ABB RELION 620 Series Technical Manual page 214

Section 4
Protection functions
208
A B C
ΣI
V
0
ΣI
A070441-ANSI V1 EN
Figure 92: 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 zero-sequence current, the relay characteristic angle (RCA) should be
set to 0 degrees and the operation criteria to I
A B C
ΣI
ΣI
L R
V
L
0
A070444-ANSI V1 EN
Figure 93: Ground-fault situation in a compensated network
The Petersen coil or the grounding resistor may be temporarily out of operation. To keep
the protection scheme selective, it is necessary to update the Characteristic angle setting
01
C R
0
02
I
ef
cos(φ) or phase angle.
0
01
C R
0
02
I
ef
1MAC504801-IB E
- V
0
0
-
V
0
ΣI
02
-
V
0
0
ΣI
01
-
V
0
ΣI
02
620 series ANSI
Technical Manual