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GE P444

GE P444
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Application Notes
P44x/EN AP/Hb
6
MiCOM P40 Agile P442, P444
(AP) 5-
31
mutual coupling may be large, and either must be factored into the settings, or
accommodated by measurement of the parallel, mutually-coupled lines residual (earth)
current, where zero-sequence current information is available. The value of the residual
currents from parallel lines is then integrated into the distance measurement equation.
The relay is capable of measuring and using mutually-coupled residual current information
from parallel lines. The mutual current is measured by a dedicated analogue input.
2.7 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 earth 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.
FaultDirectionLoop_AN =
)
I.
V
(
n
n0
A
AN
and FaultDirectionLoop_BN =
)I.V(
n
n0
BBN
Z
1 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.
Protection against Current Reversal (Transient Blocking)
When a fault occurs on a line, which is parallel to the protected line, the pilot schemes on the
protected line may be subjected current reversals from sequential clearing on the parallel
line. A fault on the parallel line may start by appearing external to the protected line in the
reverse direction, and then, after a sequential operation of one of the parallel line circuit-
breakers, the fault appears forward. This situation can affect security of certain channel-
aided schemes on the protected line.

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