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7/31/2019 01_Dist_Part_1
1/22
Siemens AG 2006
Distance Protection
for transmission lines: part 1
Gustav Steynberg
7/31/2019 01_Dist_Part_1
2/22
Page 2 Jul-06
Siemens AG 2006
Power Transmission and DistributionAuthor
Why impedance protection?
Situation: Meshed network and two infeedsDirectional overcurrent time relays
0,6s
0,6s
0,3s
0,3s
0,6s
0,6s
0,3s
0,3s
non-selective trip
7/31/2019 01_Dist_Part_1
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Page 3 Jul-06
Siemens AG 2006
Power Transmission and DistributionAuthor
Localization of short-circuits by means of an impedancemeasurement:
fault on the protected line
fault outside the protected line
Z1
relay A
selectivity
relay A
Z2
Basic principle of impedance protection
7/31/2019 01_Dist_Part_1
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Page 4 Jul-06
Siemens AG 2006
Power Transmission and DistributionAuthor
Distance measurement (principle)
6 loops: 3 phase- phase loops and3 phase- ground loops
phase- phase -loop:
The same applies to the remaining loops
UL1-L2 =
ZL (
IL1 -
IL2)
Measured current
measured voltage
06.08.97dtgerdis3
ZL = RL + j XL
ZE = RE +j XE
IL1
IL2
IL3
IE
Z
L
Z
EUL1UL2UL3
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Page 5 Jul-06
Siemens AG 2006
Power Transmission and DistributionAuthor
phase-ground-loop:UL1 = L1 ( RL + j XL )- E ( RE +j XE)
L1, E measured current
UL1 measured voltage
06.08.97dtgerdis3
The same applies to the remaining loops
Distance measurement (principle)
IL1
IL2
IL3
IE
ZL
ZE
UL1UL2UL3
ZL = RL + j XL
ZE =
RE +j
XE
7/31/2019 01_Dist_Part_1
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Page 6 Jul-06
Siemens AG 2006
Power Transmission and DistributionAuthor
Load and short-circuit impedances
ZLZLF1
ZLF2
RF RF
ZLoadD
F1 F2
X
R
ZL
ZLF2
j SC1j SC2
j L
RR
ZF1
ZF2
RR
ZLoad
ZLF1
Fault area
distance relayoperating
characteristic
Fault in
reverse
direction Load area
Minimum Load Impedance:Minimum voltage 0,9 Un
Maximum current 1,1 In
Maximum angle 30
Phase - Phase Fault
RR RF / 2
Phase - Earth Fault
RR RF /(1 + RE/RL)
7/31/2019 01_Dist_Part_1
7/22Page 7 Jul-06
Siemens AG 2006Power Transmission and DistributionAuthor
Principle of (analog) distance relaying
ISC
E
comparator
ZL
ZSC
ZReplica (line replica impedance)
(corresponds to the set zone reach)
U1= k1 USC= k1 ISCZSC.
U2=k2
ISCZReplica
ZS
Relay design:operation if
U1< U2i.e. ZSC< ZReplica
ZReplicaX
R
Ext. fault
Internal fault
A B
7/31/2019 01_Dist_Part_1
8/22Page 8 Jul-06
Siemens AG 2006Power Transmission and DistributionAuthor
Typical distance zone-characteristic
MHO-circle
shifted circle
polarisedMHO-circle quadrilateral
ZR
ZSC
ZSC'
externalfault
internalfault
X
R
X
R
ZS = 0
ZS small
ZS high ZS
RF
ZL
X
R
centre
ZSC
'
ZSC
settable arccompensation
X
XA
ZSC-L Rarc
RRA
7/31/2019 01_Dist_Part_1
9/22Page 9 Jul-06
Siemens AG 2006Power Transmission and DistributionAuthor
Graded distance zones
time
D1 D2 D3
t1
t2
t3
Z1
Z2
Z3
distance
t = grading time
A CB D
Z1 = 0,85 ZAB
Z2 = 0,85 (ZAB + 0,85 ZBC)
Z3 = 0,85 (ZAB + 0,85 (ZBC + 0,85 ZCD))
Safety margin is 15%: line error
CT, VT error
measuring error
Grading rules:
7/31/2019 01_Dist_Part_1
10/22Page 10 Jul-06
Siemens AG 2006Power Transmission and DistributionAuthor
2nd Zone: It must initially allow the 1st zone on the neighbouring feeder(s) to clear the fault.The grading time therefore results from the addition of the following times:
operating time of the neighbouring feeder mechanical 25 - 80 msstatic: 15 - 40digital: 15 - 30
+circuit breaker operating time HV / EHV: 60 ms (3 cycles) / 40 ms (2 cycles)MV up to about 80 ms (4 cycles)
+distance relay reset time mechanical: approx. 60-100 msstatic: approx. 30 msdigital: approx. 20 ms.
+errors of the distance relay internal timers mechanical: 5% of the set time, minimum 60-100 msstatic: 3% of the set time, minimum 10 msdigital: 1% of the set time, minimum 10 ms
+distance protection starting time *) mechanical: O/C starter: 10 ms, impedance starter: 25 msstatic: O/C stater: 5 ms, impedance starter: 25 ms
digital: generally 15 ms
+ safety margin (ca.) grading; mechanical-mechanical: 100 msstatic/digital-mechanical or vice versa: 75 msdigital-digital or static-static 50 ms
*) only relevant if the set relay times relate to the instant of fault detection / zone pick-up. This is the case withall Siemens relays. There are other relays where the time is adapted by software to relate to the instant of faultinception. In the latter case the starting time has to be dropped.
Determination of grading times(With numerical relays 250 ms is possible)
7/31/2019 01_Dist_Part_1
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Siemens AG 2006Power Transmission and DistributionAuthor
SC
Current area forforward faults
SC
Current area forreverse faults
SC
USC
R
ZSC
Z'SC
Impedance area forforward faults
Impedance area forreverse faults
X
SC
Determination of fault direction
current / voltage diagram impedance diagram
Fault location Where is the fault ?
The impedance also shows the direction, but ....
7/31/2019 01_Dist_Part_1
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Siemens AG 2006Power Transmission and DistributionAuthor
direction may be determined together with the impedance measurementbut: problems may arise in certain cases (e.g. close-in faults)
separate directional determination required!
Why impedance measurement and directional determination separately?
line characteristic
fault with arc resistancein forward direction
fault in forward direction
fault in reversedirection
close-in fault
X
R
A B
Impedance measurement and directional determination
7/31/2019 01_Dist_Part_1
13/22Page 13 Jul-06
Siemens AG 2006Power Transmission and DistributionAuthor
Alternatives for the directional measurement
faulty phase voltage
Vf
If
VL2
VL3
voltage memory(pre-fault voltage)
If
VL2VL3
VL1
healthy-phase voltage(phase to phase voltage)
If
Vf
VL2-L3 VL2VL3
~~
~
~~
~
~~
~
ZlineZgrid relay
fault L1-E
Method 1 Method 2
VL1
VL1Vf
7/31/2019 01_Dist_Part_1
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Siemens AG 2006Power Transmission and DistributionAuthor
Directional measurementSummery of all 3 methods
uRI
= uL2-L3
uf= uL1
Distance measurement
Direction measurementwith voltage memory
Direction measurementwith unfaulted voltage
if(t)u
L1
if
if
if
uL2-L3
uL1
06.08.97dtgerdis9
Measuringwindow
7/31/2019 01_Dist_Part_1
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Siemens AG 2006Power Transmission and DistributionAuthor
Fault detection techniques
Over-current fault detectionVoltage dependantover-current fault detection
Voltage and
angle dependantover-currentfault detection
I
U
I >>I > I >
R
X
Impedancefaultdetection
Not in 7SA522
7/31/2019 01_Dist_Part_1
16/22Page 16 Jul-06
Siemens AG 2006Power Transmission and DistributionAuthor
110 kVnet SCC(3)" = 1500 MVA
40 MVAuSC = 15 %20 kV
400/1 A
l
I>start = 1,5 IN = 600 A
D
OH-line95/15 Al/St
Z'L = 0,483 /km
' l)
10 20 30 40 50 60
I>start= 600 A
0,5
1,0
1,5
2,0
2,5
ISC(2)[kA]
l [km]
ISC(2)=UN 1,1
2 (ZS +ZS +ZL
reach of OC starterapprox. 32 km
N T
Reach of over-current fault detection
ph-ph fault as an example
There is a limitation
to the reach
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Page 17 Jul-06
Siemens AG 2006Power Transmission and DistributionAuthor
II>>I>
UI>>
UI>
UN
Udigital
electro-mechanical
Powersystem
Relay
line
E
E
ZSUSC
ZSCISC
USC
SC
USC
G
G
Voltage controlled overcurrent fault detection
7/31/2019 01_Dist_Part_1
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Page 18 Jul-06
Siemens AG 2006Power Transmission and DistributionAuthor
Voltage and angle controlled overcurrent fault detection(U-I- -starting)
50 %
100 %
U/UN
I/IN1 2 3
I> I> I>>
U(I>) U(I>>)
X X
R R
2
11
2
This method is used in Germany
7/31/2019 01_Dist_Part_1
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Page 19 Jul-06
Siemens AG 2006Power Transmission and DistributionAuthor
X
R
LoadLoad
Z1
Z2
Z4
Z3
Z1B
Z5
Line
Impedance zones of digital relays (7SA6 and 7SA52)
Distance zones
Inclined with line angle
Angle a prevents overreach of
Z1 on faults with fault
resistance that are fed from
both line ends
Fault detection
no fault detection polygon: the
largest zone determinesthe fault detection
characteristic
simple setting of load
encroachment area with
Rmin and Load
7/31/2019 01_Dist_Part_1
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Page 20 Jul-06
Siemens AG 2006Power Transmission and DistributionAuthor
Zone grading chart, radial feeder
D
A
D
B
D
C
>>
D
>t
ZT
Z1
Z2
Z3
Z1 = 0.85 ZA-B
Z3 = 0.85 [ ZA-B + 0.85 (ZB-C+ 0.85 ZC-D) ]
Z2 = 0.85 (ZA-B + 0.85 ZB-C)
Grading according
the recommendation
with the safety margin
of 15%.
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Page 21 Jul-06
Siemens AG 2006Power Transmission and DistributionAuthor
Ring feeder: with grading against opposite end
0.6
0.3
grading time(s)
The same grading from both sides
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Page 22 Jul 06
Siemens AG 2006Power Transmission and DistributionAuthor
Grading in a branched radial system
L2
L3
L4
L1
Z2
Z1
Z3
The impedances of the Z2 and Z3 must be grading with the shortest impedance