channel –Current hunting due to improper voltage
feedback from source bridge due to failure of
attenuator in HPTF card. Replaced HPTF. Problem
solved.
2. 2nd channel – Wrong polarity of current feedbacks
from motor side CTs.
3. Changed NLCB card. No change observed. Original
card put back in rack.
4. Checked ribbon cable from IOMA is properly seated
on the SEM header. 4-20mA not reaching SEM.
Pressed connector & became OK.
5. Conducted crowbar test. Crowbar test OK.
Motor with both channels taken into service. OK.
MISC 2. Self test not going through. Each time test failed in
different steps.(2 racks)
0PAR signal was pulled down by defective NLIB cards.
Replaced NLIB cards in the 2 racks. Problem solved.
MISC 3. HMPG did not recognise status of running blowers
even when blowers were run. Hence Source breaker
close permissive was not available.
HMPG found defective. Replaced the 6 EPROMs from the
defective card. Ensured that they are put in the correct
position with correct polarity. Channel started. OK.
GROUND FAULT 4. Tripping on ground fault whenever speed raised
beyond 500rpm and motor volts is 500V without
any fault in motor or cable.
1. Replaced HLCB card. No change observed. Original
card put back in SEM rack.
2. 3 MOVs MOV1, MOV2 and MOV4 failed at a much
less voltage than designed.
Checked wiring in panel. Found wrong wiring. Corrected
the same. Drive taken into service. OK.
MISC 5. Cleared crowbar test. But motor not starting
smoothly. Current going to inversion.
1. Check whether CT feedback polarity is reversed on the
load side. Corrected polarity of load side CT.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 22 of 95
2. One leg of load thyristor bridge conducting. Changed
HPTF. OK.
Drive taken into service.
MISC 6. During crowbar test, one thyristor cell found not
conducting.
One thyristor found not conducting. Gate resistance found
abnormally high. Replaced thyristor cell. OK.
LOAD
COMMUTATION
FAILURE
7. Unit tripped frequently on “Load Commutation
failure causing Unit trip out.
1. UPS voltage found low, changed transformer tap to
raise the input voltage.
2. Conducted crowbar test. OK. Drive taken into service.
LOAD PLL FAULT 8. Channel tripping on Load PLL Fault. 1. Conducted crowbar test. Test was not OK.
2. Shorted DC buses on load side with DC Link Reactor in
circuit. Conducted crowbar test. Test OK.
3. Changed NSFC load and conducted crowbar test. Test
not OK.
4. Checked all thyristors and snubbers on load side
bridge. All OK.
5. Checked pulses to gate of all load side thyristors, with
current probe. OK.
6. Removed individual thyristor module on load side. Found
that tightening studs on LTM1 was loose. Tightened
the same.
7. Conducted crowbar test after removing DC bus short
on load side. Crowbar test OK.
8. Channel taken into service. OK.
NOTE: When putting back power module, pulse ribbon
cable and attenuator connector must be put in the correct
direction.
MISC 9. Channel tripped without any ‘fault’ indication and
“Bushog” LED on HMPG came ON.
Lock bar at SEM centre installed.
Checked SEM fan direction of rotation. OK.
Channel taken into service.
MISC 10. Sparking on contactor MISOL. MISOL found Cleaned contact with sandpaper and CTC and drive taken
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 23 of 95
damaged.
into service. OK.
MISC 11. VFD trips on u/v condition of control supply. VFD trf. 110V/110V given for rectification sent to site.
Customer was told to check UPS feeder voltage. Changed
tap on trf. in VFD panel C & EXE cubicle feeding
electronics. OK.
MISC 12. Reference voltage keeps varying even with constant
demand signal. Causes Drive hunting.
Motor speed and current changing at I&C, even
though steady at panel.
SPD test point gives 14V even when speed is zero.
Motor Speed and current indication at both local &
remote are erratic.
Replaced NLCB. Problem solved.
Replaced NLCB. Problem solved.
Replaced DLCB. Problem solved.
Replaced NLCB Problem solved.
MISC 13. Printer works OK in test mode, but does not print
Status/Fault from SEM
Replaced Printer. Printer sent for repair to BHEL-EDN.
I/O PROBLEM 14. HRDD does not give output LEDs and voltages
corresponding to existing status.
Replaced HRDD. Problem solved. Card sent for repair to
BHEL-EDN.
FAILURE TO
START
15. Motor crawling during starting and did not pick up
speed.
Changed parameters FRSTART, MTRFMIN and CRSTART
to slightly higher values.
Inlet and outlet gates on ID Fan duct not closed properly.
OK.
MISC 16. Channels getting unloaded with all operating
conditions normal.
Suspected due to dust accumulation on firing cards.
Firing cards cleaned by air blowing. OK.
MISC 17. Drives could not go to current limit and increase the
fan speed due to clamp on speed reference from
I&C system (Auto clamping).
Investigation to be done by customer during shutdown at
I&C system.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 24 of 95
LOAD
COMMUTATION
FAILURE
18. Channel tripping due to Load Commutation failure
Running normal after fault reset.
Loose connections in the CT feedback.
Improper earthing of SEM Rack.
SEM Rack earthed as per SEM Earthing document. Drive
taken into service. OK.
I/O PROBLEM 19. Channel tripping on Bridge Differential Pressure
fault when taken into service.
Channel started, after crossing min. speed, current
started hunting and tripped on Load Commutation
failure. Crowbar test was done for power ckt. check,
one hump missing in current waveform.
Current hunting when channel taken into service.
IOMA found faulty. Replaced IOMA.
HPTF card in source bridge found failed. Replaced and
became OK.
Load side cards not firing correctly or in sequence. One
HPTF card, both neons did not switch On/Off together.
HPTF card faulty. Replaced and Problem solved.
I/O PROBLEM 20. When RUN relay energised, BDIFSW (IOMA TB6-
08) goes high, HMPG senses this as Bridge
Differential Pressure Fault & drive trips.
To be checked in test jig of repair cell at BHEL-EDN.
Energise RUN relay in IOMA. Check if TP8 in HRIA(2A)
goes high, JJ pin 22 on SEM header goes high, flicker of
LED I15 on HISA 1B.
IOMA checked in repair cell but no fault found. Replaced
the two mother boards on IOMA. Retested and
despatched to site. Suspected tracking problem on mother
board.
MISC 21. Slave channel and Master channel can individually
start and run. But Slave channel cannot be paralleled
with Master. If paralleling is done, current in slave
remains at zero.
Backcharge Slave with Master running and adjust FAB,
FBC, FCA on NLIB Load of Slave same as Master. Use the
same multimeter.
Found Slave adjustment was not OK. Adjusted. Problem
solved.
SOURCE
UNDERVOLTAGE
22. Source Undervoltage fault even though Source
voltage is OK.
Asked to check voltage feedback circuit from HPTF
attenuator to NSFC and also line voltages on NSFC
backplane. Found Y phase Source attenuator not OK.
Replaced. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 25 of 95
Site was also asked to check whether the ground pillar on
HPTF is not loose (dry solder) before sending HPTF card
for repair.
MISC 23. Ch-1 and Ch-2 speed meters not matching. Speed meter does not have pot.
Customer advised to adjust LCI door 10V DC speed meter
after seeing counts 1024=60Hz=900rpm. Told to adjust
SPM pot only.
Problem solved.
MISC 24. Channel trips without any fault or alarm message.
RUN light is ON but channel gets unloaded
current=0.
All SEM voltages O.K.
Gate test not O.K. Self test done. Failed in test 06:
NSFC-2C. Replaced NSFC –2C. Problem solved.
MOTOR OVER
TEMPERATURE
25. System trouble annunciation appeared and Motor
Overtemperature Alarm appeared on Local panel.
Temperature scanner displayed 89 to 91 deg.C.
Similar readings found in I&C CRTs leading to
conclusion that there is an actual rise in Stator
winding temperature.
Load on channel reduced to half for about an hour and
normalised. Temperatures came down and alarm got
cleared.
Cooling blower motor found to be rotating in the reverse
direction. Direction of rotation restored to normalcy.
Temperature of motor reached a max. of 74 deg.C.
LOAD
COMMUTATION
FAILURE
R05, 1206, PH
26. Slave channel trips on Load Commutation Failure as
soon as it is paralleled with MASTER at minimum
speed. This is the first time after annual shutdown.
Back-charged Slave (Ch-2) with Ch-1 running. Found
unbalance in voltage on NSFC load. Found that attenuator
resistor LTM2 on HPTF open and 10 pin connector not
inserted properly. Changed HPTF card. Channel taken into
service. Problem solved.
LCI CHANNELS FOR VFD – COMPENDIUM OF FAULTS
Page 26 of 95
Category Sl.no. Problem Solution MISC 1. Channel starts but gives loss of speed reference
though 4mA reference is present.
Customer asked to check I&C reference. Must be 4mA
minimum.
FIELD
OVERCURRENT
2. VFD Field Overcurrent problem. Adjusted Field current feedback at SEM card. Problem
solved.
LOAD PLL FAULT 3. During starting, VFD trips on “Load PLL Fault”.
Firing pulses not getting released in Gate Test
mode even though Self test passes.
1. Variable components on NLIB-1C and 1D not as per
scheme.
2. Pin-72 of HAIA had got dislodged. Not making proper
contact on the backplane.
3. Rectified sl.no.1&2 above. Problem solved.
FIELD
OVERCURRENT
4. Channel tripping on Field Overcurrent. Checked cable of AC Input Exciter, was getting heated.
Power termination inside the module found loose.
Tightened and became OK. Drive taken into service.
I/O PROBLEM 5. HROA found malfunctioning. MAMX and ALARMX
relays remain latched even if fan is in stopped
condition & there is no alarm in the system.
HROA replaced. Drive taken into service. OK. Card sent
for repair to BHEL-EDN.
I/O PROBLEM 6. Self test Crowbar test excitation power test done
in Channel 1 & 2 of 3A.
1. 1 no. HROA card found defective in 3A1. Replaced.
2. 1 no. NSFC card replaced in 3A2.
3. Drive taken into service.
4. Cards sent for repair to BHEL-EDN.
MISC 7. Channel taking more time to start and come to
minimum speed.
This behaviour was not observed during
commissioning.
BHEL stated this may happen due to additional loading of
the fan during starting.
This happens if inlet damper at ID Fan is not closed
properly.
MISC 8. FD Fan trips when MAMSX and ALAMX relays drop
due to momentary voltage dips or voltage jerk
condition.
Suggested to introduce time delay (off delay) of 1.5secs.
for FD Fan tripping when MAMSX drops. Problem solved.
LCI CHANNELS FOR VFD – COMPENDIUM OF FAULTS
Page 27 of 95
MISC 9. Unbalanced field currents when channel is taken
into service.
Due to irregular firing of thyristors in NHVL card.
Replaced NHVL Problem solved.
MISC 10. When 220V DC fails, VFD motor contactor will not
trip even though power to motor is cut-off.
No harm to VFD system due to 220V DC supply failure.
I&C system will issue STOP to both channels. Load side
contactor will trip when 220V DC is re-established. Hence
no modification required.
MISC 11. ID fan tripping was provided through temp.
scanners in addition to direct C&I trippings. Any
malfunctioning of temp. scanner caused ID Fan
tripping.
Temp. scanners replaced. Temp. scanners used for Alarm
purpose only. Bearing and Winding temp. tripping is kept
through C&I only.
MISC 12. Malfunctioning of Door interlock switches provided
in ID Fan panel door (to trip the channel if door is
opened during channel running.) causing channel
tripping.
Door switch bypassed and ensured that door is always in
locked condition during channel running. Interlock switch
will be replaced during next shutdown.
MISC 13. When Ch-1 is running at 400A and Ch-2 is started,
Ch-2 current shot upto 600A for 1 minute and
slowly came down to 400A.
It seems that the flux in Ch-2 was much higher than in Ch-
1. Therefore Ch-2 which is the Slave channel tries to
correct the flux by increasing its armature current and
thus trying to de-magnetise the flux. Flux closed loop in
the slave is also in operation.
NLIB Load fluxes FAB, FBC, FCA in Ch-2 adjusted to the
same values as in Ch-1 by backcharging Ch-2. Tune up
values relating to flux in Ch-2 checked to be the same as
that of Ch-1. Problem solved.
LOAD
COMMUTATION
FAILURE
REV.04
14. Master channel tripping on Load Commutation
failure. Slave channel current remains at minimum
when working with Master, but OK when run
independently.
Channel trips again on Load Commutation failure.
Found in Master channel that the ripple was very high in
28Volts DC when compared to healthy channel. PSFF
replaced. Found Electrolytic capacitor in PSFF faulty in
28V DC circuit. Channel taken into service.
Crowbar test conducted. Found one HPTK card on Load
side faulty. Changed. Master Channel taken into service.
OK. But Slave channel current goes to minimum when
Master is taken into service. Found Analog 0-10V current
LCI CHANNELS FOR VFD – COMPENDIUM OF FAULTS
Page 28 of 95
signal from Master not OK in Slave. Loose connection of
wire at IOMA TB. Rectified. Problem solved.
LOAD
COMMUTATION
FAILURE
R04
14. Master channel tripping on Load Commutation
failure. Slave channel current remains at minimum
when working with Master,but OK when running
independently.
Channel trips again on Load Commutation failure.
Found in Master channel that the ripple was very high in
28Volts DC when compared to healthy channel. PSFF
replaced. Found Electrolytic capacitor in PSFF faulty in
28V DC circuit. Channel taken into service.
Crowbar test conducted. Found one HPTK card on Load
side faulty. Changed. Master Channel taken into service.
OK. But Slave channel current goes to minimum when
Master is taken into service. Found analog 0-10V signal
from Master not OK in Slave. Loose connection of wire at
IOMA TB. Rectified. Problem solved.
FIELD LOSS
R05, 1206, PH
15. Master channel trips on Field loss. ID Fan continues
to run on Slave channel. Due to grid conditions, ID
Fan cannot be taken out of service.
Connections on IOMA TBs removed as per list given in
Annexure-4 for Crowbar test. Incoming wires to
excitation contactor R,Y,B disconnected. Dummy load of
Halogen lamps connected. Conducted exciter test. Found no
current in one phase. Problem traced to bad connection to
one of the thyristor gate in Exciter box in 4 pin white
molex conector Rectified the same.
Conducted exciter test again and found current is
balanced. Normalised all connections and took MASTER
channel into service. Problem solved.
FIELD LOSS
R05, 0407, PH
16. Master Channel trips on Field loss. Due to
constraints, shutdown of fan not given. Exciter test
to be conducted on Master with Slave channel
running.
Connections on MASTER channel IOMA TBs removed as
given in Annexure for conducting Exciter test with other
channel running. Removed cable at output of field exciter
R,Y,B and isolated the same. Connected dummy load at field
exciter output(halogen and incandescent lamps). Performed
field exciter test. Found that one phase current was very
low compared to other. On investigation, found that 4 pin
white Molex connector carrying firing pulses to one
thyristor pin was loose and not mating properly with
connector on NHVL board. Rectified the same. Conducted
LCI CHANNELS FOR VFD – COMPENDIUM OF FAULTS
Page 29 of 95
Field exciter test. Currents balanced. OK. Restored R,Y,B
field of exciter connections and IOMA connections.
Channel taken into service. Problem solved.
NOTE: CARE TO BE TAKEN WHEN DOING THE
ABOVE. CONFIRM THAT R,Y,B POWER CABLES ARE
ISOLATED AND TAPED PROPERLY.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 30 of 95
Category Sl.no. Problem Solution MISC 1. Tripping on undervoltage. 1. Changed C17 on DLIB to 0.47µF from 0.047µF. Did not
solve the problem.
2. LT supply to Control panel changed to Unit LT Bus
instead of Station LT bus.(voltage will not be steady
because external grid disturbances will get reflected
to this).
3. Found that timers in Control Panel were ON delay
instead of OFF delay. Changed timers to OFF delay
type.
4. Problem solved.
MISC 2. One no. thyristor module on load side failed in BFP
10C. All 3 nos. series thyristors got shorted.
Module replaced with healthy power module. Faulty module
sent to BHEL-EDN for repair.
MISC 3. System tripped without any annunciation.
HMPG hanged and test led is glowing.
1. Check if all EPROMs and EEPROMS on HMPG/DMPB
are properly seated. Found OK.
2. Check SEM Lock bar is put and all card top and bottom
locks are firm. Found OK.
3. Check if SEM frame is locked to the panel using the L-
angle provided. Found OK.
4. Found out that even though SEM locking bar is put,
there is clearance between lock bar foam and card.
5. EDN sent lock bars with thicker foam for all SEM
modules so that bars are in contact with all the cards.
Problem solved.
MISC 4. Problem of crowbar test.
Channel current is found hunting for a load beyond
350A.
Malfunctioning of HAIA card.
1. C1-Exciter output found abnormal. One thyristor of
EVC was not conducting. Replaced & OK.
2. C2-NHVL card of EVC found defective. Replaced and
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 31 of 95
No hunting observed.
3. Replace NLIB –Source card.
4. NHVL – only 2 lamps found glowing. Channel manually
tripped. HMPG thoroughly cleaned and restarted. No
hunting observed.
5 . FCLIM values increased. Speed meters for all 4
channels calibrated.
6. Speed regulator gain changed from 35 to 25.
EDN suggested checking of exciter feedbacks during
calibration.
FIELD LOSS 5. Feedback of NHVL card is not coming.
Only 2 Leds on NHVL card are glowing.
Replaced NHVL card.
HMPG, HLCB & NSFE replaced. Cards sent for repair to
BHEL-EDN.
MISC 6. Field current saturates above certain load. ID Fan was getting overloaded. Customer requested to
check whether the loading is as per the load points given in
Motor data sheet in O&M Manual. Also inlet damper
position to be checked. Problem solved.
SOURCE PLL
FAULT
7. Channel tripped on Source PLL Fault. 1. Ribbon cables are tightened.
2. If trips again, recommended to replace HLCB card.
MISC 8. Channel tripping frequently on SEM power supply
(PSFF) failure.
BHEL recommended to decrease AC temperature in VFD
Room for better cooling and provide internal fan for
channel. If not solved, Replace PSFF.
Recommended temperature in AC VFD room is 25°C.
Replaced MCB in PSFF. Problem solved.
MISC 9. Unequal field current in 10A & 10B. 10A taking 20A
more current than 10B.
Load on 10A is more than 10B, at same speed. Hence
higher stator current and also field current.
MISC 10. Motors not attaining full speed of 740rpm for 100%
demand.
Motor does not have sufficient reserve torque to
accelerate beyond a certain speed and excitation current
limit is being reached.
LOAD PLL FAULT 11. PLL Fault and Motor shorted winding Fault. Load side thyristor electrical connections tightened.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 32 of 95
& SHORTED
MOTOR WINDING
Loose connection of Load attenuator wire from Local AC
Busbar found. Problem solved.
FAILURE TO
START
12. Motor rotates in the correct direction very slowly,
when run either from Ch-1 or Ch-2.
Motor was in service earlier from both channels. Individual
channel running was also proved. Therefore suspected
motor.
Found that DC cable in motor from output of exciter
diode bridge to main field had melted at lug point.
BHEL-BHOPAL representatives called to site. Changed
cable. Problem solved.
MISC 13. Output Contactor was not holding after close
command was given. Contactor is M/s.
Telemachanique make Magnetic latch type
CR1BL33M21. Magnet face OK.
Adjusted cam that actuates the contacts for the coil
control circuit on the contactor. Channel taken into
service. OK. Problem solved.
LOAD
COMMUTATION
FAILURE
14. Slave channel of BFP trips on Load Commutation
failure randomly.
SEM grounding, panel grounding checked and found OK.
Changed HLCB card. Problem solved.
SHORTED MOTOR
WINDING
15. Master channel tripping on Shorted Motor Winding. Changed Slave to Master and vice versa. Backcharged
Slave from Master. Adjusted Slave NLIB load fluxes to
same as Master. Problem solved.
LOAD
COMMUTATION
FAILURE
R05, 0107, VI
16. Slave channel of Boiler Feed Pump trips
intermittently on Load Commutation Failure. This is
accompanied by failure of one thyristor device in
Load side bridge.
Checked Earthing of SEM and all other connections
including panel Earth Bus earthing. Found pulse height in
gate test mode on one load side module not OK. Replaced
HPTK card. Suspected track problem in NTDA on one
thyristor during gate test mode. Replaced NTDA.
Added extra wraps to DCOM from NSFC and NSFE pin
37. Replaced NSFE card as this was not passing Selftest.
Pump taken into service with both channels.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 33 of 95
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 34 of 95
Category Sl.no. Problem Solution MISC 1. Flickering of LEDs on HPTK cards both in
rectifier and Inverter in Gate Test Mode.
Problem solved by changing HPTK cards.
BRIDGE
DIFFERENTIAL
PRESSURE
2. “Bridge Differential Pressure” message appearing
in the printer in spite of blowers running.
1. Check cable connection from AFM to IO module. OK.
2. Replaced Air Flow monitor. Problem solved.
LOAD PLL FAULT 3. At rated speed, fluctuations observed in main power
supply to motor, accompanied by unbalanced
excitation parameters.
Voltage sensed by VFD was higher.
Motor speed could not be increased beyond 400rpm
and VFD tripping on “LOAD PLL FAULT”.
1. Jumper setting in HPTK Voltage attenuator circuit
corrected.
2. Exciter phase sequence wrong.
Problem solved.
EDN insisted that VFD room should be maintained dust
free.
FAILURE TO
START
4. Channel tripped on Microprocessor alarm.
Hunting observed. Crowbar and EVC test found OK.
CRSTART modified from 0.3 to 0.5 and started.
Hunting persists.
Snubber bar assembly LTM2 and LTM5 were found open.
Replaced Snubber Bar Assembly & started.
Load current CT feedback cable(10 pin) on SEM header
found reversed. Inserted in correct direction. Problem
solved.
MISC 5. Run light always ON. Backplane wire wrapping problem. Corrected. Problem
solved.
P105
UNDERVOLTAGE
6. Channel tripping due to P105 u/v. Changed DPSA card.
Changed DPSA power supply.
Mounting of power supply found loose(no screw). Also, AC
input to the card has been reduced to 110V by adjusting
tap position to the input transformer. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 35 of 95
MISC 7. Self Test fails at 2001. EDN says problem is in Self test circuits only. Site asked
to go ahead with motor running. This circuit does not have
any function when drive is in service.
MISC 8. Could not go to Gate Test mode. Corrected offset zero on NLIB Load and NLIB Source
FAB, FBC & FCA with test oscillator ON by slightly
adjusting BAL1 and BAL2 potentiometers on NLCB Then
changed MTRFMIN and FLUXS to 0.2 and 0.1 respectively.
Problem solved.
MISC 9. “MAMS relay not getting reset even after VFD is
stopped (Speed is zero).
HRDA card found faulty. Replaced. Problem solved.
MISC 10. Speed suddenly reached 500rpm and unit tripped on
furnace pressure very low.
Due to sudden high set point from I&C 4-20mA signal.
Corrected problem at I&C. Problem solved.
MISC 11. ID Fan Auto control is not working properly. Hunting
in current when Furnace pressure controller is put in
Auto mode.
Customer asked to change P & I values in PI furnace draft
controller in I&C system. Problem solved.
MISC 12. Controller very slow. May damage VFD/motor.
Clearance asked to make controller fast.
Customer asked to time furnace draft PI controller at I&C
system for optimum performance to suit system
requirement. Problem solved.
MISC 13. VFD did not stop with Stop command from DCS,
Filed stop PB. Finally stopped with Emergency Stop
PB from 6.6kV.
Speed does not vary with input signal and
communication to HRDA card fails.
Due to Bushog problem in HMPG Suspected loose
connection between HMPG and mother board on SEM rack.
HMPG cleaned and inserted in rack. Lock bar put. Problem
solved.
MISC 14. Drives reached rated currents at less than rated
speed.
Current drawn at 705 rpm (max.) is exceeding
rated current in 3 motors.
Current limit to be raised by raising the value of SRCLSC
by 10% to increase the speed further. This can be done as
there is margin in motor and VFD. Problem solved.
MISC 15. HMPG IMOK Led was going OFF resulting in tripping
of 6.6kV breaker.
Problem temporarily removed after tightening of
SEM front bar plates. Problem persists & repeats
after 2 days.
Due to vibration of SEM Rack.
Source of vibration-SEM Rack cooling fan. Fan replaced.
Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 36 of 95
MISC 16. During starting, Stop command was being given by
C&I system.
Due to higher time taken to achieve minimum speed of
145rpm from standstill. Timing in C&I increased from 30
secs to 60 secs. Problem solved.
MISC 17. One no. Neon lamp of XPTN card on load side
thyristor module is not glowing.
Corresponding thyristor found failed. Replaced thyristor
module and sent faulty thyristor module to BHEL-EDN for
repair.
MISC 18. Current and voltage at motor isolator switch is not
matching with the corresponding values at control
and excitation panel.
There will be difference in indication upto 25Hz. Over this
the indications will be nearly same. This is due to
saturation in the metering core of CT at low frequency.
Indications in VFD panel to be taken as actual.
MISC 19. The maximum speed at 100% demand from control
room is below rated speed. i.e. 725rpm in all 3
motors.
Current drawn at 705rpm is exceeding the rated
current of all 3 motors.
Since VFD is a current limited drive, speed can increase
only upto the current limit set. Customer asked to check
inlet damper position and verify whether it is as per
recommendation.
MISC 20. Microprocessor alarm appears. IMOK of HMPG and
NLCB disappears and subsequent tripping of 6.6kV
breaker occurs.
Frequent tripping of Fan on various faults.
1. Observe whether the fault appears under the conditions:
a. Only Auxiliaries ON, HT supply OFF to VFD
b. With HT & auxiliaries ON, drive not running
c. With drive running.
2. Check voltage levels of P5, P15, N15 & P28 supplies.
3. Check the status of Alarm Word.
4. Replace all 6 EPROMS (4 on HMPG & 2 on DMPB).
5. Check if SEM earthing is as per SEM Earthing
document.
6. Since sl.1 to 5 did not lead to any definite reason,
SEM rack was changed. The original cards were
returned. Lock bar of SEM put.
7. Problem was solved.
MISC 21. Fan tripped with Motor Overtemperature Alarm and
Overtemperature Trip. Found MCBs CB1, CB2, CB4
and CB13 in control panel tripped without actual
1. Could have been only due to fault in the circuit
connected to CB1 breaker. Checked all auxiliary
circuits including 110V contactors connected to CB1
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 37 of 95
temp. rise in motor.
Subsequently motor did not start and “Rotor
position start alarm” was observed.
breaker for healthiness.
2. Motor opened and inspected. Found exciter wiring had
soot covering at some spots.
Exciter stator winding round carbonised. Motor
needs to be repaired/replaced with new one. Motor
sent to Bhopal for rectification of exciter rotor.
Received back at site.
LOAD
COMMUTATION
FAILURE
22. Channel tripping intermittently on Load Commutation
failure.
Channel tripped again after few hours.
Self test conducted. Speed feedback circuit found
malfunctioning in NLCB/DLCB.
Crowbar test conducted. Current feedbacks O/C
protection circuits checked, adjusted and started.
Channel tripped on “Load Commutation failure” again
after few hours.
HMPG, 5 nos. of NTDA cards changed.
Load side bridge thyristors, snubber ckt., CT circuit,
gating circuits checked. All terminations on HPTK and
NTDA cards checked for loose connections and
soldered/tightened/replaced wherever required.
DLCB replaced.
Firing pulses and load side HPTK cards, NSFC, related
cables checked. 2 HPTK cards on load side, reference for
detection of UV of gating supply was 1.3VDC while in
others it was 1.8VDC. This reference adjusted to 1.8V in all
HPTK cards.
Gating power supply voltage was low. Corrected this to
required level. Self test and Gate test passed. Channel
taken into service.
MISC 23. HMPG and NLCB IMOK going OFF. SEM cards to be thoroughly cleaned by blowing over SEM
with blower.
Check SEM lock bar is installed correctly and firmly. SEM
module is anchored properly. Drive taken into service.
GATING SUPPLY 24. UV chattering of relay in PS7 power supply. NTRF card in PS7 changed. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 38 of 95
UNDERVOLTAGE
FAULT
Card sent for repair to BHEL-EDN.
MISC 25. Drive tripping on Microprocessor Alarm and Stack
fault.
This type of problem is due to spurious interrupts which is
normally attributable to grounding.
Found that earth bus at rear of panel was sheared off at
panel end and also earthing bus was not continuous.
Incorporated jumper cables on earth bus and tightened
connections. Incorporated extra connections between
2A/34, 2B/34, 2C/34 to DCOM. Drive taken into service.
MISC 26. Channel LM100 Breaker from 110V UPS tripping
because current taken is too high (14 Amps). When
only SEM and IOMA are ON (drive stopped), the
current is 4 Amps. When drive is started, then
current jumps to 14 Amps. Normally, it should be
about 11 Amps.
PS70 output voltage was 84Volts DC on load. Voltage
lowered to 80 Volts DC by adjustment of pot. on NTRF.
Current came down to 11 Amps. Breaker did not trip.
Problem solved.
MISC
REV.04
27. Source breaker trips on Microprocessor Alarm
through SWGR relay on IOMA even when drive not
running.
Found that P28 fuse on PSFF was not properly put in
holder. Same tightened. NLIB Source changed and offset
adjusted to zero on FABR, FBCR, FCAR with Source
breaker closed. Drive taken into service. Problem solved.
SOURCE
UNDERVOLTAGE
R05, 1206, PH
28. ID FAN is 6 pulse drive. Drive starts and goes to
minimum speed but does not increase beyond this
either in LOCAL or REMOTE reference. Source
Undervoltage alarm comes frequently and MAMS
relay chatters. Motor currents unbalanced.
NLIB and NSFC load cards changed. Problem persisted.
Found that wire had got cut in the lug and was giving loose
connection at IOMA TB input LBKRS. The same was re-
lugged and tightened. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 39 of 95
Category Sl.no. Problem Solution MISC 1. Unbalance motor Currents upto 1.5A in blowers. Vendor has informed that unbalanced current of the motor
cannot cause any damage or reduce overall life expectancy
of blowers.
MISC 2. Failure of cards and intermittent failure of VFDs. Failure rate of cards could be high during commissioning
but extremely low after stabilisation.
Analysis-Most of the component failures attributed to
voltage mix-up and wrong cabling during pre-commissioning,
handling, dust accumulation during commissioning.
LOSS OF
COLLING FAN
3. Channels tripped on Blower loss. Due to tripping of blower supply to ID Fan because of
flashover in ESP LT switchgear.
Customer requested to provide individual channel’s blower
AC supply from 2 separate sources.
Customer was advised that the same is not required, as
such problem has not occurred at any other site. Reason
for flashover in ESP switchgears to be analysed and
corrective action to be taken.
MISC 4. PSFF power supply MCB trips frequently even
though load is normal.
Replaced MCB of PSFF. Problem solved.
MMI FOR VFD 5. 1 no. Line driver found defective.
On executing VFD MMI S/w, after 2 minutes,
program came out of main exe. File. “Drive status
had also not got updated.”
1. Replaced. Defective line driver sent for repair to
BHEL-EDN.
2. Check if Serial intelligent card & Reed relay card are
available.
3. Check 24V DC Jyothi Relay in C&EXE panel is getting
energised on program execution. If OK, Connect 25 pin
connector to door mounted printer. Check that
messages are printed on printer.
4. Check MMI system connections as per scheme.
If all connections/hardware are OK, Pink window –
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 40 of 95
Drive Status should appear on MMI screen, else Blue
window – Link Failure appears on MMI screen.
MISC 6. Com Port of one Laptop supplied for VFD is not
working.
1 computer of VFD-MMI not working.
Repaired by BHEL-site through laptop vendor.
Mother board replaced by computer vendor at site.
LOAD
COMMUTATION
FAILURE & LOAD
PLL FAULT
7. Channel tripping on Load Commutation Failure.
Channel tripping intermittently on faults “Load PLL
Fault Load Commutation Failure, Motor Winding
Shorted & Power Supply PSFF failure.”
SEM earthing found not proper. Same rectified.
3 nos. HPTK modules and 1 no. PSFF changed.
MISC 8. 3 MOVs of 440V 1A,2A & 3A found burnt during
inspection and maintenance work. Found incorrect
connections,
Fuses feeding MOVs – No failure observed. Found MOVs
burnt. Found wrong connection in panel.
Advised to change all 9 MOVs 1A to 1C, 2A to 2C, 3A to 3C.
MOVs changed. Problem solved.
LOAD
COMMUTATION
FAILURE
9. Slave Channel tripping on Load Commutation failure. Channel back-charged with Source breaker open and Load
breaker closed. FAB, FBC, FCA in NLIB load found with
large DC offset.
Changed NLIB card and adjusted DC offsets to less than
30mV and balanced AC voltages of FAB, FBC, FCA. Channel
taken into service. OK. Problem solved.
MISC 10. Both Master and Slave channel of one ID Fan
tripped out. In Master channel, Source and Load
breaker tripped. In Slave channel, only Load breaker
tripped.
Flashover in Source side of Master channel. Master
channel isolated and Slave channel taken into service.
Found source side AC and DC filter fuses blown and also
cable tapping from busbar to filter fuses burnt. MOVs on
Source side OK. Fuses and wires replaced. All clearances
are more than adequate. Cause of flashover not known.
Channel taken into service. OK.
MISC 11. Fan-B Ch-2 tripped. Following were noticed: 1.
Source breaker tripped. 2. FT1 indication observed
at VFD end. 3. HMPG IMOK LED was not glowing.
Crowbar test done – Found O.K.
Gate Test done - Found O.K.
Self Test done – Found O.K.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 41 of 95
4. There was huge current hunting only in this
channel before tripping.
Primary injection tests in all 4 CTs done. Found O.K.
Finally problem was traced to improper earthing in
electronic earth pit. Salt added. Drive started and found
O.K.
GATING SUPPLY
UNDERVOLTAGE
R05, 0207, PH
12. Channel trips on Gating Supply Undervoltage. Output voltage of 70Volts Power supply measured under
Gate test mode. Showed OK 82 Volts DC. Checked voltage
of Power supply healthy signal from each of the HPTK
cards going to XTFH diode circuits. All 12 voltages OK.
Changed XTFH card and Channel taken into service.
MISC
R05, 0407, PH
13. Channel tripped on Fault. Found that all LEDs on
HRDD are ON. FT1, FT2 and RST LEDs on NLCB
ON. 6 Amps 28V fuse on PSFF adjacent to circuit
breaker blown.
From the problem it was inferred that the problem could
be in IOMA module. Isolated by removing 28 Volts Power
supply from PSFF connector feeding IOMA. Replaced
PSFF 6Amps fuse. Swithched ON PSFF. 28Volts fuse did
not blow. But all LEDs were glowing as before.
Switched OFF PSFF power supply. Removed all 4 cards in
IOMA module. Put back IOMA power supply connector on
PSFF. Switched ON PSFF. 28Volts fuse on PSFF did not
blow. Inserted one card after another in IOMA switching
OFF PSFF everytime. Found that 28Volts 6Amps fuse
blew when HRIA/2A card was inserted. Changed HRIA
card. Problem solved. Channel taken into service. OK.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 42 of 95
Category Sl.no. Problem Solution MISC 1. Incoming MCCB to IOMA PSFF tripping due to
inrush currents.
Breaker setting adjusted according to site conditions.
Problem Solved.
MISC 2. Channel did not start smoothly. Found load C.T polarity reversed after examination of Load
current waveform w.r.t. load firing pulses. Corrected
polarity. Problem solved.
MISC 3. Hunting observed in current & speed. Parameter SRGAIN tuned.
Problem solved.
MISC 4. During exciter test on channel, resistors R70, R71
replaced from 56 Ohms to 46 Ohms to adjust
burden of CT
Feedback as required adjusted with potentiometer on
NHVL.
Problem solved.
MISC 5. Self test not passing because offset value was not
within the range.
DC offset on source & load NLIB FAB,FBC and FCA could
not be adjusted within 30mV with test oscillator ON by
adjusting BAL1, BAL2 pot’s on NLCB. NLCB replaced.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 43 of 95
Problem solved.
MISC 6. HMPG IMOK not coming. Replaced HMPG with EPROM sets of tested card (6
EPROMS). Card sent for repair.
MISC 7. Pulses not getting distributed to thyristor stack
individually in gate test mode.
Card XTFX in source side found defective. Replaced.
Problem solved.
MISC 8. ID Fan ‘ON’ check back derived from its speed
being above a certain value
(MAMS). During starting MAMS chatters as speed
hunts slightly resulting in ID Fan ON/OFF toggle.
This gives auto start to shutdown sequence.
Automatic initiation of shutdown sequence due to ID fan
‘OFF’ status will be delayed. Introduced time delay OFF
logic for MAMS input at I&C. Problem solved.
MISC 9. VFD demand goes to max. when both ID Fans are
OFF. This prevents reducing the VFD demand to
min, when taking the first ID Fan into service.
This command is removed in I&C system as it is not
necessary.
Problem solved.
MISC 10. ID Fan VFD given a protection trip from Source
Breaker OFF condition but also source breaker is
given trip on VFD OFF condition, thus creating a
logical problem.
Source breaker trip due to VFD OFF condition will be
removed and instead will be given a trip command on its
‘Electrical protection acted’ input being true. This is
implemented at I & C. Problem solved.
LOAD
COMMUTATION
FAILURE
11. Channel tripping on Load Commutation failure LMARG was changed from 25° to 30°.
Found P28 was 21.5Volts. Site asked to change this to
minimum 24V level during gate test mode. Problem solved.
Changed back to 25° after channel was normalized.
MISC 12. Any electrical supply system jerk causes drive to
trip.
Presently UPS feeding VFD is not fully commissioned and
UPS is running on By-pass. Problem will not occur if UPS is
commissioned.
MISC 13. Customer expressed that ‘Auto fault Reset’ facility
is not available.
EDN informed that facility will not be given. It is
required that the maintenance engineer has to come to the
VFD panel to find out the fault and take corrective action
before re-setting.
MISC 14. Coil for OEN make relay found burnt in IOMA Suspected quality problem. Relay changed. OK.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 44 of 95
Reason unknown.
MISC 15. NLCB gives IMOK indication but fails
during self test of NCLB card.
DLCB card components R1 & C1 not matching as per
scheme. Changed from other card. Problem solved.
MISC 16. NLIB gives IMOK indication but fails in Self Test. Daughter board components R22, R31, R40, R23, R32, R41,
R60, R68, R72 not matching as per scheme.
Changed the components as required and also adjusted the
gains of FAB, FBC, FCA as per commissioning procedure.
Problem solved.
SOURCE
COMMUTATION
FAILURE &
SOURCE
OVERCURRENT
17. Drive tripped on “Source Commutation Failure”.
Drive restarted and motor tripped without picking
speed on “Source Backup Overcurrent Operated”
tripping Source breaker also.
Gate test and Crowbar tests passed.
Advised to conduct EVC test and crow bar test. Also
inspection of output contactor contacts advised.
Found that one of the thyristor cells in the load side
bridge had got shorted. Replaced thyristor module & sent
the faulty module for repair to BHEL-EDN.
Problem solved.
I/O PROBLEM 18. Both channels commissioned but not able to take
both into service simultaneously because of a
missing feedback due to HROA card.
Current hunting after that.
HROA card replaced. Simultaneous operation possible.
Problem solved.
HROA card sent for repair to BHEL-EDN.
MISC 19. Current sharing problem between channels. Actual currents were balanced. Meter on LCI channel not
showing correctly. Meter adjusted OK with pot. IM on
NLIB.
FAILURE TO
START
20. VFD failed to start and Rotor failed to start (Bit 1
of ALARM WORD) displayed on printer.
Problem in DC field and exciter on synchronous motor.
Motor changed in presence of BHEL-Bhopal person and it
is running OK.
MISC 21. Laptop battery back up not working. Customer has asked to send 2 battery back ups.
EDN says that Laptop PC can be fed from UPS supply
available in VFD panel. As such battery back up is not
required in laptop PC for VFD maintenance.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 45 of 95
MISC 22. Unit tripped on received AUTO OFF commands.
WSPOSE relevant alarm display was “Auxiliary
Supply failure”
Customer requires that 24V DC and 220V DC
supply failure be separated.
Site : Logic built in VFD such that a time-delayed timer 0-
35secs. (set to 3secs.) drops when either of 24V or
220V DC supply fails. Contacts of this timer used for
Source drive breaker Start Perm. and its inverted status
used for generating AUTO OFF commands to source
breaker cards simultaneously.
EDN does not recommend separate logics for 24V & 220V
DC monitoring, as both 24V DC and 220V DC failures
should trip the drive.
MISC 23. High vibration noticed in fans at speed above
650rpm (Speed at unit F.L.condition is <600rpm)
Resonance is being observed from foundation at
speed>650rpm. However, vibration is in good zone.
BHEL-Ranipet recommends that status of spring
compression can be checked during annual maintenance
shut down.
MISC 24. VFD trips when small system jerks occur. Time delay of 2 secs. already incorporated to tide over
the problem. Customer has been asked to look into the
source of the swing/jerk and take appropriate action.
LOAD
COMMUTATION
FAILURE
25. When Ch-2 is started with Ch-1 running normally,
Load sharing is equal, but Ch-2 tripped after 5-10
hrs
28Volts DC of SEM power supply checked and found to be
atleast 24V. Also its waveform did not have any ripple.
LMARG increased by one degree. Problem solved.
MISC
REV.04
26. Heavy hunting in Slave channel when paralleled with
Master. Also Master current hunting when running
alone, but oscillations are not of large magnitude as
in Slave. Slave runs OK when run alone.
Shutdown of Master channel taken and isolated it from
Slave by removing connections on IOMA TBs for Rotor
Position/other channel running and Torque reference input
and Torque reference output.
Crowbar test conducted on Master with Slave in service.
Found LTM2 on Slave defective. Replaced card. Master
taken into service. Found OK. But heavy hunting in Slave
continued. Found that wires were loose on IOMA TB 12
pulse Input signal 2BF IOMA TB7/16,17. Wires on TB
tightened. Slave taken into service. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 46 of 95
Category Sl.no. Problem Solution MISC
1. When individually run, both channels run OK. When
both channels put on parallel for equal sharing of
current, it could not work. Current in Ch-2 became
0.
Ch-1 Tripped due to MP module power supply failure.
Ch-2 tripped due to Stack failure.
Only once, channels could run in parallel operation,
but local stop PB did not respond, tripping could be
done by operating local/remote selector switch.
Problem seems to be due to 240V supply fed to electronics
or malfunctioning of circuit breaker in PSFF module. EDN
has asked site to carry our the following & give feedback.:
a. Put both channels in Gate Test mode at the same time
by changing MTRFMIN to 0.2 and FLUXS to 0.1 &
putting NLCB switch up. DO NOT SAVE. It may take
about 5 minutes for pulses to be released.
b. Check input supply at sheet 1BB of scheme. Change tap
of trf. to get 110V on sec. of T1.
Check 28, +5, +15, -15 volts on SEM rack OK.
Check 70V DC from gating power supply OK. Should be
atleast 75V DC during gate test.
c. Quit gate test by putting NLCB switch down and
resetting MP.
d. Check 220V DC supply to VCBs OK.
e. Run up Ch-1(master) to minimum speed. Check
LMODE=3.
f. Run Ch-2(slave). Check LMODE goes to 3 in slave. If it
does not, slightly lower MTRFMIN and FLUXS in Ch-2.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 47 of 95
g. Power supply tripping problem in Ch-1 sorted out.
MISC 2. Following problems during parallel running of 2
channels:
a. Individual load breakers do not trip with remote
trip command/local stop PB. Only Run relay
drops & MP does not issue a trip command via
RUN relay.
However process trip commands trip load side
breakers at a time for both channels as
expected.
b. During loading, fan speed rises upto 35% speed
ref. Command. And beyond that speed does not
rise. Stator current hunts from min. to max.,
but speed does not rise.
a. Monitor 105V DC level on IOMA TB3-9,10 when RUN1
& RUN2 relays in control panel drop. Check operation
of load breakers, independently by removing plug-in
type RUN relay in IOMA and simulate Load Breaker
operation. Source breakers must be OFF when doing
this test.
Mistake in wiring chart of Ch-2. This was the cause of
Ch-2 not switching OFF when STOP command given
from C&I. Problem solved.
b. Observe INVLIM during normal running and when
hunting happens by continuous display of INVLIM.
The value of INVLIM displayed will tell the type of
fault. Please do the following:
1. Increase LMARG to 0.3 from present 0.16. Run
drive and see if hunting persists. Hunting
persisted.
2. If it persists, Change LMARG back to 0.16. Change
resistor R60,R68, R76 in NLIB to 100K from 180K.
Run & see if hunting persists, Changed resistors.
Hunting persisted.
3. If it persists, change above resistors from 100K to
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 48 of 95
56K. While changing resistors, NLIB to DLIB
Ribbon cable connection is to be removed.
Hunting remains.
Inadequate excitation caused dip in Armature voltage
leading to hunting of speed and armature current.
ALPHFLD was reaching 255. Exciter current was
reaching 63A LRMS-too high for the load. Reversed
exciter stator cable thereby changing the phase
sequence. Problem solved.
MISC 3. Motor current calibration on VFD C&EXE panel. Run both channels at min. speed. Check LMODE=3 in both
channels. Measure trf. sec. winding current with clip-on
meter. Since trf. current = motor current, adjust
NLIB/DLIB pot. IM so that panel meter reads correctly.
Note that at minimum speed current will be minimum &
steady.
MISC 4. Running VFD when ID Fan handles air instead of flue
gas. Speed does not go to Maximum.
Since density of air is much higher than flue gas, it will not
be possible to run the drive to 540rpm as current will
reach the limit values before this speed.
LOAD
COMMUTATION
FAILURE
5. Channel tripped giving Commutation failure.
Both channels tripped due to fan vibration very
high-process trip.
1. Changed XL compensation resistors in NLIB load R60,
R68, R76 from 180K to 67K. Tripping continues.
Resistors changed back to original value.
2. P70 Volts output changed to 80 Volts during gate test
mode. Problem solved.
3. Vibration problem attended by mechanical
maintenance group.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 49 of 95
MISC 6. Channel does not start. On excitation board, only 2
LEDs glowing on Start command.
Power supply unit failed.
Printer not receiving data from the MP.
1. NHVL excitation board failed in Field Exciter.
Replaced. OK. Failed board sent for repair.
2. PSFF module replaced. OK. Failed PSFF sent for repair.
3. Printer replaced.
I/O PROBLEM 7. Motor decoupled smooth in both channels. While
starting the fan on Ch-1, ammeter reading does not
go beyond 400A whereas in running it goes upto
600A and comes back for any speed increase
command.
When fan started through ch1, fan did not start,
rotor oscillating and stator current hunting. Ch-1
stopped and ch-2 started. Ch-1 paralleled. Found
OK. Ch-1 OK even ch-2 stopped. Ch-1 started
independently before rotor came to rest. Ch-1 does
not start from rest position.
11 nos. Modules found defective. Replaced.
Ch-1-Polarity of CT inside excitation board was changed as
IFB waveform not found OK. During power-up, before
restarting, MAMX in picked-up condition though HROA-R2
LED not glowing. Load breaker closed without any
command. Self test failed in 230D. HRDD, NLCB
suspected defective, Replaced & power On. MAMX picking
up. HROA in 1B failed. Spark observed in K3 relay body.
FU-6 blown in HROA. In MAMX, suppressor block (R-C
net) changed as lugging was not OK. IOMA changed. HROA
connector found burnt. HRDD found defective.
All replaced. Self test passed. Fan started.
4-20mA for remote indication was not there. NLCB
changed. OSP and SPM setting was done. Fan run and
paralleled.
Ch-1 fault and not starting. All LEDs on HRDD glowing.
HRDD replaced. Remote speed indication and local speed
indication became zero. NLCB changed and ID fan started.
Problem repeated again.
Problem maybe in exciter module or NSFF card. Check
waveform during field exciter test at TP IFBK in NSFE.
Compared with healthy channel. Also, checked exciter
pulses SIG1 to SIG6 at NSFE.
One of the thyristor pulses was missing, Pulse trf. on
NHVL exciter board failed.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 50 of 95
When motor started through VFD Ch-2, did not start and
tripped on Source & load OverCurrent & ground faults.
During meggering on motor insulation , IR value found very
low. Problem related to Motor insulation, BHEL-Bhopal
contacted. Motor end covers opened & 1 conductor was
observed to have turned black. This was due to insulation
failure which resulted in high earth fault. Motor
replaced. Same problems observed. Also spurious
trippings/startings observed in Ch-1.
IOMA modules replaced in Ch-1 & 2. PSFF replaced in Ch-2.
Fan Run OK.
MISC
LOAD
COMMUTATION
FAILURE &
SOURCE
COMMUTATION
FAILURE
8. Ch-2 self test not passing. DC Offset not getting
adjusted to zero volts.
During trial run, Ch-1 “Commutation failure fault
appeared.
Additional earthing provided. NLIB card replaced. Offset
voltage made zero in NLIB Source & NLIB Load FAB, FBC,
FCA by adjusting BAL1, BAL2 pot’s in NLCB. Self test
passed OK.
NTDA card on thyristor modules resoldered wherever it
was suspected dry solder present. Fans run OK.
I/O PROBLEM 9. Failure of IOMA modules. Seems to be a chance of voltage mix-up in P105 and IOMA
output contactor circuit. Mix-up could be from inside the
panel or from outside IOMA.
Found that there was no voltage mix-up in panel side.
IOMA modules suspected.
Sent to BHEL-EDN for repair. Found problem of open PCB
tracks on IOMA module backplane and also tracking
between PCB tracks. Backplane PCB’s on I/O module
changed. Vender de-listed. Quality problem. Problem
solved.
FAILURE TO
START
10. Ch-1 of ID fan-starting and running
OK.
Found in Ch-2 that the load side CT polarity is reversed
after observing the waveforms of load side firing pulses
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 51 of 95
Ch-2 (slave) of ID fan- Does not start. But runs OK
after paralleling with Ch-1.
Tune-up parameters are same in Ch-1 & Ch-2.
w.r.t. Load side CTs. Corrected CT polarity.
Problem solved.
LOAD PLL FAULT 11. On starting, Load breaker trips. Load PLL Fault or
Load Overcurrent or Shorted Motor Winding
message appears. SUPP Led not glowing.
Found that NSFC load card was loose and not properly
inserted in rack.
Inserted card in rack and put SEM lock bar. Drive started
and found OK.
GROUND FAULT 12. Ch-2 tripping on ground fault intermittently and
thereafter as soon as channel was paralleled to Ch-
1.
Action taken:
Checked tightness of all power connections including earth
bus. Found OK.
Checked SEM earthing. Found OK.
Checked gate pulses and any loose connections etc. Found
OK. Backcharged Ch-2 and checked load fluxes on NLIB
load. Found OK.
Crowbar was conducted with all doors and backcovers
open with CRSTART=0.
Found sparking on one of the load side capacitors in Fan &
filter panel. It was seen that the discharge resistor
connected across capacitor terminals was very close to
capacitor body leading to the sparking and hence ground
fault.
Corrected position of resistor and its leads for adequate
clearance from capacitor body.
Problem solved.
I/O PROBLEM
REV.04
13. Channel tripping on I/O address problem. HMPG
Bushog LED comes ON.
HLCB and HAIA cards changed. Problem persisted and
Bushog LED on HMPG coming ON after 2 minutes. HMPG
card changed retaining old DMPB. Channel taken into
service. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 52 of 95
LOAD PLL FAULT
R05, 1007, PH
14. Master channel trips on Load PLL Fault. Backcharged from Slave channel. Found that NLIB load
FBC AC voltage was oscillating. Changed NLIB Load card
and set the values of FAB,FBC,FCA as in Schematic drg.
Sht. 1DA. Channel taken into service. OK. It is inferred
that OPAMPS in NLIB load may have drifting problem in
FBC circuit. Sent card to BHEL-EDN for repair.
Formatted Table
LCI CHANNELS FOR VFD – COMPENDIUM OF FAULTS
Page 53 of 95
Category Sl.no. Problem Solution MISC 1. Door mounted printer not
printing messages.
Found one wire wrap wire carrying printer signal was cut on
SEM. Re-wrapped wire. Problem solved.
FAILURE TO
START
2. Drive not picking up speed. Runs at a speed below
minimum speed continuously.
One load side thyristor module not firing properly.
Problem traced to loose connection on wire lug carrying
firing pulses. Re-crimped wire. Problem solved.
FIELD
OVERCURRENT
3. Drive trips on Field Overcurrent or Field loss
during start.
415V auxiliary supply for VFD was fed from DG set. The
main 11KV supply was fed from Electricity board feeder.
Since the Source Thyristor bridge and Excitation
Thyristor bridge work on the some PLL (Phase Locked
Loop), both bridges must be fed with electrical power
derived from the same power source.
Changed auxiliary power 415V source feeder. Problem
solved.
FAILURE TO
START
4. Motor not starting in uncoupled
condition.
Found that parameters in software were parameters for
coupled condition. Changed to uncoupled condition
parameters. Motor Run. OK.
MISC 5. Motor starts and heavy vibration observed in Motor
and fan.
Found that no firing pulses to STM3. Also source 11kV
current unbalanced.
Changed HPTK card on STM3. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 54 of 95
Category Sl.no. Problem Solution MISC 1. Channel tripped. Found that DMPB IMOK was not
‘ON’. LVSH from PSFF power supply was giving ‘high’.
Also HMPG was not communicating properly with
Laptop PC.
See DMPB IMOKP15, N15 at PSFF. IMOK LED of DMPB lit
up. Channel taken into service. OK. Problem solved.
MISC 2. Frequent tripping of VFD transformers on process
trippings.
EDN did not recommend introduction of any extra
breaker/contactor/switch giving the following explanation:
1. LCI decides to open the Load or Source breaker or
both depending on the type of fault.
2. Emergency stop conditions are rare as this represents
emergency conditions.
3. Once unit starts generating, the no. of operations of
the source breaker becomes extremely low.
4. Similar interlocks for source breaker existing in
earlier drives already supplied and in service. No
transformer failures encountered to date.
MMI FOR VFD 3. VFD MMI:
1. While carrying additional tests for Line drivers
mounted in C&EXE panel, R+ and T+ led are glowing
but key pressed in not getting printed on VT100
screen.
2. Link fail is coming in window during Integrated
test for MMI system.
Check all cabling is as per document.
1. Check that cable connection that has been made
between the VT100 terminal and the line drivers is a
one-to-one connection, i.e. Connect the wires to the
respective as follows: 2-2, 3-3, 7-7 (and connect 7
to ground) , check that individual line drivers are OK
and then conduct Loop-Back test.
2. Check if the software is reading the MPCC card and
the Reed-relay card. For this, take out the above
cards from their respective slots inside the PC. Run
the MMI.exe file. The following should happen:
a. A message will be printed out: MPCC/Reed-relay
card not in place.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 55 of 95
3. Error no. 13 is also appearing in editor mode.
4. In O&M panel, while switching on ‘PON’ and ‘TL’
both LEDs glow, whereas in C&EXE panel, ‘R+’
and ‘PON’ LEDs glow and when wire is looped by
shorting T+ to R+ and T- to R- then ‘TL’ LED
glows.
b. The MMI window will not appear.
If the message dos not appear and MMI window
appears-contact BHEL-EDN.
If the above is OK, put back the 2 cards and re-
execute the MMI.exe file and then perform the
Integrated test. While conducting the test, start
with conducting it only on a single C&EXE panel i.e.
switch off all the other line-drivers in the O&M panel
and the other C&EXE panels. Switch on only the line-
driver in one C&EXE panel and the line driver
corresponding to this channel in the O&M panel. It is
very important that the other line-drivers be
switched off since the open connection at the D-
connectors can give rise to link failure.
3. After the above tests have passed, check whether
this error message still appears.
4. Do this test first on the O&M panel Line-driver:
While switching on this line driver, switch off &
remove the connection between the C&EXE panel line
driver & the O&M panel. i.e. do this check with this
line driver totally isolated. Remove the shorting
between T+ & R+,T- & R- if present. The TL Led
should not glow. Then short T+ & R+,T- & R-. Now the
TL Led should glow.
Perform the same test on C&EXE panel line driver and
check that the same is OK. Of problem persists, swap
the line drivers and check. If the above is not
happening, the individual Line Driver buffer may have
got spoilt and the same needs to be replaced.
RS232 interface adaptor found defective. Replaced.
Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 56 of 95
MISC 4. Current hunting problem during loading of drive
motor accompanied by voltage collapse.
Phase sequence at motor exciter terminal box changed.
Problem solved.
MISC 5. Loading of RPM meter and current meter. BHEL-EDN suggested to put a resistance of 200 Ohms
across the respective IOMA TBs after disconnecting
external cables. EDN to revert back after receiving the
reading on the door module meters and the mA current
through the 200 Ohms resistance.
Problem traced to higher loading in C&I. Problem at C&I
sorted out. OK.
LOAD
COMMUTATION
FAILURE
6. Ch-2 tripped on “Load Commutation Failure”. NSFC Load card found defective. Replaced. Problem
solved.
GATING SUPPLY
DIP
7. 1. Ch-2 tripping on “Gating Supply dip”.
2. After 12 hours running, irregular firing and no
LED indication on leg STM3 reported by
customer. Machine did not start after stopping.
3. During starting current going to 580A then
coming to zero and then going to 500Amps, then
stabilizes around 100-150 Amps.
1. HPTK card of STM3 found defective. Card replaced.
OK.
2. One HPTK card of STM3 & one NSFC card found
defective. Replaced and Machine started.
BRIDGE
DIFFERENTIAL
PRESSURE
8. Channel Tripping on Bridge Differential Pressure. Lowered the differential pressure setting in Air Flow
monitor. Problem solved.
SOURCE
COMMUTATION
FAILURE
9. Channel tripped on “Source Commutation failure”
when running on no-load.
One no. SCR in STM2, all three SCRs in LTM1 and 2 SCRs
in LTM3 showing zero resistance. Problem cause is the
loose connection of T2 control trf. in LCI panel.
Connection tightened. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 57 of 95
MISC 10. Current hunting problem in channels. One no. thyristor leg found defective. Replaced and
problem solved.
LOAD
COMMUTATION
FAILURE
11. Channel tripped on “Load Commutation Failure”. Following tests were carried out:
1. Resistance across all the thyristors checked. Found
satisfactory.
2. Fuses in all HPTK cards checked. Found OK.
3. Self test failed in 2901 during testing of HRDA(1A),
HISA(1B) & I/O module.
Replaced HRIA (I/O 2A), HROA (I/O 2B), HISA (1B).
Fuse & 105V supply checked. Continuity of ribbon cables
from I/O module to SEM checked.
Problem persists.
Dust ingress on SEM Electronic rack cards & HPTK
thyristor pulse trf. card found to be the problem. Dust
removed by air blowing.
Problem solved. Channel taken into service.
GATING SUPPLY
DIP
12. Problem of Gating supply dip & LED not glowing in
STM3 NTDA card.
One thyristor of STM3 found short. Replaced. Gating
supply UV problem persists.
MISC 13. Failure of as many as six thyristor legs in one unit
and 2 thyristors in another unit.
Customer asked for an expert thorough analysis at site.
Dust level on the cards in the electronic rack & in the
thyristor power modules found high. This found to be the
possible cause of failure after thyristor failure analysis
done at BHEL-EDN.
LOAD
COMMUTATION
FAILURE,
SOURCE
OVERCURRENT &
FIELD LOSS
14. 1. “Load commutation failure” leading to tripping
of the fan.
2. “Source Overcurrent” fault
leading to tripping of the fan.
3. “Field loss” fault on start-up and unable to start
the fan.
Excitation circuit thoroughly checked up. Found
terminations in ‘C’ phase and the current feedback CTs
were loose. Terminations tightened and ‘EVC Power test’
conducted.
Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 58 of 95
MISC 15. 2x500MW plant not able to generate more than
480MW when only 3 channels of ID Fan are
available.
Damper position increased to 85% as per BHEL-Trichy
recommendation. Problem solved.
MISC 16. Motor currents in 2 channels of ID FAN A suddenly
shot-up from 476.95A/466.8A to
741.02A/749.22A, whereas speed varied from
462.89/488.89 to 470.95/504.64 rpm. Sudden
increase in speed and current lasted only for a few
seconds and the values came back to their original
level.
BHEL-EDN rep. Has explained to customer that this
problem is related to reference from I&C. Not a VFD
problem.
MISC 17. Ch-2 not taking over when ch-1 tripped due to any
fault. Ch-2 not starting individually.
Problem traced to failure of fuse in HROA-1B card. Same
replaced.
Ch-2 started individually and in dual mode and operation
found normal.
Changeover and taking over of either channel in case the
other trips has also been found in order.
MMI FOR VFD 18. MMI of ch-2 not working. Circuits of door mounted printer port of VFD, line drivers
(VFD), line drivers (O&M), Multiplexer, Demultiplexer,
Junction base, MPCC card checked and found in order.
Data transfer and communication from SEM suspected.
Door mounted printer of VFD replaced. Problem solved.
FIELD LOSS 19. Tripping of ID Fan on field loss.
Self test failed.
Excitation system thoroughly checked. Found that in ch-2
the exciter output current was less due to non-conduction
of one thyristor. NHVL card changed. Channel cleared for
service after EVC power test and calibration.
One of the zener diode in IOMA Mother Board had
failed. Replaced and self test was passed.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 59 of 95
MISC 20. Vibration of motor current on ID Fan (sometimes in
the order of 80A). Output voltage waveform was
found distorted.
Output feedback CTs were found loose at the mounting.
Same tightened. NHVL card replaced.
Motor current vibrations still present.
Adjustment of speed regulator gain did not reduce the
variations. SFE of ch-1 to be replaced when shutdown
available.
Ch-2 configured as Master and ch-1 as Slave and Fan put
into service. Variations not observed.
Defective card brought to BHEL-EDN for repair.
MISC 21. Unbalance of 50A in the motor current between the
two channels of VFD.
Ch-1 current indication at the remote(UCB) was showing
less where as in the local, the current was showing
balanced because of problem with the V/I converter in
NLCB card. Same replaced.
Problem solved. Current for both channels were balanced
at the remote. Defective card brought to BHEL-EDN for
repair.
GROUND FAULT 22. When ID Fan started after cleaning for annual
maintenance, Ch-1 & ch-2 tripping on Ground fault at
a motor voltage of about 800VAC (300rpm). This
was observed on trials in single channel operation or
in dual channel mode.
During cleaning of the panels, customer has broken
connection at the lug points of the HV cables connecting to
the load side filter ckts. Cables recrimped. Problem solved.
LOAD
COMMUTATION
FAILURE
23. Channel tripped on Load Commutation Failure. 1. Check SEM earthing as per SEM Earthing document.
2. Change X(reactance) compensation resistors in
NLIB(1D) i.e. change R60, R68, R76 from 180K to
100K Ohms & check the 3 flux reconstructed
waveforms on NLIB(1D). Change resistors to lower
values (upto 33K Ohms) till the reconstructed
waveforms are sinusoidal.
3. Change LIMARG.
All the above done but problem not solved.
Intermittent tripping of channel between period of 4 hrs
to 48hrs observed.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 60 of 95
1. The load side thyristors, snubber ckt, CT ckt, gating
ckts thoroughly checked. All terminations on HPTK
and NTDA cards checked for loose connections and
soldered/tightened/replaced wherever required.
2. Self test & gate test conducted. Speed feedback
ckt found malfunctioning in NLCB /DLCB. DLCB
changed. Speed fdbk ckt calibrated.
3. Gating power supply changed from 89V to 91V.
4. Crowbar test s conducted. Current feedbacks O/C
protection ckt checked and adjusted wherever
required.
5. Channel put into service, Voltage and checked
waveforms checked and found normal.
Channel tripped again on “Load Commutation Failure”.
1. Firing pulses and the associated ckts of HPTK , XTFU
and the related ribbon cables checked.
2. In 2 of the HPTK cards on the load side, the
reference for detection of ‘undervoltage of gating
supply’ was 1.3V DC while in others it was 1.8V DC.
Reference adjusted to 1.8V DC in all HPTK cards.
Self test and gating tests conducted and all
parameters found normal.
Problem solved.
MISC 24. Ch-2 tripped. SEM Power supply PSFF found OFF. PSFF replaced.
Problem solved.
MISC 25. Ch-2 tripped. HMPG not getting reset. HMPG Bushog problem. HMPG replaced. Problem solved.
BRIDGE
DIFFERENTIAL
PRESSURE
26. Ch-1 tripped on ‘Bridge Differential Pressure’.
‘RSFM’ resistance found dry soldered. And
disconnected from ‘Tag board resistance card’.
Dry solder problem in Tag board. Soldering done properly.
Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 61 of 95
MISC 27. Ch-2 Current suddenly reduced to 220A. Berg Jumper J2 on DMPB defective. Replaced. OK.
GATING SUPPLY
DIP & LOAD
COMMUTATION
FAILURE
28. Ch-2 tripped on “gating supply dip, load commutation
failure, gating power supply loss”.
HPTK card of LTM4 burnt. HPTK card replaced.
HLCB card found failed. Replaced.
Problem solved.
SOURCE PLL
FAULT
29. Ch-2 tripped on ‘Source PLL Fault ’ Loose attenuation card connection in STM1.
LOAD
COMMUTATION
FAILURE
30. Ch-2 tripped on ‘Load Commutation failure’. Dry solder problem in NTDA card. Card replaced.
2 nos. HPTK card changed. HMPG found failed. HMPG
replaced. Problem solved.
GATING SUPPLY
UNDERVOLTAGE
31. Ch-1 alarm ‘Gating supply undervoltage’. NTRF card changed & channel started and channel tripped
on ‘Field loss’ problem.
Field exciter board NHVL changed. Problem solved.
Channel taken into service.
GATING SUPPLY
DIP
32. Ch-2 tripped on ‘Gating supply dip’. NTRF card failure on 70V power supply. NTRF changed.
Problem solved.
LOAD
COMMUTATION
FAILURE
33. Ch-2 tripped on “Load Commutation Failure”. 24V DC in PSFF found dipped. HROA(1B) having Motor
above minimum speed changed. Problem solved.
MISC 34. Source Breaker trips but no Alarm or Fault lamp or
any message on printer. Channel taken into service
after taking out the wires on IOMA Elmex TB
connecting to SWGR relay aux. contact.
Advised to change HROA relay card in IOMA module
which energises SWGR relay. This module will have
SWGRX relay on it.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 62 of 95
MISC 35. Gating tests and Exciter Power tests not passing in
Fan-B Ch-1.
HMPG card found to be the problem. U10 IC on the HMPG
cards found of Harris make.
HMPG cards replaced and Problem solved.
LOAD
COMMUTATION
FAILURE
36. Ch-2 randomly tripping on Load Commutation Failure. SEM Rack cleaned by blowing air. Channel taken into
service. OK.
GROUND FAULT,
LOAD
COMMUTATION
FAILURE
REV.04
37. Channel tripping on Ground Fault and Load
Commutation failure.
Channel Tripping on Ground Fault. Observed that neon
lamps across Load Bridge Thyristors also glow when Source
breaker is switched ON. Found ground fault in cable
connecting transformer secondary and Source bridge. This
was done after isolating cable at both ends using HV
megger and Hi-pot. Cable changed and Channel taken into
service.
Thereafter Channel tripping on Load Commutation failure
intermittently. Since all waveforms were OK, it was
inferred that the problem can be attributed to spurious
malfunction in electronic cards. NLIB(load) ,HLCB, HAIA
and Pulse distribution card XTFH changed. Problem
persisted. Grounding system of entire channel thoroughly
checked and re-inforced with additional cables from panel
earth strip to station earthing mat. Channel taken into
service. Problem solved.
MISC
R05, 1107, PH
38. Field Contactor chatters when Ch-1 (Master) is
paralleled to Ch-2 (Slave), with motor running
through Ch-2. No Fault or Alarm annunciation.
Since field contactor closes after Load Breaker closes,
aux. contact problem in Load breaker was suspected i.e.
MISOL input in IOMA changing from True to False to true
to false, even though breaker is closed.
Found contact resistance in aux. contact of Output Ckt.
Breaker not OK. Shifted wires to another contact.
Problem solved.
Formatted Table
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 63 of 95
LOAD
COMMUTATION
FAILURE
R05, 1107, PH
39. Slave (Ch-2) trips immediately after paralleling to
Ch-1.
Back-charged Ch-2. Found that voltages on NSFC Load
Unbalanced. Further found that one attenuator resistor in
R Phase load XTFH was open. Changed card. Ch-2 taken
into service. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 64 of 95
Category Sl.no. Problem Solution MISC 1. Ch-1 had problem of not starting. Gate pulses for Source and Load were checked and found
OK.
SEM cards were removed, cleaned and inserted in its
position.
2 lug connections at HPTK card were found to be loose and
were corrected.
Customer requested BHEL-EDN to supply spare lugs and
snubber mounting screws for fixing.
Trial run of Ch-1 was taken from Local control and
starting of fan was smooth. This was checked again for
repeatability and found OK.
MISC 2. Ch-2 not taking load when paralleled with Ch-1. Checked 12P11P and 12P11N connections on sheet 2BF.
Found OK.
Changed NLCB in Ch-2.
Paralleled OK and took load.
Cleaned original NLCB and replaced. Load taken.
Problem was due to dust on NLCB/DLCB.
MISC 3. Drive speed dipped below minimum and came to
MODE 2 when speed is lowered to minimum speed.
Changed SRGAIN in steps of 0.1 upwards and multiple
trials taken till satisfactory performance was observed.
Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 65 of 95
LOAD PLL FAULT 4. Ch-1 tripped on “Load PLL Fault”. Surge protective
arrestors of CT1,CT3,CT4 and CT6 which are
connected at TB3-01&02 got burnt and damaged the
CT wiring of CT1 & CT3.
1. Fan & Filter panel thoroughly cleaned.
2. Blowing done at C&EXE, Bridge panels.
3. Wiring checked at C&EXE, Bridge,Fan & Filter panels.
4. CT circuit checked for tightness.
5. Surge arrestors SD1, SD3, SD4, SD6 replaced. After
replacement, CT circuit checked for continuity and
links closing. Self test done and passed. Problem
solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 66 of 95
Category Sl.no. Problem Solution MISC 1. Some sounds and vibrations observed in the DC
reactor link between Converter and Inverter and
hunting in speed found. Tripping of Fan-B Ch-2
when voltage reached above 500 Volts.
XLPE Power Cable screen not earthed. Screen earthed.
Problem solved.
GROUND FAULT 2. Ground fault in both channels of Fan-B. Load side capacitors found faulty and neutral grounding of
R-C circuit was not O.K. Problem resolved.
GROUND FAULT 3. Ground Fault problem in Ch-2. Cable from contactor to motor was found faulty during hi-
pot test to earth. Faulty part of cable removed and joint
put. Problem resolved.
MISC 4. With Ch-1 tripped, Ch-2 not responding to speed
Raise command. Current and speed of ID Fan not
responding.
Parameter SRCLSC found to be 0.7 instead of 1.0.
SRCLSC changed to 1.0. Problem solved.
LOAD
COMMUTATION
FAILURE/SHORTED
MOTOR WINDING
5. Channel tripping with fault message “Load
Commutation Failure and Shorted Motor Winding.”
Firing pulse LED on one card in Source bridge
missing.
NSFC card changed and checking of all connectors and RC
Filters carried out. Power bridge on load side checked.
HPTF card on load side changed. Problem solved.
LOAD
COMMUTATION
FAILURE
6. Load Commutation Failure message received on
channel and thyristors produced hissing sound
during dry firing.
Voltage on the P70 module was measured and found to be
73 volts instead of 80 volts by adjusting the
corresponding pot. Problem solved.
SOURCE
OVERCURRENT
7. Source Overcurrent message received on channel.
Sparking found at the gland end of R phase at the
back side of the bridge panel.
Earthing of XLPE cable not found either on bridge end or
the transformer end. Earthing done on the transformer
end. Problem solved.
GROUND FAULT 8. Ground Fault message received on channel. Voltage at NTL port of NLCB card was measured and
found to be 0.51V instead of 0V. The cause was found to
be unbalance of current in the three phases. On
performing the megger and hi-pot test, it was found that
Formatted: Indent: Left: -0.13 cm,Right: -0.13 cm
Formatted Table
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 67 of 95
the ‘Y’ phase insulation had failed. The cable for ‘Y” phase
was replaced. Problem solved.
LOAD
COMMUTATION
FAILURE,
GROUND FAULT
REV.04
9. Slave channel trips during running, on Load
Commutation failure and Ground Fault.
Crowbar test conducted and found OK. Therefore Ground
fault suspected on load side. MOV and PT on Load
breaker checked, found OK. With Output breaker drawn
out, Motor AC voltage measured with respect to earth by
Motwane multimeter in High voltage range. Great care was
taken when doing this. Voltage unbalance found. Motor
stopped. Cable fault found between Motor and Output
breaker after Hi-pot test. Note that Megger value of
failed cable was OK. Fresh joint made. Channel taken into
service. Problem solved.
SOURCE
COMMUTATION
FAILURE
REV.04
10. Source Commutation failure occurs when channel is
taken into service.
Crowbar test conducted, but channel tripped on Source
Commutation failure. AC side line filter capacitor checked
and found OK. Attenuated voltages on Source NSFC and
FAB,FBC,FCA on Source NLIB found OK. HLCB changed.
Problem persisted.
Cable connections from transformer secondary to panel
removed. Meggered transformer and found OK. Meggered
cable and found OK. Finally, XLPE HT cable earthing braid
from transformer to panel was found loose. Connection
tightened. Problem solved.
LOAD PLL FAULT
R05, 1106, VI
11. Drive trips on Load PLL Fault once in a while but
period of tripping is regular.
Found that panel was not earthed. Earthed the panel from
ground bus at rear at both ends. Completely cleaned the
panel by air blowing. Checked all connections in Load side
filter RC circuit and MOV. Some of the bleeder resistors
across filter Capacitor leads were very close to the
capacitor case. Made these resistors lead vertical.
Channel taken into service. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 68 of 95
Category Sl.no. Problem Solution MISC 1. Source breaker getting tripped immediately after
closing. Overvoltage lamp on NLIB card found
glowing.
Overvoltage setting in NLIB card changed as per scheme.
Problem solved.
MISC 2. Speed and voltage not increasing at 35 Hz and
current swinging. Pump not attaining full speed.
INVLIM getting set at 2304 & 288.
DC Offset voltages at NLIB FAB, FBA & FCA was
1.0Volts DC, when no voltage was present on Source
bridge or Load Bridge. Adjusted NLIB (L) Offsets to
zero. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 69 of 95
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 70 of 95
Category Sl.no. Problem Solution MISC
R05, 0906, PH
1. Cannot parallel Slave channel with Master at min.
speed. Current in slave does not rise. Tune-up
parameters in both channels OK. Running of motors
in individual channels OK.
Master channel run at minimum speed. Back-charged slave
channel and adjusted offset zero on Load NLIB FABR,
FBCR, FCAR. Also adjusted values of FAB, FBC,FCA on
Load NLIB same as in Master, taking master as reference.
Put slave channel into service. Problem solved.
MISC
R05, 0207, PH
2. Channel-1 Master running. But when Slave channel is
paralleled with Master and speed is raised, Slave
channel current remains at minimum.
12PII (Torque Reference) +/-10 Volts analog from IOMA
Ch-1 to IOMA Ch-2 not connected correctly. It should be
noted that this connection is polarity sensitive.
Wires connected correctly.Channel taken into service. OK.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 71 of 95
Category Sl.no. Problem Solution MISC
R05, 1206, PH
1. Communication with Laptop PC stops. Originally OK. Changed HMPG card. Problem remained. Changed HLCB
card. Problem solved.
GROUND FAULT
R05, 1206, PH
2. Motor starts and runs upto minimum speed. As soon
as it reaches LMODE=3, channel trips on Ground
Fault. Motor voltage at this instance approx. 400V.
Other channel was not available to check this fault by
backcharging.
Connected a 415V Source to Inverter Output. Found Line
to Neutral voltages unbalanced. Isolated Load side RC and
MOV circuits. Found Line to Neutral voltages balanced. On
further investigation, it was found that brazing on one of
the load side RC filter resistor had opened. Resistor
replaced. 415V applied. All line to neutral voltages found
balanced. Channel taken into service. No ground fault trip
observed. Problem solved.
GROUND FAULT
R05, 0507, PH
3. Channel trips on Ground Fault when speed reaches
over minimum speed. Other channel not
commissioned. Therefore, back-charging not
possible.
Fed 415V 3ph 50Hz from Auto-transformer to Load side
busbars R,Y,B in channel, with output VCB in OFF
condition. Found unbalance in FAB, FBC, FCA in NLIB-
Load. Removed cable from DC Reactor to Load side
negative and also P1-P2 jumper busbar connecting Load
and Source side bridges. Unbalance on FAB,FBC,FCA
remains. Isolated Load side MOVs. Unbalance remains.
Found that connection to Y ph R-C circuit resistor
terminal wire cut-off. Replaced the wire wound resistor.
Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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Category Sl.no. Problem Solution MISC
R05, 1006, VI
1. All 4 channels of the 2 ID Fans give problems during
starting. Starting not smooth. Heavy oscillations of
current/source and load overcurrent during
starting.
During crowbar in all channels, high overshoot was
observed in IFB source current. There was no change in
overshoot by changing CRALPH1 & CRALPH2. Peak of
overshoot was reduced if SMARG was increased.
By Load NSFC SIG waveform it was ascertained that the
Load thyristor module gave the overshoot. Corresponding
module swapped from Source bridge. Conducted crowbar
test. No overshoot observed. Trials were taken and
starting was found to be smooth. Problem solved.
LOAD PLL FAULT
R05, 0207, VI
2. Slave channel current oscillates at higher load and
this happens whenever the current demand is
greater than 50%. Sometimes the channel trips on
Load PLL fault. INVLIM sets to 4096 sometimes
during the period when current oscillations occur.
During this time the Master channel current is
steady.
Found that NLIB Source and Load cards were
interchanged. This was done after all the checks referred
as given in Annexure for this fault.
Interchanged the cards. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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Category Sl.no. Problem Solution LOAD
COMMUTATION
FAILURE
R05, 1106, VI
1. Slave channel FanB Ch-2 trips on Load Commutation
Failure after certain speed.
Observed that below tripping speed Load side feedback
0IA was missing. Found that links on CT shorting
terminals were loose on CATDM4 TBs. Tightened the
same. Problem solved.
MISC
R05, 1106, VI
2. After certain speed, slave channel current oscillates
but master channel current remains steady.
INVLIM does not set during this time in slave
channel.
Found Load side CT phasing of 0IC is not OK. Corrected
the same by reversing the Secondary terminal
connections. Problem solved.
I/O ADDRESSING
PROBLEM
R05, 0407, PH
3. Channel running normally. Trips sometimes on I/O
Addressing problem. With this, other IOMA Input
faults like Fan Compartment door open are also
displayed. BUSHOG LED on HMPG does not come
ON.
Changed all ’H’ cards in SEM HAIA, HLCB, HRDA one by
one. No change observed. Changed HMPG but retained
DMPB. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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Category Sl.no. Problem Solution GROUND FAULT
R05, 0207, PH
1. Slave channel trips on Ground Fault when paralleled
with Master.
Backcharged Ch-2(Slave). Found that one load side
feedback voltage at Load NSFC 2B was not OK. Found
one resistor of the attenuator resistor network was open
in LTM2 HPTK. Changed HPTK. Problem solved.
MISC
R05, 0707, PH
2. During exciter test current is unbalanced. But when
exciter output is connected to a dummy load, the
R,Y,B currents are balanced.
The Stator resistance of the exciter (each phase) was
equal. But when measuring the inductance of each stator
phase of exciter, the values were different. Found that
the start and end of one phase of exciter rotor star
winding was connected wrongly. Changed the connection.
Conducted exciter test. Currents balanced. Problem
solved.
It is inferred that during exciter test, if the shaft of the
motor was moved to different positions, the exciter
current imbalance would have shifted from one phase to
another.
MISC
R05, 1107, PH
3. Source breaker trips without any alarm or fault
annunciation. Trip is from IOMA SWGR relay. Trips
occur spuriously. No pattern i.e random.
Changed HRDA and HROA. But problem persisted.
Observed that in HRIA inputs low level DC voltages are
present even though input contacts to HRIA open –
Suspected backplane board problem. Complete IOMA
module changed. Channel taken into service. Problem
solved.
MISC
R05, 1107, PH
4. Output circuit breaker trips without any alarm or
fault being annunciated. Trip is from IOMA RUN
relay. Trips occur spuriously. No pattern i.e random.
Checked the auxiliary contact of Load side circuit
breaker. Operation and change of MISOL input is OK.
Observed that in HRIA inputs low level DC voltages are
present, even though input contacts to HRIA open.
Suspected backplane board problem. Complete IOMA
module changed. Channel taken into service. Problem
solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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Category Sl.no. Problem Solution MISC
R05, 0907, PH
1. Channel was in service and running OK. After
shutdown while starting, Fan speed reaches minimum
speed but LMODE remains at 1. Also does not
parallel with other channel over minimum speed.
Gate test mode OK. Crowbar test OK. Back-charged over
minimum speed. Load FAB, FBC, FCA values were same as
other channel.
MTRFMIN and FLUXS Lowered by 0.1. LMODE=1
changed to LMODE=3. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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Category Sl.no. Problem Solution LOAD
COMMUTATION
FAILURE
R05, 0107, PH
1. When channel is run individually, speed does not
raise. Current hunting is observed and channel trips
on Load commutation failure.
During current hunting INVLIM was being set to 1.
(Source-load differential). Found CT phasing on Load side
was not OK. Corrected the same.
Drive started and found that IFB Source and IFB Load
DC Volts on NLIB Source and Load not equal. Adjusted
XTFX CT burden resistor potentiometers to make CT
burden on load side equal to that of the source. Channel
started and resumed trials. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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Category Sl.no. Problem Solution MISC
R05, 0307, VI
1. Motor takes very longtime to start. During starting period, it was observed that firing pulses
to STM1 were not present as LED on HPTK STM1 not
glowing. Replaced HPTK on STM1. Problem solved.
MISC
R05, 1007, PH
2. When START command is given from Remote,
Output CB closes but opens after 3 to 4 seconds.
Checked whether RUN command from Common Control
panel was ON. Found OK. Put clip on 220V Jyothi relay in
VCB. No change. Suspected HRIA card RUNX relay 1BH49
not working. Swapped HRIA card 2A & 2B. Problem solved.
MISC
R05, 0607, VI
3. Master and Slave do not share equal current when
paralleled. When speed is raised, heavy oscillations
occur in Slave (Ch-2).
Found that in IOMA TB07/10,11, the polarity of current
reference going to Slave (Ch-2) was negative instead of
positive (Motoring condition). Changed NLCB card in
Master. Problem solved.
LOAD
COMMUTATION
FAILURE
R05, 1107, VI
4. When drive runs on single channel and higher speed
and load, Load commutation failure occurs after
three hours approximately.
All tests as given in Annexure of Compendium already
done, but problem persists. The 180K resistors on NLIB
load R60, R68, R76 for XL compensation of motor
changed from 180K to 100K. Channel taken into service.
Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 78 of 95
Category Sl.no. Problem Solution MISC
R05, 0707, PH
1. When channel is run individually, current hunting
takes place. INVLIM does not set to any value and
remains at zero continuously. There was light
hammering sound in the motor.
Since INVLIM does not set to any value, it was inferred
that the problem would be in the excitation circuit. Did
exciter test. Excitation currents balanced. Motor was
thoroughly inspected. Condition found OK. It was thought
that the sound in the motor could be due to sudden
change in the magnetic centre during running. Excitation
IFB waveform on NSFE checked when running. Found
that sometimes the waveform was getting disturbed.
Changed NSFE card slot 2E. Problem solved.
GROUND FAULT
R05, 1207, PH
2. Channel gives Ground fault during crowbar. But,
when back-charged from other channel, ground fault
does not occur. Channel is 2.3kV LCI.
Checked MOV, RC circuits on Load & Source side and also
DC Link Source/Load. All found OK. All earthing checked
and found OK.
Crowbar was performed with 415Volts (earthed supply) on
Load & Source bridge separately, by swapping NSFC
connectors on Source/load and current feedback ribbon
cables on SEM header, when during Load side crowbar,
only 3 resistors in XPTN put in circuit. Ground fault
occurred in both instances of Source & Load crowbar.
While doing this test with isolated 415Volts supply,
Ground fault did not occur. It was suspected that the
problem could be only on Source side circuit between
Transformer and Source bridge. When cables were hi-
potted, Y phase cable gave fault w.r.t ground after 2.5kV
AC. Examined cable and found at one location insulation
was slightly damaged. Cable changed to new. Conducted
crowbar test. OK. Channel taken into service. Problem
solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
Page 79 of 95
Category Sl.no. Problem Solution GROUND FAULT
R05, 1207, PH
1. Channel gives Ground Fault during Crowbar test. No
ground fault when back-charged with 415V 3ph from
Load side and with only 3 resistors shorted on load
and source HPTF. Channel is 1.2kV LCI. Other
channels not available for back-charging.
It was inferred from the 415V back-charging that the
ground fault will be on the source side. Checked RC circuit
and MOV circuit on Source side. Found that star point of
Source MOV was earthed, instead of the earth being
done from the fourth MOV. Changed the connection as
per scheme. Crowbar performed OK. Problem solved.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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GENERAL CHECKS:
1. Check thyristor gate pulses in Gate test mode.
2. Check thyristor and snubber healthiness.
3. Check healthiness of load, source and DC circuit capacitors, MOVs.
4. Check passing of Self test .
5. Conduct crowbar test and get OK results. During crowbar the voltmeter on C&EXE panel should show zero volts and must be
steady at that value. Also Source phase currents must be clean without any spikes.
6. Conduct Megger test on complete power circuits from transformer upto motor. 7. Remove motor inspection cover. Check healthiness of windings w.r.t. earth, between windings.
8. Check CT /PT feedback circuits.
9. Ensure proper earthing of SEM Rack by removing paint at various points.
10. All connections including busbars, connectors, wires, crimped terminals are to be checked for tightness. Ensure SEM Lock bar is firmly in place.
11. All electronic cards, thyristor power modules, air filters are to be blown with clean air to remove dust.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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CHECKS FOR GROUND FAULT , LOAD COMMUTATION FAILURE, LOAD PLL FAULT :
1. Check SEM earthing OK.
2. Back charge Ch-1 from Ch-2 by tripping Ch-1 source breaker and locking it out. Then close output contactor by shorting IOMA
TB8 after removing RUN relay from IOMA plug-in base. Check the waveform of attenuated voltages at NSFC Load and Flux
waveforms at NLIB-load. Check the waveform at NTL on NLCB . Ground fault occurs if NTL > 0.55V DC.
3. Check capacitors on load side by meggering with 1000V or 500V megger across its terminals & also w.r.t ground. Discharge
capacitors by using the 20M, 2W resistor on the DC capacitors or any suitable rheostat. Check capacitance values of Load side
capacitors by LCR bridge. 4. Remove end covers on the panels and check that the earth bus is continuous from C & EXE. Panel to ACOP panel. If earth bus is
broken in between the panels, bridge this connection with 25sq.mm Cu cable. Also check the JL solder stud on XTFL-Load is firmly
soldered and the wire from this point firmly connected to the earth bus running on the rear of the panels. Ensure that SEM
ground gives proper continuity with this stud. 5. Hi-pot to earth cables from motor to Output Contactor /Breaker after removing both ends of cable. Hi–pot voltage can be
restricted to the voltage, at which ground fault occurs.
6. Check load connection in load side MOV and load side RC filter circuit. Check healthiness of fuses on this circuit.
7. Check values of variable components in SEM cards as per Schematic diagram. Formatted: Bullets and Numbering
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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Annexure-1: EARTHING FOR SEM RACK
S S S N
S
CARD N Aluminium
SLOTS Extrusion
Aluminium
N Extrusion Z
CARDS GND
SLOTS N
SEM FRONT Y
VIEW Cu. Braid
Remove only one Nut/Bolt at a time. Check Spring/Plate washer present
1.Remove paint on both sides of Nut/Bolts marked ‘N’.
2.Remove paint on Nut side of ‘S’ and lacquer on PCB board track(if lacquered) on Head side of ‘S’.
Test with mulimeter if in doubt. Generally this mother board will not be lacquered.
3.GND is tinned copper ground bus in C & Exe Panel (Regulation panel in high current rectifier) .
Make connection ‘Y’ at site(if not already present) with 25-sq. mm. Aluminium or copper cable with lugs on
both sides. Check if ‘Z’ cable copper/PVC already exists. If not make connection ‘Z’. Cable ‘Z’ is 16 sq.mm.
Copper braid/PVC cable, connection may already done at BHEL/EDN in Panel.
Front Back Front Back
CCC
SEM SIDE SEM SIDE SEM BACK
VIEW VIEW COVER
4.Scrape paint on both sides on plate of nut/bolt ‘A’ and ‘B’. Exercise caution as the motherboard
pins may get bent accidentally when doing this.
5 Scrape paint on back cover on head side of screws’C’.
6.The objective of these points 1 to 5 is to ensure that PCB(mother board) ground track mentioned in
point 2 is perfectly connected to tinned copper earth bus in C & Exe, panel(Regulation
Panel in high current rectifier).
7. All Nut Bolts to have spring and plate washers. Only plated washers to be in contact with paint
scraped surfaces only. Replace if biting/toothed washers are present. Replace one at a time.
8. Check that the PCB motherboard pins have not been bent.
9. Re-check all points 1 to 8 above have been done. Check for continuity between ‘S’ and ground
copper flat.
10.Install SEM back cover carefully.
A
A
A
B
B
B
C C
C C
C C
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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Annexure-2: DETAILS OF FT1 AND FT2 INDICATION ON LED BAR
IN NLCB CARD
FT1
UNLATCH
ISTLINHB FT1
RESET
SUPP(S)
OSFT1
FT2
10SP FT2
SUPP(L)
OVA(L) FLT(SWRE)
FT1 AND FT2 are the first two LED’s seen from the top on the BAR LED of NLCB with
inscriptions of FT1 and FT2 respectively.
1. Description of FT1:-
The logic for the LED FT1 being ON is as given in the diagram above.
When the FT1 LED turns ON it also closes the SWGR relay in the IOMA to trip the source
breaker, if it is closed or if the source breaker is closed the permissive to close is lost.
FT1 is turned ON in case of major faults. They are the Hardware Source over-current,
Microprocessor stall (µP stall) and System Fault (Not(NSFLT)) as detailed below.
a) Hardware Source over-current (SUPP(S)) :- The currents from the 3-phase of the
source side obtained through CT’s are rectified in the analog boards to obtain a DC
current feedback IFB which is compared in the source NLIB board with the SUPP
settings to initiate source over current after 25ms.A source over current has occurred
and it persists for a period of more than 25ms. The message in case of this condition
is “Source back up over current fault”.
STALL
INHIBIT
OR
RD
OR
RD
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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b) Microprocessor stall (µP stall): To detect software malfunctioning and Software code
runaway a hardware circuit is built consisting of a tickle timer in Monoshot mode. In
the event the software does not regularly reset this timer as the software has run away
or in the case of malfunction this timer generates a stall signal.
c) System Fault (Not (NSFLT)): - Please see the Ladder logic in sheet 1FE of the LCI
scheme. This is declared under any of the following conditions: -
a. Source current imbalance. (Series 12 pulse only)
b. Source over-current.
c. Loss of cooling fan.
2. Description of FT2: -
The logic for FT2 led to turn ON is as given in the diagram in previous page. When the FT2
turns ON the fault relay IOMA also closes. Thus a fault is annunciated.
FT1 is turned ON in case of Over-speed (1OSP), Load Over current (SUPP (L)), Load over
voltage (OVA (L)) and Channel fault (NOT (NCFLT)) as detailed below.
a) Over speed (1OSP):- The speed feedback is obtained by the hardware circuit on the
NLCB from the voltage waveform of the load side. When this speed signal exceeds
the setting of OSP on the NLCB then this is actuated.
b) Load Over current (SUPP (L)): (Load backup over current fault) The currents from
the 3phases of the load side obtained from CT’s are rectified in the analog boards to
obtain a DC current feedback LIFB which is compared with the SUPP setting on the
load NLIB board to initiate load over current after 25ms. The message in this
condition is the “Load backup over current fault”.
c) Load over voltage (OVA (L))( Load AC over voltage): - The 3∅ voltages of the load
side are attenuated and available at the input of the load NLIB boards. The analog
board has a rectifier circuit converting these AC voltages to DC. This DC voltage is
compared with the OVR setting of the load NLIB board and when greater initiates a
load over voltage fault.
d) Channel fault (NOT (NCFLT)): -The NCFLT is as per ladder logic on sheet 1FE of
LCI schematic diagram. The Channel fault is declared when a hardware or software
fault occurs in the drive as per the logic in sheet 1FE.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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Annexure-3: Details of Fault and Alarm Messages in the LCI Drive
FAULT MESSAGES: -
1. LOSS OF COOLING FAN : -
Please refer ladder logic sheet no 1FK
LOGIC = NOT (NBLF)
2. SOURCE LOW LINE
Please refer ladder logic sheet no 1FK
LOGIC = SUVFLT
3. FIELD LOSS
Please refer ladder logic sheet no 1FK
LOGIC = FLD_LOSS_FLT
4. SOURCE BACKUP OVERCURRENT FAULT Please refer ladder logic sheet no 1FK
LOGIC = SRC_SUPP
INPUT = PORT 900C BIT 2
5.LOAD BACKUP OVERCURRENT FAULT Please refer ladder logic sheet no 1FK
LOGIC = LD_SUPP
INPUT = PORT 900C BIT 5
6.SOURCE OVERVOLTAGE FAULT Please refer ladder logic sheet no 1FK
LOGIC = SRC_OV
INPUT = PORT 900C BIT 0
7.GATING SUPPLY UNDERVOLTAGE FAULT Please refer ladder logic sheet no 1FK
LOGIC = GSUV
8.P105 SUPPLY UNDERVOLTAGE Please refer ladder logic sheet no 1FK
LOGIC = NOT (NPSUV)
9.LOAD OVERVOLTAGE FAULT Please refer ladder logic sheet no 1FK
LOGIC = LD_OV
INPUT = PORT 900C BIT 4
10. OVERSPEED
Please refer ladder logic sheet no 1FK
LOGIC = OS
INPUT = PORT 900C BIT 7
11.GROUND FAULT
Please refer ladder logic sheet no 1FK
LOGIC = GNDF
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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INPUT = PORT 8010 BIT 0
12. FAN COMPARTMENT DOOR OPEN Please refer ladder logic sheet no 1FK
LOGIC = NOT(BFNDR)
13 .BRIDGE DIFF PRESSURE
Please refer ladder logic sheet no 1FK
LOGIC = BFDIFSW
14. FIELD CURRENT IMBALANCE: - FLTWD BIT 0
Field current imbalance check is for AC exciter only.
If a field current imbalance is detected by the NSFE card and persists for more than 0.5 sec then a fault is declared.
15. FIELD OVERCURRENT :- FLTWD BIT 1
If field current exceeds “FCLIM” for the no of attempts given by “ FCFTIME” then the fault is declared. A penalty
function is implemented such that 6 good firings following a failure will cancel a fault firing. This allows recovery from
non repetitive faults.
16. SHORTED MOTOR WINDING :- FLTWD BIT 2
During a start up from standstill, when the motor speed has exceeded the value set by “TRSPD” and the Load PLL is
locked. Then the peak flux reading taken at every 60 deg electrical from the machine (obtained from integration of load
voltages from NLIB Load card) exceeds its previous value set by “SWINDTOL”(approx 10%). Then a Shorted Motor
Winding Fault is declared. The shorted phase can be obtained from the variable Shorted winding in ENGG mode.
17.SOURCE OVERCURRENT: - FLTWD BIT 3
If source current exceeds “LKLIMS” for the no of attempts set by “LKOCTIM” then the fault is declared. A penalty
function is implemented such that 6 good firings following a failure will cancel a fault firing. This allows recovery from
non-repetitive faults.
18.LOAD OVERCURRENT : - FLTWD BIT 4
If source current exceeds the limit set by “LKLIML” for the no of attempts given by “LKOCTIM” then the fault is
declared. A penalty function is implemented such that 6 good firings following a failure will cancel a fault firing. This
allows recovery from non-repetitive faults.
19. SOURCE COMMUTATION FAILURE : - FLTWD BIT 5
During normal running of the drive, if the difference between the source and load current (read in synchronous with load
frequency cycle) exceeds the limit set by “LKLIMD” for the no of times set by “STHRUTIM” then a fault is declared.
A penalty function is implemented such that 6 good firings following a failure will cancel a fault firing. This allows
recovery from non-repetitive faults.
20.LOAD COMMUTATION FAILURE :- FLTWD BIT 6
During normal running of the drive, if the difference between the source and load current (read in synchronous with
Source frequency cycle) exceeds the limit set by “LKLIMD” for the no of times set by “STHRUTIM” then a fault is
declared. A penalty function is implemented such that 6 good firings following a failure will cancel a fault firing. This
allows recovery from non-repetitive faults.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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21.SOURCE PLL FAULT:- FLTWD BIT 8 The Source voltages are attenuated thro attenuator boards , conditioned in the firing card NSFC and then integrated in the
NLIB boards. These integrated signals are used for synchronization to fire the source bridge thyristors.
Software/Hardware Phase Locked Loop (PLL) does the synchronization.
If this synchronization is lost and remains as such for a period set by “SPLLTIM” then a fault is declared.
22.LOAD PLL FAULT:- FLTWD BIT 9
The Load voltages are attenuated thro attenuator boards , conditioned in the firing card NSFC and then integrated in the
NLIB boards. These integrated signals are used for synchronization to fire the source bridge thyristors.
Software/Hardware Phase Locked Loop (PLL) does the synchronization.
If this synchronization is lost and remains as such for a period set by “LPLLTIM” then a fault is declared.
26. FIELD OVERVOLTAGE FAULT:- FLTWD BIT 10
In Case The Exciter is DC. The field DC voltage is obtained through attenuators and the NSFF circuit. The NSFF circuit
has a over voltage detector (OOV) with fixed set point. When the field DC Voltage exceeds the limit the OOV sends a
signal and the Fault is annunciated.
23. STACK FAULT :- FLTWD BIT 11
The processor because of extraneous reasons may run away and may do unintended tasks very frequently In such cases
the STACK builds up. It is necessary to declare a fault in such cases.
24. FAILURE TO START :- FLTWD BIT 12
During start the speed regulator is open looped and the current command is fixed. The current command is ramped from
minimum current to a value required until motion is detected. Current reference ramps until the drive position has
changed 120 electrical degrees to maximum value of CUR_REG_REG_STRT_E. Motion is detected by looking for a
two cell pair change in the load side firings. If motion is not detected even after 5 secs then a fault is declared.
25. EEPROM TRANSFER FAILURE:- FLTWD BIT 13
The tunes up constants are stored in the EPROM of HMPG the Processor Board, during running of the drive these
constants are loaded in to the EEPROM for operation. If there is a problem in this operation during initialization then this
fault is declared.
26. MOTOR ISOLATOR NOT CLOSED Please refer ladder logic sheet no 1FK
LOGIC = MISOL_STATUS_FLT
27. TACH FEEDBACK OR HTCA PROBLEM
This fault is only in Drives using Tacho feedback with HTCA card. When the HTCA card or the tacho malfunctions then
this fault is declared.
28.SOURCE MASTER/SLAVE CURRENT UNBALANCE
29. SLAVE HARDWARE OVERCURRENT
The above two faults are declared in case of series 12 Pulse.
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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ALARM MESSAGES: -
1.MOTOR OVERTEMPERATURE Please refer ladder logic sheet no 1FK
LOGIC = NOT(MOVTEMP)
2.TRANSFORMER ALARM
Please refer ladder logic sheet no 1FK
LOGIC = NOT(TTRBLE)
3.LINK REACTOR OVERTEMPERATURE
Please refer ladder logic sheet no 1FK
LOGIC = NOT(LTRBLE)
4.PCR OVERTEMPERATURE Please refer ladder logic sheet no 1FK
LOGIC = NOT(PCROT)
5.USER DEFINED ALARM Please refer ladder logic sheet no 1FK
LOGIC = NOT(USERA)
6.COOLING BLOWER LOSS Please refer ladder logic sheet no 1FK
LOGIC = NOT(NBLA)
7.BRIDGE FILTER FUSE BLOWN
Please refer ladder logic sheet no 1FK
LOGIC = NOT(BFILF)
8.RUN PERM OR START PERM MISSING
Please refer ladder logic sheet no 1FK
LOGIC = RUNPM, STRTPM
9.GATING SUPPLY DIP
Please refer ladder logic sheet no 1FE
LOGIC = GSUV_ALM
10.FIELD EXCITER VOLTAGE LOSS:- ALA BIT 0 01H
During start when the field is energized and the field voltage is built and present but its value is lower than required then
this alarm is declared.
11.ROTOR POSITION START ALARM ALA BIT 1 02H
During run If the motor fails to start within 1 sec from start, then this alarm is declared. The rotor position is determined
from relative flux amplitudes.
12.I/O ADDRESSING PROBLEM ALA BIT 2 04H
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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The Processor is sending and receiving data from various boards within the SEM Rack. If the response of the Board
exceeds a given time then this alarm is activated.
13.MICROPROCESSOR ALARM ALA BIT 3,4, 5,6,7.8.9.10
The Processor switches tasks by means of interrupts. This alarm is activated when the processor receives unintended
interrupts.
14.SOURCE UNDERVOLTS ALA BIT 12 02H
If the Source breaker is energized, and the source NLIB indicates a Source under voltage condition then this alarm is
declared.
15.FIELD THERMAL OVERLOAD ALA BIT 13 02H
The field thermal model when enabled, checks the field current with time and declares an alarm if the current has
exceeded its time limit.
16.LOSS OF SPEED REFERENCE ALA BIT 14 02H
The drive remote reference will have value between 4 to 20 mA. If the reference falls below a value of 4 mA then this
alarm is activated.
17.LOSS OF SPEED CONTROL
During the drive operation in Self-commutation mode, if the difference between the Speed reference and the Speed
feedback to the Speed regulator exceeds the set parameter “SRETOL” for a time settable by “SQTMR5” then an alarm is
declared.
18.FIELD GROUND ALARM DC Exciter only.
A ground fault detector circuit is part of the NSFF Card on the SEM rack. This circuit detects grounds, which may occur
at the output of the Excitation module. This alarm is annunciated whenever this circuit is activated.
19. TACH FEEDBACK/HTCA PROBLEM
This Alarm is only in Drives using Tacho-feedback with HTCA card. When the HTCA card or the tacho malfunctions
then this alarm is declared.
STATUS MESSAGES: -
To accommodate drives which run multiple motors of different ratings a tune up variable “MOTSEL” is
available. (a set of drive constants for every motor is stored separately ).
1. MOTOR TABLE 0 SELECTED
This Message is annunciated when the first motor is selected.
2. MOTOR TABLE 1 SELECTED This Message is annunciated when the Second motor is selected.
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Rev.04
Annexure-4: Procedure for conducting Crowbar test with other channel in
service in 12 Pulse drives
Crowbar test can be conducted on either Master or Slave channel with the other channel running.
On the channel on which crowbar test is to be done remove the following wires:
a. IOMA TB5/09 Other channel running
IOMA TB5/10 Sht 1BD/2BD grid 61
b. IOMA TB7/10 Current reference to other channel
IOMA TB7/11 Sht 1BF/2BF grid 55
c. IOMA TB2/15 This channel running/RTPOS
IOMA TB2/02 16 Sht 1BG/2BG grid 5161
d. IOMA TB7/16 Current reference into this channel
IOMA TB7/17 Sht 1BF/2BF grid 67
e. Remove and put insulation tape on wires. Connect wires back in the same TB after
finishing Crowbar test.
f. Ensure Load side Breaker/Contactor does not close by switching OFF supply in
Breaker/Contactor. Short MISOL input at IOMA TB4/05 and TB4/06 Sht 1BD/2BD
grid 21. Remove this short after Crowbar test.
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Rev.04
Annexure-5: Procedure for Backcharging of one channel in 12 Pulse drives with
the other channel of the same motor in service
a) Rack out the Source 6.6kV/11kV breaker for the channel which is to be back-charged.
b) Remove RUN relay from its base on IOMA module.
c) Short IOMA TB8/05 & TB8/06 Sht 1BJ/2BJ grid 23 momentarily. The load side
Breaker/Contactor closes and stays closed.
d) Motor voltage feedback is now available on NSFC load and Motor flux on NLIB Load.
e) Trip Output Breaker/Contactor by momentarily shorting IOMA TB8/07 and TB8/08 Sht
1BJ/2BJ grid 29.
The load side Breaker/Contactor opens.
f) Put RUN relay back on its base in IOMA module.
g) Rack in Source breaker 6.6/11kV.
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R05
Annexure-6: Procedure for Conducting Exciter test on one channel in 12 Pulse
drives with the other channel in service
Exciter Test can be conducted on either MASTER or SLAVE channel with the other channel
running by connecting a dummy load consisting of Lamps and Resistors at the output of Exciter
bridge.
In the channel on which Exciter test is to be done, remove the following wires:
a. IOMA TB5/09 Other channel running
IOMA TB5/10 Sht 1BD/2BD grid 61
b. IOMA TB7/10 Current reference to other channel
IOMA TB7/11 Sht 1BF/2BF grid 55
c. IOMA TB2/01 This channel running
IOMA TB2/02 Sht 1BG/2BG grid 51
d. IOMA TB7/16 Current reference into this channel
IOMA TB7/17 Sht 1BF/2BF grid 67
e. Remove and put insulation tape on cables R,Y,B at the output of field exciter
and also in wires (a) to (d) above.
Connect the dummy load to Exciter bridge output. Perform Exciter test.
Connect the cables on the Exciter and wires on the IOMA TBs back in the same positions
before removal. Extreme care to be exercised while doing this test. Switch OFF circuit breakers and
power supplies whenever required.
Formatted: Indent: First line: 0 cm,Outline numbered + Level: 2 +
Numbering Style: a, b, c, … + Start at:1 + Alignment: Left + Aligned at: 1.27cm + Tab after: 1.9 cm + Indent at:
1.9 cm
Formatted: Indent: First line: 0 cm,
Outline numbered + Level: 2 +Numbering Style: a, b, c, … + Start at:1 + Alignment: Left + Aligned at: 1.27cm + Tab after: 1.9 cm + Indent at:
1.9 cm
Formatted: Indent: First line: 0 cm,
Outline numbered + Level: 2 +Numbering Style: a, b, c, … + Start at:1 + Alignment: Left + Aligned at: 1.27cm + Tab after: 1.9 cm + Indent at:
1.9 cm
Formatted: Indent: First line: 0 cm,Outline numbered + Level: 2 +Numbering Style: a, b, c, … + Start at:1 + Alignment: Left + Aligned at: 1.27
cm + Tab after: 1.9 cm + Indent at: 1.9 cm
LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS
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