ABB REG670 - Page 546

IEC07000186 V1 EN
Figure 260: Simplified Start and Trip logical diagram of the 100% Stator earth
fault protection, 3rd harmonic based STEFPHIZ 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
earth is the same under all operating conditions. When there is a generator breaker, the
capacitive coupling to earth 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
261.
- DU
3
+
- U
3
+
- U
3N
+
+
U
3T,L1
-
+
U
3T,L2
-
+
U
3T,L3
-
en07000002-2.vsd
Ctr/3
Ctr/3
Ctr/3
IEC07000002 V2 EN
Figure 261: 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
Section 9 1MRK502052-UEN B
Voltage protection
540
Technical manual