I
neg
=
1
3
⋅
| (
I
A
+ a
2
I
B
+ aI
C
) |
Phase sequence A-C-B:
I
neg
=
1
3
⋅
| (
I
A
+ aI
B
+ a
2
I
C
) |
a = e
j120°
a
2
= e
j240°
The negative-sequence current is monitored by the P631 to detect when it
exceeds the set thresholds. Alternatively, two different thresholds 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. The IDMT protection will trigger when the
1.05-fold of the set reference current value is exceeded. Dependent on the
characteristic selected and the negative-sequence current magnitude the P631
will determine the tripping time. Furthermore, a minimum tripping time can be
set; the tripping time will not fall below this minimum independent of the
magnitude of the current.
The negative-sequence current stage of the IDMT protection function can
optionally be blocked by the inrush stabilization function of differential
protection.
3 Operation
P631
P631/EN M/R-11-C // P631-310-650 3-139
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