ABB RED615 Technical Manual page 289

1YHT530004D05 D
615 series
Technical Manual
A070441 V1 EN
Figure 138: Earth-fault situation in an isolated network
Directional earth-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 IEDs. 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 "IoSin" or
"Phase angle". Figure 139
compensated network with an earth fault in phase C.
A070444 V2 EN
Figure 139: Earth-fault situation in a compensated network
The Petersen coil or the earthing resistor may be temporarily out of operation. To
keep the protection scheme selective, it is necessary to update the characteristic
angle setting accordingly. This can be done with an auxiliary input in the relay
which receives a signal from an auxiliary switch of the disconnector of the Petersen
illustrates a simplified equivalent circuit for a
Section 4
Protection functions
283