ABB REF615 - Earth-Fault Protection

5.2 Earth-fault protection
5.2.1 Non-directional earth-fault protection EFxPTOC
5.2.1.1 Identification
Table 61: Function identification
Different stages: Low stage High stage Instantaneous
stage
IEC 61850 identification: EFLPTOC EFHPTOC EFIPTOC
IEC 60617 identification: I
0
> I
0
>> I
0
>>>
ANSI/IEEE C37.2 device number: 51N-1 51N-2 50N/51N
5.2.1.2 Functionality
The earth-fault function EFxPTOC is used as non-directional earth-fault protection
for feeders.
The function starts and operates when the residual current exceeds the set limit. The
operate time characteristic for low stage EFLPTOC and high stage EFHPTOC can
be selected to be either definite time (DT) or inverse definite minimum time (IDMT).
The instantaneous stage EFIPTOC always operates with the DT characteristic.
In the DT mode, the function operates after a predefined operate time and resets when
the fault current disappears. The IDMT mode provides current-dependent timer
characteristics.
The function contains a blocking functionality. It is possible to block function outputs,
timers or the function itself, if desired.
5.2.1.3 Application
EFxPTOC is designed for protection and clearance of earth faults in distribution and
sub-transmission networks where the neutral point is isolated or earthed via a
resonance coil or through low resistance. It also applies to solidly earthed networks
and earth-fault protection of different equipment connected to the power systems,
such as shunt capacitor bank or shunt reactors and for back-up earth-fault protection
of power transformers.
Many applications require several steps using different current start levels and time
delays. EFxPTOC consists of three different protection stages:
1MRS756378 D Section 5
Protection functions
REF615 145
Application Manual