where:
maxIph is the maximal current magnitude found in any of the three phases
INRelPG
is the setting of 3I0 limit for release of phase-to-ground measuring loop in % of
IBase
IBase
is the global setting of the base current (A)
In systems where the source impedance for zero sequence is high the change of zero sequence
current may not be significant and the above detection may fail. In those cases the detection
enters the second level, with evaluation of zero and negative sequence voltage. The release of the
ground-fault loops can then be achieved if all of the following conditions are fulfilled:
|3V
0
|>|V
2
| × 0.5
|3V
0
|>V
1
| × 0.2
|V
1
|> VBase × 0.2/√(3)
and
3I
0
<0.1 × IBase
or
3I
0
<maxIph ×
INRelPG
where:
3V
0
is the magnitude of the zero sequence voltage
V
2
is the magnitude of the negative sequence voltage at the relay measuring point
k5 is design parameter
ILmax is the maximal phase current
IMinOp
is the setting of minimum operate phase current in % of
IBase
Phase-to-phase fault detection
SEMOD153832-119 v2
The detection of phase-to-phase fault is performed by evaluation of the angle difference between
the sequence voltages V
2
and V
1
.
Section 7 1MRK 502 066-UUS B
Impedance protection
246
Technical manual
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