Areva MiCOM P441, Technical Manual

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P44x/EN HW/E33 Relay Description
Page 38/44 MiCOM P441/P442 & P444
Where:
kr = an adjustable coefficient for residual or zero sequence current (3 x I0),
ki: = an adjustable coefficient for negative sequence current (I2),
Imax(t): maximum instantaneous current detected on one phase (A, B or C),
IN: nominal current
4.7.5 Fault Detection after Single-phase Tripping (one-pole-open condition)
After a circuit breaker pole has opened, there is no current and voltage on the applicable
phase, which allows the protection unit to detect whether a one-pole cycle of the voltage
transformer are on a line side.
The reception of «poles discrepancy» input signal allows the protection unit to detect one-
pole-open condition blocking if the voltage transformer is on the bus side.
If another fault appears during a one-pole cycle or just after the voltage has been restored on
the applicable phase, direction is defined and phase selection performed.
4.8 Double Circuit Lines
Double circuit lines must be taken into account in the operating principle of the protection
scheme to avoid unwanted tripping of «sound» phases, which could be the result of an
excessively general phase selection.
Phase selection for an inter-circuit fault
During a two-phase fault selection, for example on loop AB, the P44x checks direction on the
two adjacent ground loops, (A to Neutral and B to Neutral). The direction is determined
using either the conventional algorithm or the high-speed algorithm (using superimposed
quantities), depending on fault severity. If superimposed components are used, the
transient (fault) energy is summated phase by phase.
( )
∑
∆ ∆ =
n
n
A AN AN
I V tionLoop FaultDirec
0
_
.
and
( )
∑
∆ ∆ =
n
n
B BN BN
I V tionLoop FaultDirec
0
. _
Z1 BN fault
AN
BN
P3040ENa
Z1 AN fault
Trip single pole Trip single pole
The directions of the two adjacent ground loops are compared, as follows:
•
If the two directions are forward, the fault is a two-phase fault on the protected line.
•
If only one of the directions is forward, for instance Sa, the fault is single-phase
(A to Neutral) on the protected line.
•
If the two directions are reverse, the fault is not on the protected line.