ABB Relion 670 series, Technical Manual

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Beta
ç
V3N+V3T
ç
X
a
b
ç
V3N
ç
b
³
a
VT3BlkLevel
a
b
a
³
b
ç
V3T
ç
AND
PU3H
t TRIP3H
VNFundPU
a
b
b
³
a
V_N
PU_VN
TRIPVN
OR
OR
PICKUP
TRIP
ANSI07000001-2-en.vsd
0
t
0
ANSI07000001 V2 EN-US
Figure 357: Simplified Pickup and Trip logical diagram of the 100% Stator earth fault
protection, 3rd harmonic based STEFPHIZ (59THD) protection
There are two different cases of generator block configuration; with or without generator circuit
breaker. If there is no generator breaker the capacitive coupling to ground is the same under all
operating conditions. When there is a generator breaker, the capacitive coupling to ground differs
between the operating conditions when the generator is running with the generator breaker open
(before synchronization) and with the circuit breaker closed. This can be shown as in figure 358 .
-
D
V
3
+
- UV
3
+
- V
3N
+
+
V
3T,A
-
+
V
3T,B
-
+
V
3T,C
-
en07000002-2_ansi.vsd
Ctr/3
Ctr/3
Ctr/3
ANSI07000002 V2 EN-US
Figure 358: Generator block with generator circuit breaker
With the circuit breaker open, the total capacitance will be smaller compared to normal operating
conditions. This means that the neutral point 3
rd
harmonic voltage will be reduced compared to
the normal operating condition. Therefore, there is a possibility to reduce the sensitivity of the
protection when the generator circuit breaker is open.
With the setting
CBexists change of the sensitivity is enabled. If the binary input signal 52a is
activated the set sensitivity is valid. If the generator circuit breaker is opened the binary input 52a
1MRK 502 066-UUS B Section 9
Voltage protection
659
Technical manual