G. Ziegler. Digital Differential Protection
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G. Ziegler, 10/2005 page 205
Differential Protection Symposium
Belo HorizonteNovember 2005
Conclusions
ü Combined distance and differential protection relays , together with
modern comms, allow to enhance line protection in a cost saving way.
üThe dissimilar protection principles complement each other perfectly.
üDistance and differential protection can both be configured as phase
segregated teleprotectionschemes allowing absolute phase selective fault
clearance and autoreclosureeven with complex cross county and inter-
circuit faults.
üDigital relay to relay commsallows to exchange data for upgraded two
sided fault locating.
üUsing a single relay type for distance and/or differential protection also
saves on cost in investment and operation.
G. Ziegler, 10/2005 page 206
Differential Protection Symposium
Belo HorizonteNovember 2005
∆ i
1
(t)=i
1
(t)-i
1
(t -2T)
PCP
7SD512
i1(t)
Sign.{ ∆i
1
}
−
+
−
+
−
+
−
+
i2(t)
I1I2
PCP
7SD512
∆ i
1
(t)=i
1
(t)-i
1
(t -2T)
Sign.{ ∆i
2
}
7SD51: Phase comparison,
Dynamic supplement based on delta-quantities
G. Ziegler, 10/2005 page 207
Differential Protection Symposium
Belo HorizonteNovember 2005
PVS
7SD512
i1(t)
−
+
−
+
−
+
−
+
i2(t)
−
+
−
+
−
+
−
+
I1I2
i1(t)
−
+
−
+
i2(t)
−
+
−
+
I1I2
−
+
−
+
−
+
−
+
no coincidenceno coincidence
TrippingTripping
PVS
7SD512
PVS
7SD512
PVS
7SD512
External fault
Internal fault,
7SD51: Phase comparison
Full coincidence
Full coincidence
G. Ziegler, 10/2005 page 208
Differential Protection Symposium
Belo HorizonteNovember 2005
ϕ
I
1
-I
2
I
C
I
1
=I
L
+I
C
-I
2
= I
L
I
C
E1
I
L
E2
ϕ
ϕ
KO
-I
2
I
2
I
1
undefined range due to
discrete sampling :
±1/2∆T = ±1,66/2 ms= ±15
O
Tripping
range
undefined
range
Phase shift ϕ caused by
charging current I
C
7SD51: Phase comparison: Impact of charging current
G. Ziegler, 10/2005 page 209
Differential Protection Symposium
Belo HorizonteNovember 2005
− + + +
Sampling interval (1,66 ms)
Telegram acc. to IEC 60870-5
Hamming distance d= 4
01
00
11
START 1 1 ···1 0 1 CHECK END
4 directional signs per phase = 12 binary digits
Sign.{ i(t) }
i(t)
Phase comparison protection 7SD51:
Sampling of the rectangular sign wave and data transmission telegram
G. Ziegler, 10/2005 page 210
Differential Protection Symposium
Belo HorizonteNovember 2005
Total situation after fault inception:
Load before fault inception:
Pure fault part :
E
1
E
2
Z
V2
Z
V1
I
1
I
2
R
F
Z
V2
Z
V1
I
1L
I
2L
U
FL
∆I
1
=I
1F
∆I
2
=I
2F
Z
V2
Z
V1
U
FL
R
F
∆I
1
, ∆I
2
: DELTA-quantities
∼
∼
E
1
∼
E
2
∼∼
Measurement based on delta quantities, Principle
G. Ziegler, 10/2005 page 217
Differential Protection Symposium
Belo HorizonteNovember 2005
Digital BusbarProtection
Gerhard Ziegler
G. Ziegler, 10/2005 page 218
Differential Protection Symposium
Belo HorizonteNovember 2005
Res
Ik ⋅
Op
I
1
2
n
Busbar
I
op
>
I
op
I
Res
k %
Tripping
area
Busbardifferential protection, Principle
(Analogtechnique)
Measuring
circuit
Operating
characteristic
G. Ziegler, 10/2005 page 219
Differential Protection Symposium
Belo HorizonteNovember 2005
IΣ
IΣ
1
2
n
=
=
7SD601
1,9 mA
=
/IN
100mA
∼
/IN
7TM70
4AM
33
3
Part-digital Busbarprotection 7SS6
G. Ziegler, 10/2005 page 220
Differential Protection Symposium
Belo HorizonteNovember 2005
I
A
I
S
Internal faults (k=1)
Relay characteristic
k= 0.25 to 0.8
I
d
>
7SS6: Operating characteristic