Micom P631, Technical Manual

Page: 182 / 638

3.22.3 Negative-Sequence Current Stages
The P631 calculates the negative-sequence current from the three phase current
values according to this equation. This is based on the setting at MAIN: Phase
sequence.
Phase sequence A-B-C:
I ̲
neg
=
1
3
⋅
| (
I ̲
A
+ a ̲
2
I ̲
B
+ a ̲ I ̲
C
) |
Phase sequence A-C-B:
I ̲
neg
=
1
3
⋅
| (
I ̲
A
+ a ̲ I ̲
B
+ a ̲
2
I ̲
C
) |
a ̲ = e
j 120°
a ̲
2
= e
j 240°
The negative-sequence current is monitored by the P631 with three-stage
functions to detect when it exceeds the set thresholds. One of two different
threshold types can be active. The “dynamic” thresholds are active for the set
hold time for the “dynamic parameters” (see
Section 3.12.5, (p. 3-76) ) and the
“normal” thresholds are active when no hold time is running. If the current
exceeds the set thresholds in one phase, timer stages are started. Once the time
delays have elapsed, a trip signal is issued. The timer stages can be blocked by
appropriately configured binary signal inputs.
The first stage of the negative-sequence current protection function can
optionally be blocked by the inrush stabilization function of differential
protection.
P631 3 Operation
3-126 P631/EN M/R-11-C // P631-310-650