Condition 1 and Condition 2 ⇒ Fault type
CG CG CG
BG AG BCG
The sequence phase selector is blocked when ground is not involved or if a three-phase fault is
detected.
Three-phase fault detection
SEMOD153832-174 v4
Unless it has been categorized as a single or two-phase fault, the function classifies it as a three-
phase fault if the following conditions are fulfilled:
|V
1
|
V1Level
and
|I
1
|>
I1LowLevel
or
|I
1
|>
IMaxLoad
where:
V
1
| and |I
1
| are the positive sequence voltage and current magnitude
V1Level
,
I1LowLevel
are the setting of limits for positive sequence voltage and current
IMaxLoad
is the setting of the maximum load current
The output signal for detection of three-phase fault is only released if not ground fault and phase-
to-phase fault in the main sequence function is detected.
The conditions for not detecting ground fault are the inverse of equation 5 to 10.
The condition for not detecting phase-to-phase faults is determined by three conditions. Each of
them gives condition for not detecting phase-to-phase fault. Those are:
1:
ground fault is detected
or
|3I
0
|> 0.05 ·
IBase
and
|3I
0
|>maxIph ·
INRelPG
2:
phase-to-ground and phase-to-phase faults are not fulfilled
and
maxIph<0.1 ·
IBase
and
Table continues on next page
Section 7 1MRK 502 066-UUS B
Impedance protection
250
Technical manual
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