ABB Relion 615 series, Technical Manual

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A B C
C
0
-
Σ I
01
Σ I
02
-
Σ I
02
I
ef
R
0
0
V
0
V
0
V
A070441-ANSI V1 EN
Figure 155: Ground-fault situation in an isolated network
Directional ground-fault protection in a compensated network
In compensated networks, the capacitive fault current and the inductive resonance coil
current compensate each other. The protection cannot be based on the reactive current
measurement, since the current of the compensation coil would disturb the operation of
the protection relays. In this case, the selectivity is based on the measurement of the active
current component. The magnitude of this component is often small and must be increased
by means of a parallel resistor in the compensation equipment. When measuring the
resistive part of the residual current, the relay characteristic angle (RCA) should be set to
0 degrees and the operation criteria to "IoCos" or "Phase angle".
Figure 156 illustrates a
simplified equivalent circuit for a compensated network with a ground fault in phase C.
A B C
C
0
Σ I
01
Σ I
02
-
Σ I
02
I
ef
R
0
L R
L
-
Σ I
01
0
V
0
V
0
V
A070444-ANSI V1 EN
Figure 156: Ground-fault situation in a compensated network
Section 4
1MAC059074-MB A
Protection functions
336 615 series ANSI
Technical Manual