Impedance Phase Selection - GE MiCOM P40 Agile Technical Manual

P44x/EN AP/Hb6
(AP) 5-24
2.3.3 Phase Selection
If the fault currents are high enough with respect to the maximum load currents current-
based phase selection is used; if not, impedance-based phase selection is required.
Current Phase Selection
Amplitudes I'A, I'B, I'C are derived from the three measured phase currents IA, IB, IC. These
values are then compared to each other and to the two thresholds S1 and S2:
• First threshold is S1= 3 x I'n
• Second threshold is S2 = 5 x I'n
Example:
If I'A< I'B < I' C:
• If I'
> S2 and I'
C
• If I'
> S2, I'B > S1 and I'
C
• If I'
> S2 and I'
C
• If I'
< S2, the current phase selection cannot be used. Impedance phase selection
C
should then be used.

Impedance Phase Selection

Impedance phase selection is obtained by checking the convergence of the various
measuring loops within the start-up characteristic, as follows:
• T
• Z
AN
• Z
BN
• Z
CN
• Z
AB
• Z
BC
• Z
CA
In addition, the following are also defined:
• R
= Z
AN
• R
= Z
BN
• R
= Z
CN
• R
= Z
AB
• R
= Z
BC
• R
= Z
CA
> S1, the fault is three-phase.
A
< S1, the fault is two-phase, on phases B and C.
A
< S1, the fault is single-phase, on phase C.
B
= Presence of zero-sequence voltage or current (logic Information: 0 or 1).
= Convergence within the characteristic of the loop A (logic Information).
= Convergence within the characteristic of the loop B (logic Information).
= Convergence within the characteristic of the loop C (logic Information).
= Convergence within the characteristic of the loop AB (logic Information).
= Convergence within the characteristic of the loop BC (logic Information).
= Convergence within the characteristic of the loop CA (logic Information).
Z
x where ZBC = convergence within the characteristic of the loop
BC
AN
BC (Logic Information).
Z
x where ZCA = convergence within the characteristic of the loop
CA
BN
CA (Logic Information).
Z
x where ZAB = convergence within the characteristic of the loop
AB
CN
AB (Logic Information).
Z
x where ZCN = convergence within the characteristic of the loop
CN
AB
C (Logic Information).
Z
x where ZAN = convergence within the characteristic of the loop
AN
BC
A (Logic Information).
Z
x where ZBN= convergence within the characteristic of the loop
BN
CA
B (Logic Information).
Application Notes
MiCOM P40 Agile P442, P444