Areva MiCOM P441, Техническое руководство

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Relay Description P44x/EN HW/E33
MiCOM P441/P442 & P444 Page 27/44
4.2.5 Phase Selection
Phase selection is made on the basis of a comparison between the transition values for the
derivatives of currents IA, IB and IC:
∆
I'A,
∆
I'B,
∆
I'C,
∆
I'AB,
∆
I'BC,
∆
I'CA
NOTE: The derivatives of the currents are used to eliminate the effects of the
DC current component.
Hence:
∑
+ ≥
∆ =
4 0
0
i
A AN
)² ' ( S
n ni
n
I
∑
+ ≥
∆ =
4 0
0
i
AB
)² ' ( S
n ni
n
AB
I
∑
+ ≥
∆ =
4 0
0
i
B BN
)² ' ( S
n ni
n
I
∑
+ ≥
∆ =
4 0
0
i
BC
)² ' ( S
n ni
n
BC
I
∑
+ ≥
∆ =
4 0
0
i
C CN
)² ' ( S
n ni
n
I
∑
+ ≥
∆ =
4 0
0
i
CA
)² ' ( S
n ni
n
CA
I
The phase selection is valid if the sum (SAB+SBC+SCA) is higher than a threshold. This
sum is not valid if the positive sequence impedance on the source side is far higher than the
zero sequence impedance. In this case, the conventional algorithms are used to select the
faulted phase(s).
Sums on one-phase and two-phase loops are performed. The relative magnitudes of these
sums determine the faulted phase(s).
For examples, assume :
If SAB<SBC<SCA and If SAB<<SBC, the fault has had little effect on the loop A to B. If
SAN<SBN<SCN , the fault declared as single phase fault C.
If the fault is not detected as single-phase by the previous criterion, the fault conditions are
multi-phase.
If SAN<SBN<SCN and If SAB<<SBC, the fault is B to C.
If SAN<SBN<SCN and If SAB•SBC•SCA and if SAN•SBN•SCN, the fault is three-phase (the
fault occurs on the three phases).
4.2.6 Summary
A transition is detected if
∆
I > 20% x In or
∆
V >10% x Vn
Then three tasks are starting in parallel:
•
Fault confirmation :
∆
I and
∆
V (3 consecutive samples)
•
Faulty phase selection (4 consecutive samples)
•
Fault directional decision (5 consecutive samples)