Post on 06-Sep-2018
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VFD Predictive and Preventive
Maintenance
Instructor: Trey Mayfield
tmayfield@emainc.net
www.emainc.net
Predictive Maintenance
Variable Frequency Drive (VFD)
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Device used to vary the speed of a driven load, such as pumps,
blowers, compressors, conveyors, punch presses, etc. to exactly
match the process requirements & achieve energy savings too
Includes built-in overload protection (no heater elements
required). Adjustable to the motor rated
current. Speed & non-temperature
dependent
Adjusts both the frequency
& voltage to the motor
Reduces the inrush current to
150/115% CT/VT (adjustable) of the
motor rated current
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SafetyThe most important thing to keep working is You!
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Familiarity with ElectricityIs NO Protection!
Skilled Electricians can be electrocuted as well as anyone else!
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Safety Rules
Lock it out!Tag it out!And still measure it Prior to touching it!
Per IEEE, the failure rate is 3times higher for electrical systems
that are not subjected to a regular PM program!
IEEE statistic on PM
Preventive Maintenance
Loose Connections 30.3%
Moisture 17.4%
Line Disturbance 10.4%
Defective Insulation 9.9%
Lightening 8.1%
Foreign Objects 7.3%
Collision 3.9%
Overloading 2.4%
Dust, Dirt, Oil 2.2%
All other causes 8.1%
What Causes
Failures?
Preventive Maintenance
According to IEEE, electrical systems that are not subjected to Preventive maintenance are
three times more likely to failure than those that are subjected to PM.
What does a PM Program Entail?
Qualified Personnel
Regularly scheduled inspection, testing, and
servicing
Evaluating Results
Work Performance
Record Keeping
Preventive Maintenance
Qualified Personnel
Properly trained on
specific equipment
Trained in Safety
procedures
Special training for
Medium voltage
Preventive Maintenance
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Regularly scheduled Inspection, Testing, and Servicing
Visual, thermographic, or other non-invasive inspections prior to
shutdown
All circuit breakers/disconnects repeatedly opened and closed
to insure proper operation
Protective Relays and Devices tested and calibrated
Test oil samples from all oil filled equipment (transformers)
Electronic equipment inspected, cleaned, and tuned
Preventive Maintenance
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Evaluating Results
The Person doing the evaluation must be thoroughly
familiar with the specific tests/observations. HE/SHE
will decide upon the next actions
Preventive Maintenance
EMA performing
Verification
Ground fault
working at Greer
Industry
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Perform the work!
No good to test and inspect if problems aren’t
resolved
Keep it clean
Keep it dry
Keep it tight
Keep it cool
Preventive Maintenance
EMA Service Engineer, Charles Smith
Performing start up check on a Toshiba
T300MVi at Greer Industry in WV….May 2012
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Record Keeping
Most overlooked part of PM program
The factor in tracking cost savings
Tracking test results over time help identify failures
before they occur
Preventive Maintenance
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Specific Equipment Maintenance Considerations
Preventive Maintenance
EMA of NY Service Manager, Jon
Blasklee Performing Pre-PM check on a
Toshiba T300MVi at United
Water…February 2013
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AC Drive PM ConnectionsCabling
ShieldedPowerMotorCapacitorsCoolingCleaningTuning
Preventive Maintenance
EMA Service Engineer, Charles Smith and Alfaredo
Performing Pre-Start up checks on a Toshiba T300MVi
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Component Failure
Electrolytic Bus
Caps
5 Years
Cooling Fan 3 Years
Contact Relays 500,000 operations
Connectors 100,000 Operations
Per Toshiba Study / Oil filled Caps and Electrolytic
Preventive Maintenance
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Type of Capacitor
• Oil filled and aluminum electrolytic
capacitors used in the Medium
Voltage Drives have specific life
expectancy that will contribute to the
life time cost of the Drive. Oil filled
capacitors have a 20-30 year life
expectancy compared to a 7-9 years
of an electrolytic capacitor.
Replacement of these aluminum
electrolytic capacitors is a very
significant expense and usually
requires at least one week of
downtime.
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Oil filled Caps Vs Electrolytic
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Bus Caps are Usually secured withClampsClamps help prevent swellingBe sure to tighten when replacing capsInspect buss capacitor for leakage and bulging
Preventive Maintenance
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Capacitor Life is affected by:TemperatureOvervoltageMounting/ClampingShelf Life
Preventive Maintenance
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Overvoltage ShortensCapacitor Life
Preventive Maintenance
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Increase in Temperature
Causes increased Electrolytic Loss
Preventive Maintenance
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Overcurrent conditions plusHigh Temperature rapidly accelerates
Capacitor failure
Preventive Maintenance
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Reform Bus capacitors on Spare Cells before
rotating cells…Applies to Voltage Source Drives
Preventive Maintenance
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Therefore… for Cap Life…Keep the Drive CoolCheck your line voltageDon’t overload your DrivesTighten your clamps
Electrolytic Bus capacitors life span
Preventive Maintenance
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Drive Cooling fans are easily checked,
But often overlooked.Apply 480V three phase to the fans
Listen for them running
Rotate them by hand and listen to bearing noise
Feel the air flow
Verify redundant fans are working if applicable
VFD Cooling fans
Preventive Maintenance
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Connections Matter!
Power and Control Wiring in
Separate conduit
Shields properly connected
Grounding connections tight
And properly made
Conduit connections tight
Power and control terminals
Checked for tightness
Preventive Maintenance
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Diodes, IGBTs, the
Power Device of Choice
Use on Voltage Source
Drives
They usually fail by shorting
Check connections
Should be mounted securelyFor cooling
Preventive Maintenance
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Check gate resistance
Check anode/Cathode for low reading
Check for tightness of power and gate leads
Check mounting tightness, which allows for cooling
Current Source Drives use Thyristors
IGCTs, SGCT, SCRs
Preventive Maintenance
Integrated Gate-Commutated Thyristor, Symmetrical Gate Commutated Thyristor and Silicon Control Rectifier
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Dust absorbs moisture resulting in failure
Use compressed dry air….Moisture free
Preventive Maintenance
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Moisture resulting in corrosion on the
board, resulting in damage of traces
Preventive Maintenance
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Other AC Drive PM Considerations
Preventive Maintenance
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Transformer PM
Sound Level Variations
Voltage Levels +/- 5%
Heating
Colorization of windings (dry type)
Liquid Levels (oil filled)
Oil replenishment
Insulation
Connections
Preventive Maintenance
EMA of GA Service Manager, Trey Mayfield Performing Transformer check
on WEG MV01 MV transformer at American Cement 2011
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Transformer PM
Preventive Maintenance
Damaged phase shifting transformer from Siemens Harmony VFD
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Meg the motor
Predictive Maintenance
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SwitchGear, Disconnects and Contactors
Preventive Maintenance
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Switchgear PM
Failures are often
catastrophic
Use qualified people ONLY
Follow Manufacturer’s
procedures and safety rules
Items of concern are
sequencing, Auxillary contacts,
fault current interruption,
connection integrity
Preventive Maintenance
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VFD Power Supplies
Most VFDs including MV VFDs use
DC to DC conversion to produce the
low DC power supplies like 5V, 24V,
12V and -12V.
Power resistors and transformers
around the capacitors can cause
over heating
Preventive Maintenance
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Power On Testing
All Checks Perform in Low Voltage
Compartment
Discoloration on power supplies filtering
capacitors and transformer
Check Switching Power Supplies for
tolerance (24V, 15V, -15V, 5V) and also for
ripples
Check output waveform on the low
voltage compartment with scope and also
input waveform
Check your current feedback on low
voltage compartment
Check the buss ripple
Preventive Maintenance
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Voltage Ripple
Preventive Maintenance
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Preventive Maintenance
Good DC Bus Voltage
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Preventive Maintenance
Switching noise on DC Bus Voltage
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Preventive Maintenance
Snubber board
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Preventive Maintenance
Bad bus capacitors due to switching noise
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Preventive Maintenance
DC Bus Ripple on PQube3
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Programming/TuningVolt/Hz PatternTorque/LimitAccel/Decel
Save your parameters!
Preventive Maintenance
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Shop Repairs on VFDs, Multilins and HMI
Field Service on VFDs and PLCs
Turn Key System Retrofits on VFD/PLCs
PM (Predictive and Preventive Maintenance)
MV VFD, MVSS and Low Voltage VFD sales
Training (Two day VFD hands on training)
EMA Services
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Questions?