Post on 26-Mar-2015
© Siemens AG 2006
Distance Protection: Earth-Faults and Fault Resistance Power Transmission and Distribution
Page 2 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Distance protection: Earth fault in system with solid, isolated or compensated system neutral earthing
G
BA C
D
Z1
Z2...
D
ZT
Neutral Earthing :
Peterson Coil or Isolated or Solid
During single phase earth fault:
The short circuit current magnitude depends on the neutral earthing method.
Page 3 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Earth Fault Current - Pick-Up Characteristic
Measuring errors and non-symmetry may not cause incorrect pick-up by earth fault current threshold
Page 4 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Earth Fault Detection Logic
Normal pick-up: 3I0
Heavy load on long line: 3I2
For very small earth current: 3U0 (isolated or compensated system)
Page 5 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Earth fault detection during one pole open condition
During the 1 pole open condition, load current flows in the earth path.
Magnitude comparison of the remaining 2 phases prevents incorrect pick-up
Page 6 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Phase-to-Earth loop:
Phase-to-Phase loop:
Distance measurement Fault loop formulas
2121 LLLLLL IIjXRV
RL + j XLIL1
RE + j XE
VL1 VL2 VL3
IL2
IL3
IE
Relay location
Line and earth impedance are measured
Only the Line impedance is measured
EL
ELLE
L
ELLL
EELLEELLL
EEELLLL
IX
XIjXI
R
RIRV
XIXIjRIRIV
jXRIjXRIV
111
111
11
)()(
Page 7 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Numeric impedance calculation, ph-ph-loop
Infeed
L1
L2
L3
E
Rfwd Xfwd(Lfwd)
Rret Xret(Lret)to remote line end
fwd
ret
Ufwd Uret
relaylocation
faultlocation
U U = X
L3L2
L3L2mL3-L2
-
-
III
L3L2
L3L2L3-L2
-
- e=
II
U UR R
L3L2
L3L2L3-L2
-
II -
U U = Z
With the measurement of phase to phase voltages and currents the fault impedance (impedance to fault location) is correct calculated
Page 8 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
EEL
EPh
L II
k
UZ
Uph-E
G
RL XLL1
L
L2
L3
RE XE
E = (L1 + L2 + L3)
L
E
L
L0L
E 3 Z
Z
Z
ZZk
Numeric impedance-calculation, Ph-E-loop (1)
EL
ELLEEL LEPh I
Z
ZIZZIZI U
Calculation of the complex impedance
Residual compensation factor
Page 9 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Uph-E
G
RL XLL1
L
L2
L3
RE XE
E = (L1 + L2 + L3)
Numeric impedance-calculation, Ph-E-loop (2)
Separate calculation of the resistance and reactance
Separate residual compensation factors
EL
ELLE
L
ELLL
EEELLLL
IX
XIjXI
R
RIRV
jXRIjXRIV
111
11
L
E
E, R R
Rk
L
E
E, X X
Xk
This solution is the preferredin Siemens Relays
Page 10 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Distance measurement (Ph-E-loop) influence of fault resistance
UPh-E
XL
L RL
RF
XE
E RE
K
X
R
X
ZL ZPh-E
RF
1+kE
E-L assume LFELLE-Ph IIII R + Z + Z = U
E
F
E
L
E
LEEL
E-PhE-Ph
+ 1 +
+ 1
+ 1 =
k
R
kZZ
Zk
UZ
II
)-Ej(
L
E
FL
L
E
FLE-Ph
L
EE
Le1
R
1
R then , to adapted setting If
ZZ
Z
ZZ
ZZZ
Zk
Also an additional measuring error in the X-direction
This method is not used by SIEMENS
Page 11 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Distance measurement (Ph-E-loop) - influence of fault resistance at separate residual compensation factors
UPh-E
XL
L RL
RF
XE
E RE
K
X
R
ZL
ZPh-E
RF
1+kE,R
LFEEELLLE-Ph III R +X j + R - X j + R = U
with IE = - IL
RE
FL
L
E
L
EPh
Ph-E + k
RR
RR
+
I
U
R,11
Re
L
L
E
L
EPh
Ph-E X
XX
+
IU
X
1
Im
No measuring errorin the X-direction
Page 12 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Short-circuit with fault resistance and infeed from both sides - equivalent circuit
D
ZLB
UA
EA
RF
A
B
EBA
X
ZL
A
B RF
RF
R
FBALA R + + Z = U A III
FBFLAA R + R + Z = U II
FA
BFL
A
AA R + R + Z =
U = Z
I
I
I
The fault resistor RF is seen larger
Page 13 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Fault locating: distance-to-fault measurement with arc compensation
ISCUSCRF
ZL
RF
ZL
ISCR
X
ZSC
(USC)
SC
ZSC sin SC
XSC= K sin SC = ZSC ·sin SC
USC
ISC
lF
Measurement of the Reactance gives the bestaccuracy
Page 14 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
= I1+I2 - I1
ZL1
XR
UARC/ISC1
1 + k0
for : I1 = IE1 = ISC1 and k0 = =
ZLE
ZL
ZL0 - ZL
3 ZL
ZRel = ZL1 +UARC
(1 + k0) · ISC1
Short-circuit with arc resistance and double-sided in-feed,
influence on distance measurement
U1
IE1
I1ZL1 ZL2
I2
IE2ZE1ZE2
UARC
U1 = I1 · ZL1 + IE1 · ZE1 + UARC
I1 + k0 · IE1
ZRel = = +U1
I1 + k0 · IE1
I1 · ZL1 + IE1 · ZE1
I1 + k0 · IE1
UARC
The phase angle difference between the two sources (load influence) causes an additional error in the measured reactance (see angle )
Page 15 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Influence of load flow on the distance measurement for faults with fault resistance
ZL1 ZL2
U1 U2RF
load
RF = fault resistance
U1U2
1
2
SC1
SC2
L
1
2
X
R
2
1
RF
ZL1
ZSC1
SC1
ZSC1 sinSC1
RF X
R
RF
ZL2
ZSC2
SC2
ZSC2 sin
SC2
1
2
RF
ZK1 = ZL1 + RF + RF
2
1
ZK2 = ZL1 + RF + RF
1
2
An Over-reach(left) or an Under -reach (right) is possible.The grading characteristic mustbe adapted.
Page 16 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Estimation of arc resistance
X Variable R/X-setting
R
Worrington formula:
Ohm ml
AI
28700 R
1,4ARC
Rough estimation: UARC = 2500 V/m
Ohm AI
md V/m 2500 ARCR
F
Phase-to-phase distancesd = 3,5 m (110 kV)d = 7 m (220 kV)d = 11 m (380 kV)
Insulator lengths (long-rod insulator)
l= 1x1,3 = 1,3 m (110 kVl= 2x1,3 = 2,6 m (220 kV)l= 3x1,3 = 3,9 m (380 kV)
Page 17 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Ph-PH-E short-circuit with fault resistances,
Measured loop impedances depending on fault location
RTower
L = 0
100 km12.5 GVA 12.5 GVA
L2-L3-E
4
D1 1
L3-E
L2-L3
L2-E
R
X
50 %
100 %
In the case of multiple earth-faults with fault resistances, complex conditions arise for the distance measurement.
A special logic for loop selection is required (blocking of leading phase (L2-E) to prevent an over-reach)
Page 18 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Loop impedances during Ph-Ph-E short-circuit,
depending on fault resistance to earth and load conditions
RE
RPh = 0
D
Ph-Ph-E
10 GVAloadX0
X1= 1
10 GVAX0
X1
= 1
500 kV; l =310 km
25 10 20
40
2
515
10
20
30
400
100
150
200
50742 MW
-742 MW
RE
RE (Ohm)
50 100
X (Ohm)
X (Ohm)
-742 MW
742 MW
laggingphase
leadingphase
The impedance of the leading phase is seen to be too short.Phase-Phase loop isnearly measured correctly(small X-error)
Page 19 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Effective arc resistance „seen“ by the distance relay with double-sided in-feed (example)
ARCLA A U + Z I = U
A
ARCL
A
AA
II
U + Z =
U = Z
iARC
uARC
D RARC6 m
A = 1 kA B
2 4 6 8 10 BkA
RARC
5
10
15with constantarc voltageUARC = 2500 V/m
with current dependentarc voltage
RLB = Ohm/m28 700
ARC1.4
ARC in A
The rate of arc resistance reducing is greater, if the current increasing is considered
Page 20 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Resultant fault resistance on overhead lines with earth-wire
R R R R R R R R R
earthing resistanceof the station
IPh
IE''
IE'
tower footing resistances
earth-wire(s)
phase-conductors
50 10000
1
2
3
4
5
avarage towerfooting resistance
resultant fault resistance Ph-E
60 mm2 steel wire
2 earth-wires, total 60mm2
tower currents
RLNW RTF RLNW
E
On lines with earth-wires the current flows via several parallel tower footing to earth. The resultant phase-earth resistance which is actually effective, is substantially reduced.
Page 21 TLQ 2004 Distance Protection – Earth Faults and fault resistance
© Siemens AG 2006Power Transmission and Distribution
Quadrilateral characteristic with load cut-out for high line loadability
• High reach for remote back-up and adapted arc tolerance (good fault-load discrimination)
• High arc compensation even with short lines
X
R
RF
X- and R-reach separately settable at all zones
2
1
X
R
RFRF
load
D
RF 1 + 2
1
2
ZF = ZL + RF + RF
2
1
Quadrilateral characteristic is a good solutionfor adapting on high fault resistances.It provide a substantially better resistance coverageand arc compensation than circular characteristic.