VA TECH Transmission & Distribution
1Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
Overcurrent Protection
Fundamentals of Operation and Application
K. Hearfield
VA TECH Transmission & Distribution
2Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
1a) Overcurrent Condition
LoadLoad
Shortcircuit
Current increaseswith load
MOTOR MOTOR
Overcurrent protectionis provided for short
circuit clearance
Overload protection isrelated to therm al
capacity of the plant
Most com m only used overcurrent devices are fuses and relays
OVERCURRENT CONDITION OVERLOAD CONDITION
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3Cc/Hydro_Präs/Interne RS.ppt
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2a) Overcurrent Protection for Phase Faults
3 PhaseO vercurrentRelay
Relays are used in conjunctionw ith circuit breaking device
Fuses
Detect and interrupt overcurrents3 Phase Fault
2 Phase Fault
2 PhaseO vercurrentRelay
Fault m agnitude lim ited byim pedances o f prim ary p lant
Can provide cost saving - w idely used ,but not suitab le for a ll app lications
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4Cc/Hydro_Präs/Interne RS.ppt
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2b) Overcurrent Protection for Earth Faults
2 PH - E Fault
PH - E Fault
3 PH - E Fault
Residuallyconnectedrelay
CoreBalanceCT
Zero outputfor balanced
or phase faultconditions
EF current path thrugenerator earth
Fault m agnitude lim ited by:Prim ary p lant im pedanceM ethod of earthingSystem neutral resistance
Sensitive protection m ay be required- settings below load current
EF current path thrutransform er earth
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5Cc/Hydro_Präs/Interne RS.ppt
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2c) Combined Overcurrent and Earth Fault Protection
2 Phase Overcurrent and Earth Fault 3 Phase Overcurrent and Earth Fault
Can provide cost saving - widely used,but not suitable for all applications
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6Cc/Hydro_Präs/Interne RS.ppt
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3) Methods of System Earthing
SOLID
High EF Current
EARTHINGTRANSFORM ERUsed w here systemneutral not availab le
RESISTANCELow 400 - 1200AHigh 5 - 100A
REACTANCESm aller and lessexpensive than resistance.Can cause high over-vo lts .
PETERSON COILReactance chosen toequal system capacitance
ISOLATED NEUTRAL
Zero EF Current
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7Cc/Hydro_Präs/Interne RS.ppt
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PROTECTION CO-ORDINATION AND GRADING
VA TECH Transmission & Distribution
8Cc/Hydro_Präs/Interne RS.ppt
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4) Radial Distribution System
HVPow erSource
S /S tn A S /S tn D S /S tn ES /S tn CS /S tn B S /S tn F
Selective fault clearance is required forPH ASE-PH ASE and PH ASE-EAR TH faults
Instantaneous overcurrent protection at eachlocation w ould not provide d iscrim ination.
U N N AC C EPTAB LE TO SH U T D OW N W H OLESYSTEM FOR EVER Y FAU LT
R adial Pow er System
Pow er source feeds through a num ber ofsubstations - load taken from each S /Stn
LO A D LO A D LO A D LO A D
M VLoad
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9Cc/Hydro_Präs/Interne RS.ppt
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4.1) Current Graded Protection
2900A2400A
8800A5400A
13100A6850A
BA
Relay at 'A' set tooperate for m ax. faultcurrent at rem ote end
8800A
630A600A1200A
1100A
(EquivalentHV Currents)
M VLoad
Faultcurrent
M ax.M in.
F1
F2
AIM - Protection co-ordinated to ensure m inim um unfaulted load isdisconnected
Unreliable Schem eCurrents F1 and F2 m ay be sim ilar - loss of discrim inationFor m inim um infeed A - B m ay be unprotected
NOTE: M ax. fault at S/Stn. E < m in. fault current between D-E
AD C B
630A8800A
2900A
1200A
F
E
DC
t
Amps
RADIALDIST RIBUT IO N
SYST EM
VA TECH Transmission & Distribution
10Cc/Hydro_Präs/Interne RS.ppt
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4.2) Time Graded Protection
Infeed
BA
1.4s
MVLoad
A
D
C
B
F
E
DC
t
Am ps
1.0s 0.6s 0.2s
0.2s
1.4s
1.0s
0.6s
Operatingcharacteristic:Definite tim edelay
Relays nearer to power source are set tooperate in progressively longer tim es
DISADVANTAGELongest clearance tim e for faults nearestto source
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11Cc/Hydro_Präs/Interne RS.ppt
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Inverse Definite Minimum Time (IDMT) Operating CharacteristicOperate current = 1.05 x setting
At 2x setting operate time = 10s
At 10x setting operate time = 3s3/10 operating curve
At 30x setting operate time = 2sDefinite minimum time
Numeric IDMT relay operating algorithm:
2s
3s
10s
2x 10x 30x
T ime M ultip lie r = 1.0
Op
era
tin
g T
ime
M u ltip le o f Current Setting
..
1
14.002.0 MT
II
t
S
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12Cc/Hydro_Präs/Interne RS.ppt
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Current and Time Grading of IDMT Curves
2s
3s
10s
2A 10A 30A
0.2s
0.3s
1s
2A 10A 30A
Current Setting 1AT ime M ultip lie r 1 .0
Current Setting 1AT ime M ultip lie r 1 .5T ime M ultip lie r 0 .1
2.27s
3.62s
24.5s
2A 10A 30A
Current Setting 1.5AT ime M ultip lie r 1 .0
15s
4.5s
3s
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13Cc/Hydro_Präs/Interne RS.ppt
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0 .1
1
10
100
1000
10000
Time(sec)
Long Time Inverse
Normal Inverse
Current (m ultiples of setting)
1 10 1002 3 4 5 6 8 20 30 50 70
Extremely Inverse
Very Inverse
IDMT Curve - General applications
..
1
14.002.0
MT
I
It
S
VIDMT CurveCloser grading where faultlevels differ significantly
..
1
5.13MT
I
It
S
EIDMT Curve – Grading with fuses
..
1
802
MT
I
It
S
LTIDMT Curve - Grading with liquid resistor
..
1
120MT
I
It
S
Characteristics can be supplemented with LS and HSStages e.g. to assist grading with complex characteristics
4.3a) IDMTL Curves - Time and Current Grading
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14Cc/Hydro_Präs/Interne RS.ppt
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4.3b) Fuse Co-ordination
RequiredT ime
Delay"G rading
M arg in"
M in imumRelay
O peratingT ime
Pre-Arcing
Arcing
RelayO vershoot
0 m s Pre-Arcing
Arcing
SafetyM arg in
0 m s
Pre-Arcing
Betweenrelayandfuse
Betweentwo
fuses
Recom m ended current ratio 3:1- avoids overlap of characteristics
Recom m ended current ratio > 2:1
t' = 0.4tf + 0.15s
T.D. of 0.2s will ensuregrading at high fault levels
EIDM T relay &fuse characteristics
Fusecharacteristics
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15Cc/Hydro_Präs/Interne RS.ppt
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4.3c) Co-ordination between Time Graded Relays
RequiredTim e
Delay"G rading
M argin"
M inim umRelay
O peratingTim e
M axim umRelayO peratingTim e
CT Error- IDM T only
CircuitBreakerTrippingTim e
O v ershoot(R2)
SafetyM argin
0 m s
RequiredTim e
Delay"G rading
M argin"
M inim umRelay
O peratingTim e
Pre-Arcing
Arcing
O v ershoot
0 m s
Betw eenrelay and
fuse
Betw eentw o
relays
Recommended current ratio 3 :1
R1R2
VA TECH Transmission & Distribution
16Cc/Hydro_Präs/Interne RS.ppt
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4.3d) Time Grading - Nominating Grading Margin
CB T rip T im e 150m s 80m s
Safety Marg in 50m s 40m s
O ver-shoot 80m s 40m s
T im ing Error 7.5% 5%
Argus2T JM
O lderSystem
New erSystem
CT Error
CircuitBreakerTrippingTim e
Overshoot
SafetyMargin
0 m s
Max. Op. T im e
RequiredTim e
Delay"Grading
Margin"
M in. Op.Tim e
250ms
CT Error
CircuitBreakerTrippingTim e
Overshoot
SafetyMargin
0 m s
Max. Op. T im e
RequiredTim e
Delay"Grading
Margin"
M in. Op.Tim e
400ms
Older System
Newer System
VA TECH Transmission & Distribution
17Cc/Hydro_Präs/Interne RS.ppt
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4.3e) System Study for IDMT Protection
Infeed
BA
F
EDC
300/5
50A165A 95A 80A
33/11kV10 MVA
33kV Bus 11kV Bus
390A400/5 225A 200/5 100/5
11kV/415V1 MVA
X = 7%
X = 4%1600A
130A
3ph Max. Fault3ph. M in. Fault
12596A6846A
5753A4156A
2882A2417A
1410A1289A
626A601A
Current Setting - Higher than m ax. load
Tim e graded @ m ax. 3ph. fault current
PROCEDURE
Grade: D with FuseC with DB with CA with B
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18Cc/Hydro_Präs/Interne RS.ppt
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4.3f) IDMT Grading Calculation Results
Infeed
BA
F
EDC
300/5
50A
165A 95A 80A
33/11kV10 M VA
33kV Bus 11kV Bus
390A400/5 225A 200/5 100/5
11kV/415V1 M VA
X =7%
X =4%
1600A
130A
3ph M ax. Fault 12596 5753A 2882A 1410A 626A
@ D: P.S.M . = 626/(100 x 1.25) = 5For p .s.m . 5: N I operating tim e = 4.3s4.3 x T M S = 4.3 x 0 .05 = 0.215s
G rad ing m arg in steps 0.4s
Relay at 'A ' operates for a close up fault in 0.75s.IDM T fault c learance tim e < DT L tim e
DT L system relay at 'A ' operate tim e = 0.2 + 3 x 0.4 = 1.4s
t
Amps
A
D
CB
5753626
28821410
0.205
1.050.630.54
RelayCurrentSetting
T M S
A 125% 0.375
D 125% 0.05
C 75% 0.175
B 100% 0.275
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19Cc/Hydro_Präs/Interne RS.ppt
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Power and Voltage Ratings
Equipment Impedances
CT Ratios
Fuse Ratings
Relay Characteristics
4.4a) Industrial System Protection Co-ordination Study
Single Line Diagram
11/0.4 kV1500 kVA
5%
280 M VA
2500/12500/1
1600/1
450A
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20Cc/Hydro_Präs/Interne RS.ppt
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4.4b) Co-ordination Issues
Single LineDiagram
Norm al OperationEm ergencyOperation
No OperatingRestrictions
25kA
25kAF
25kA
25kA
44kA
22kA
Establish load flow and short circuit currents
Grading curves plotted beginning at low est voltage level and largest load.
Grade at the m axim um fault level that can be seen by both relays sim ultaneously.
Grade at fuse cut-off point if less than the above.
F F
1000A
500A
2000A
500A
1000A
500A
VA TECH Transmission & Distribution
21Cc/Hydro_Präs/Interne RS.ppt
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Protection Grading - Software
VA TECH Transmission & Distribution
22Cc/Hydro_Präs/Interne RS.ppt
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PROTECTION FOR LOW EARTH FAULT CURRENT LEVELS
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23Cc/Hydro_Präs/Interne RS.ppt
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5.1) Sensitive Earth Fault Protection
CoreBalanceCT
Core sum m ates fluxes o f prim ary currents
O nly one core is used - CT m agnetis ing currentis reduced by approxim ately 3 to 1
Num ber o f secondary turns need not be relatedto rated current o f protected circuit - can beoptim ised to protection setting
SEF relay current setting as low as possib lelim ited by residual unbalance capacitance -estab lished by test
Low CT burden required - e .g . num eric re lay
DT L characteristic , back-up function
S.E.F . Relay
Low earth fau lt current
Sem i insulating ob ject
VA TECH Transmission & Distribution
24Cc/Hydro_Präs/Interne RS.ppt
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5.2) Neutral Displacement ProtectionBalancedSystem
voltages
V RES = 0
R phase EF
V RES= V YR + V BR= 3V PH
EF on non-effectively earthed system
Faulted phase m ust not rem ain energised.
EF current very sm all- OC detection m ay be im practical
NDR detects residual voltage to earth
Operation not discrim inative- tim e delay required
NDR
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25Cc/Hydro_Präs/Interne RS.ppt
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HIGH-SET INSTANTANEOUS PROTECTION
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26Cc/Hydro_Präs/Interne RS.ppt
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6a) High Set Overcurrent Protection
Reach of h igh set700012500
A B
5700
Inverse time e lement
Inverse time e lement
Inversetime e lement
Reach of h igh set
Set above max. fau ltcurrent a t s/stn. B
Instantaneous h igh-setprimary setting 7000A Plain Feeder
Transform er Feeder
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27Cc/Hydro_Präs/Interne RS.ppt
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6b) HSOC Example - Calculating System Impedances
Inverse tim e elem ent
Transformer Feeder33kVM ax fault 1000 M VAM in fault 650 M VA
20km (0.3 + j0 .43) O hm s/km
Instantaneous high-set
33/11kV24M VAZ = 22.5% 11kv
To determine system impedances:
OHL impedance = 20(0.3 + j0.43) = 6 + j8.6 Ohms
Source impedance M in = j330002/1000 x 106 = j1.09 OhmsM ax = j330002/650 x 106 = j1.68 Ohms
Transformer 100% impedance @ 33kV = j330002/24 x 106
= j45.38 Ohms22.5% impedance on 24M VA = 0.225 x 45.38
= j10.21 Ohms
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28Cc/Hydro_Präs/Interne RS.ppt
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6c) HSOC Example - Establishing Relay Setting
IDM T elem ent
33kV SourceM ax im pedance = j1 .68 O hm sM in im pedance = j1 .09 O hm s 6 + j8 .6 O hm s
HSO C
33/11kVj10.21 O hm s 11kV
3ph m ax infeed917A @ 33kV
M in infeed:3ph fault 1601Aph-ph fault 1387A
W here com prom ise is necessary: Stability is preferred to high speed protection
M in. system im pedance to LV busbars = m in source + line + transform er= j1.09 +(6 + j8.6) + j10.21 = 20.78 Ohm s
M ax. LV 3-phase fault = 33000/(1.732 x 20.78) = 917A
M ax. system Z to transf. HV side = m ax source + line= j1.68 +(6 + j8.6) = 11.9 Ohm s
M in. HV 3-phase fault = 33000/(1.732 x 11.9) = 1601A
M in. HV PH-PH Fault = 0.866 x 1601 = 1387A
Best achievable grading m argin = (1387/917)^0.5 = 23%i.e. RELAY SETTING OF APPROX 1128A PRIM ARY
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29Cc/Hydro_Präs/Interne RS.ppt
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APPLICATION OF OVERCURRENT PROTECTION
SPECIAL CONSIDERATIONS
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30Cc/Hydro_Präs/Interne RS.ppt
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7.1a) Effect of System Capacitance in Resistance Earthed System
Instantaneous earth fault protection can be used to protectfeeder and un-earthed transform er w inding, how ever:
For an earth fault at F1:EF relay on healthy circuit m ay operate if not set above ICIC = IB C + IYC = 3 x nom inal charging current/phase
F1 D elta or U n -Earthed S tarW inding
IBC
IYC
IC
V R
IYC
IBC
IC
V YV B
N
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31Cc/Hydro_Präs/Interne RS.ppt
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7.1b) EF Protection Applied to Non-Earthed Transformer Feeder
F1
IBC
IYC
IC
7km FeederCharging current - 1.8A/km
33kV
V R
IYC = 21.8A
IBC
IC = 37.8A
V YV B
N
On occurence of an EF (F1) the affected phase w ill be earthed. 33kVsystem is resistance earthed, healthy phase voltage rises to linevolts level.
Normal per phase capacitance increased by a factor of 1.732
For fault F1:EF relay on healthy circuit may operate if not set above I CIC = 7 x 1.8 x 3 = 37.8A primary
Set relay 2 to 3 x 37.8A i.e. 75 - 112.5A
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32Cc/Hydro_Präs/Interne RS.ppt
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7.2) HSOC & EF Protection for Transformer Feeders
F2
F1F3
TRIP
E 1
P
E 2
P = Phase fault protection relayE 1 = Residual earth fault relayE 2 = Earth fault check relay
Earthed W inding
Provides inst. prot for transform er feeder phase and earth faults
For fault F3 E2 w ill not operateFor fault F2 E1 w ill not operate
P Set to> 1.5 x m ax. lv fault current> 2 x m in. in zone (hv) fault current
E 2 Set to< P (for faults at F2 E 2 m ay operate but P m ust not)> LV infeed to a fault at F3 (s ince E2 operated by +ve and -ve sequence currents)
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7.3) Faults on Star Delta Transformers
KI
3
KI
3
SO URCE
F
KI
3
KI
3
F
KI
3
SO URCE
I
II
I
I
I
K
I
3
2
Earth faults on star side of transformer is seen as a phase fault on Delta side
A phase fault on the star side of the transformer requires an additional current grading margin of :
Care must be taken if applying 2 phase overcurrent protection to HV side:2P protection suitable if minimum fault current/full load current > 4
%163
2 I
I
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34Cc/Hydro_Präs/Interne RS.ppt
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7.4) - Two Stage Overcurrent Protection
IDM T
Stage1 T rip
DT LStage2 T rip
SeparateHV and LVO vercurrentProtection
2 Stage OvercurrentProtection
Im proved discrim inationReduced grading m argin
CT and Relay cost saving
Not applicable if there is apossibilty of LV infeed totransform er faults
IDM T
IDM T
HV Source HV Source
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35Cc/Hydro_Präs/Interne RS.ppt
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7.5) - Interlocked Overcurrent Protection
Interlocked Overcurrent Relay
Normally Inhibited - UntilOperation of Busbar Prot.
Unit Feeder Protection
BusbarProtection
F1
F3
F2
Feeder
F1 - Cleared by busbar protection
F3 - Cleared by circuit protection
F2 - Operates busbar protectionW ill not be cleared by fdr. prot.
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36Cc/Hydro_Präs/Interne RS.ppt
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7.6) Voltage Dependent Overcurrent Protection
Volts Contro lled O C
Inhib its overcurrent pro tection unlessvoltage is below set-po int:T ypically 0.7 - 0 .9 V n
NET W O RK
O vercurrent relay m ust be graded w ith netw ork protection
Close up generator faults - initia lly high current.M ay reduce rap id ly - lim ited by am plitude of exitationcurrent and d irect axis synchronous reactance
Volts Restrained O C Characteristic
Tap
Settin
g as %
of T
apS
etting
at Rated
Vo
ltage
25 1007550
25
50
75
100
Input Voltage (% of rated vo ltage)
G enerator
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37Cc/Hydro_Präs/Interne RS.ppt
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7.7) Flashing Fault ConditionFAULTClashing conductors or re-sealing cab leR1R2
Loss of grading /discrim ination m ay occur:
If R2 Electrom echanical & R1 Inst. reset or if R2 DTL reset and R1 electrom echanical
Som e com prom ise m ay be necessary where m ore than two relay points are in series
R3D
isc
Tra
vel
E lectro -m echanical Relay
T im e
T RIP
% o
f A
lgo
rith
m
Argus (Inst. Reset)
T im e
Argus (DT L Reset)
T R IP
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38Cc/Hydro_Präs/Interne RS.ppt
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DIRECTIONAL PROTECTION
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39Cc/Hydro_Präs/Interne RS.ppt
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8a) Parallel Feeders - Application of OC Protection
LO AD51 51
5151
A
B
C
D
LO AD
51 51
5151
A
B
C
D
I1
I2
Faulted feeder:Fault current can flow in both d irectionsRelays C and D operate togetherBoth feeders w ill be tripped
I1 + I2
Conventional grad ing:G rade A w ith CG rade B w ith DA and B have the sam e settingC and D have the sam e setting
A & B
C & D
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8b) Parallel Feeders - Directional Protection
Solution to faulted feeder prob lem :D irectional contro l o f Relays C and DRelay D on unfaulted feeder does not operate
SET T ING PHILO SO PHY :
Load current alw ays flow s in non-operate d irection
Any current flow ing in operate d irection is ind icativeof a fault condition.
T herefore relays C and D m ay have sensitive setting ,fast operating tim e
C & D usually set to 50% full load , low T .M .S (0.1)
LO AD
67
6751 B
C
D
I1
I2
I1 + I2
51 A
51 E
G RADING PRO CEDURE
G rade A and B w ith E , assum ing onefeeder in service
G rade A w ith D (and B w ith C )assum ing both feeders in service
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9a) Ring System - Application of Time Graded OC Protection
LO AD
RM U
LO AD
RM U
67 67
LO AD
RM U
67 6751
LO AD
RM U
67 67
LO AD
RM U
67 6751 67
SourceSubstation
67
W ith ring closed both load and fault current may flow in either direction - directional relays are required
Directional relays look into feeders - aw ay from busbars
Non-directional relays can be used: At the source substationOn the RM U circuit w ith the longer time delay
A
F E D
CB
A'
B ' C ' D '
E 'F '
0.9
2.1 0.1 1.7 0.5 1.3 0.9
1.30.51.70.12.1
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42Cc/Hydro_Präs/Interne RS.ppt
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9b) Grading of IDMT Relays in Ring Main SystemRM U
LO AD
RM U
67 67
LO AD
RM U
67 6751
RM U
67 67
RM U
67 6751 67
SourceSubstation
67
A
F E D
CB
A'
B ' C ' D '
E 'F '
Grading Procedure for IDM T Relays
Grading margins established at highest current level seen byboth relays
Highest fault level occurs w ith ring closedHighest branch current occurs w ith ring open
Open ring at AGrade A' - F' - E' - D' - C' - B'
Open ring at A'Grade A - B - C - D - E - F
Relays A, B, C, A', E', F' may be non-directional
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9c) Grading of Ring Main with Argus Numerical Relays
LO AD
RM U
RM U RM U
51
RM U RM U
51
SourceSubstation
Directional (Argus2) num erical relays can be set to tri-state, allowingtotally independent forward and reverse settings to be applied.
Outputs of Argus configured to trip relevant circuit breaker
Cost saving - less relays, CTs, installation etc.
67 67 67
6767
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9d) Problem of Grading Ring Main with Two Sources
Correct discrimination betw een directional overcurrent relays is not possible:
For F1 - B' must operate before A', A before D
For F2 - B' must operate after A', A after D
67 6767
A BB'
SourceSubstation
67
C'
67
A'
67
C
F1
F2
RMU
67 67
D D'
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45Cc/Hydro_Präs/Interne RS.ppt
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9e) Grading Ring Main with Two Sources
67 6767
A BB'
Source 1Substation
67
C'
50
O ption 1T rip least im portantsource instantaneouslyT hen treat as ring m ainw ith sing le source
RMU
67 6767
A'
67
CD D'
8787
Source 2Substation
O ption 2F it p ilo t w ire protection tocircuit A - BConsider S/Stns A & B ascom m on source busbar
VA TECH Transmission & Distribution
46Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
10a) Establishing Current Direction for Phase Faults
Directional O C protection required if current can flow in both d irections through relay location e.g .Paralle l feeders, R ing m ain circuits
D irection of a .c. is by inference not an absolute quantity, it is m easured relative to som e reference quantity alternating atthe sam e frequency - the system vo ltage.
I = O PERAT ING Q UANT IT YReference V = PO LARISING Q UANT IT Y
Com paring phase current (e .g . IRED) w ith relevant phase vo ltage (e.g . V RED) w ould ind icate d irn o f current flow , how ever;
P.F . USUALLY LO W (Pow er system apart from loads is reactive)
USE O F FAULT VO LT AG E IS UNRELIABLE (System volts at po int o f fault w ill co llapse tow ards zero)
Each phase of d irectional overcurrent relays m ust be polarised w ith a vo ltage w hich w ill not be reduced excessively (c loseup 3-phase faults notw ithstanding)
VA TECH Transmission & Distribution
47Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
10b) Table Illustrating Relay Connections
E xam ple – R ed P h ase
V R
V YVB
V R -B
IR300
V R
VYV B
VR -B
IR -
Y 600
V R
V YV B
-VB -NIR
600
VR
V YVB
VY -B
IR
RedPhase
YellowPhase
BluePhase
APPLIEDCURRENT
APPLIEDVOLTAGE
APPLIEDCURRENT
APPLIEDVOLTAGE
APPLIEDCURRENT
APPLIEDVOLTAGE
APPLIEDCURRENT
APPLIEDVOLTAGE
300 Connection600 No .2 Connection
Risk o f m al-operationfor all fault types
600 No .1 ConnectionRequires deltaconnected CT s
900 Connection
V B-Y
V Y-R
V R-B IR-Y
V B-Y
V Y-R
V R-B
IB-R
IY-B
-V Y-N
-V R-N
-V B-N
V R-Y
V B-R
V Y-B
E xam ple – R ed P h aseE xam ple – R ed P h aseE xam ple – R ed P h ase
IR
IB
IY
IR
IB
IY
IR
IB
IY
VA TECH Transmission & Distribution
48Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
10c) 900 Relay Connection with Selectable MTA
For balanced system conditions:90 - 30 RelayM TA: Primary system volts leads primary system current by 600
Zero torque limits: Primary system volts leads primary system current by 1500
Primary system volts lags primary system current by 300
90 - 45 RelayM TA: Primary system volts leads primary system current by 450 W .K Sonnemann:Zero torque limits: Primary system volts leads primary system current by 1350 This relay gives the best characteristic
Primary system volts lags primary system current by 450 to fit the spread of possible phase angles
IT zero
IU PF
V
Im axT
IT zero
-450
1350
450
90 - 45 RelayBalancedprimarysystemconditions
RelayPhase
AppliedCurrent
AppliedVoltage
M TA(I w rt V)
Relay Circuit
R IR VY-B
30
B IB VR-Y
Y IY VB-R
R IR VY-B
45
B IB VR-Y
Y IY VB-R
I
I'
MTA
V300
I
I'
MTA
V450
M TA = d isplacem ent ofcurrent and voltageapplied to relay
VA TECH Transmission & Distribution
49Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
11a) Establishing Current Direction for Earth Faults
Require:O PERAT ING Q UANT IT Y, PO LARISING Q UANT IT Y
O perating SignalO btained from residual connection o f line CT s IOP = 3 Io
Polaris ing SignalP h - P h o r P h - E vo ltag es used in o vercurrent p ro tec tio n
becom e inappropriate.Residual vo ltage is used as the po laris ing quantity
VA TECH Transmission & Distribution
50Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
11b) DEF - Extracting Residual Voltage
To allow for the flow of zerosequence voltage com ponents:
VT prim ary m ust be earthedVT can be of 3 phase, 5 lim b construction or3 single phase units
VRES
VRES = VA-G + VB-G + VC - G = 3VO
O pen delta VTsecondary
VA TECH Transmission & Distribution
51Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
11c) DEF - Residual Voltage for Solidly Earthed Systems
Z S/Z L high
Z S/Z L low
SystemVolts
SystemVolts
ResidualVo lts
ResidualVo lts
S Z S R Z L F
V R
V R
V R
V R
M ay lim ituse o f vo ltage
polarised relays- m odern relaysvery sensitive
Sourceim pedance
Lineim pedance
V R =ResidualVo ltage
CHECK FO R SUFFIC IENT PO LARISING VO LT AG E!
VA TECH Transmission & Distribution
52Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
11d) DEF - Residual Volts for Non-Effectively Earthed Systems
ResistanceEarthed
SystemVolts
SystemVolts
ResidualVolts
ResidualVolts
S
ZS
R
Z
L
F
Insulated orPeterson
CoilEarthed
SR
SR
VR VR
VR(may
approach3VPH)
VR VRVR
SUFFICIENTPOLARISINGVOLTAGE SHOULDALW AYS BEAVAILABLE
Volts dropdue to earthresistance Neutral point
raised aboveearth potential
Neutralfullydisplaced
VA TECH Transmission & Distribution
53Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
11.2) DEF - Relay Connection with Selectable MTA
M TA (I wrt V)
O 0 -150 -900-650-450
Resistive Neutral Reactive Neutral
V RES
VRES
IRES
VRES
IRES
VRES/IRES = 00 VRES/IRES = 900
V RES
IRESIRES
IRES
IRES
IRES
V RESV RESV RES
ResistanceEarthedSystem s Distribution System
- Solid ly EarthedT ransm ission System- Solid ly Earthed
ReactanceEarthedSystem s
Earthing T ransform erw ith Resistor
VA TECH Transmission & Distribution
54Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
11.3a) Polarising with Neutral Current
Polarisingsignal
VOLTAGE POLAR IS IN G M AY N OT B E PR AC TIC AB LE
i) A solid ly earthed, h igh fault level (low source im pedance) systemm ay result in a sm all value of residual voltage at the relaying point.
ii) VTs m ay not be available
iii) VTs m ay not be suitable - no zero sequence path
If a reliable polarising signal is not available then the relay m ay bepolarised from a suitable current source:e.g . from a C T located in a suitable system neutral to earth .
For relay operation:Polarising and operating current should be in phase
N eutral current of a pow er or earth ing transform er m ay be used- but only if earth fault neutral current alw ays flow s tow ards the systemN eutral of S tar/D elta w ill alw ays flow in correct d irection for polarisingD ouble earthed Star/S tar and Auto-transform ers require study.
A
B
VA TECH Transmission & Distribution
55Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
11.3b) Current Polarising from 2 Winding Transformers
P OL OP
DEF Relay
INC O RRECT
P OL OP
DEF Relay
CO R REC T
P OL OP
DEF Relay
CO R REC T
P OL OP
DEF Relay
INC O RRECT
VA TECH Transmission & Distribution
56Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
11.3c) Current Polarising from 3 Winding Transformers
P O L O P
DEF RelayCORRECTif ZLO + ZSO is positive
SOURCE
H L
UnloadedDelta
LoadedDelta
Relaypolaris ingcircuit
Relaypolaris ingcircuit
VA TECH Transmission & Distribution
57Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
11.3d) Current Polarising of DEF Protection on Auto-Transformer Circuit
N e u t r a l c o n n e c t i o n i s s u i t a b l e f o r c u r r e n t p o l a r i s i n gi f e a r t h f a u l t c u r r e n t f l o w s ' u p ' t h e n e u t r a l f o r f a u l t so n H V s i d e
F o r c o r r e c t a p p l i c a t i o n , c h e c k :
1 L
H
TOLOSO
TO
V
V
ZZZ
Z
W h e r e :Z T O = T e r t i a r y w i n d i n g z e r o s e q u e n c e i m p e d a n c eZ L O = L V w i n d i n g z e r o s e q u e n c e i m p e d a n c eZ H O = H V w i n d i n g z e r o s e q u e n c e i m p e d a n c e
( N o t e t h e r e i s a l s o a p o s s i b i l i t y t h a tn e u t r a l c u r r e n t m a y b e z e r o )
SO URCE
PO L O P
DEF Relay
Z H Z L
Z T
Current polarising fromtransformer delta preferred
(if transf. has delta w inding)
VA TECH Transmission & Distribution
58Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
12) Application Consideration - 2 out of 3 Tripping
D irectional R elay C onnected in to H ealthy C ircuitFW D . = d irection of load
3450
2250
1650
1050
450
2850
B REV
C FW D
A REV
IB=IC=+1
IA =-2
HV Infeed
R - BFault
LV DOCRelays
For H V ph-ph fault one phase of relay m ay incorrectlyoperate in FW D dirn - depends on phase angle of fault.
Select 2-out-of-3 logic, then a m inim um of tw o phasesm ust be in itiated for a trip output to be issued
REV
VA TECH Transmission & Distribution
59Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
OVERCURRENT RELAYS
VA TECH Transmission & Distribution
60Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
13.1) - Electromechanical Induction Disc Relay - Reyrolle Type 2TJM
TO RQ UE
Upper electrom agnet
Low erelectrom agnet
Prim aryw inding
Plug bridge
Secondaryw inding
Disc
Electromagnetic system operates on a movable conductor– aluminium disc, on which a contact assembly is mounted
Torque is produced by interaction of two alternatingmagnetic fields mutually displaced in space and time
T = K. 1. 2.sin
Where:T = Torque
1 = Flux 1 i.e. flux produced by upper electromagnet
2 = Flux 2 i.e. flux produced by lower electromagnet
Single function device1 Current input2 o/p contactsFlag indicator
VA TECH Transmission & Distribution
61Cc/Hydro_Präs/Interne RS.ppt
PEEBLES REYROLLE
13.2) Schematic Diagram of Numeric Relay - Reyrolle Type Argus
I> ISLowSet
HS1 HS2A
D
rm s
dc
DTL DTL DTL
Program m ableinterconnection
logic
Statusinput
O UTPUTS
DataCom m s
HM I
1 Phase of relay shown
Multifunction deviceUp to 4 Current inputsUp to 11 o/p contactsLED indicators
StartTrip
8 settings groupsUp to 9 status inputsLCDData storageData comms PC software
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