Description of Operation
GARD 8000 Distance Relay
RFL Electronics Inc.
The fault locator uses the phase selector to determine the type of fault. Then the algorithm for each
type of fault determines the distance to the fault.
9.3
PHASE SELECTOR
The phase selector uses two main algorithms. The first determines whether the fault is three-phase.
This requires three simultaneous conditions:
1) High positive sequence component, that is, above 0.1 x In.
2) Low negative sequence current: meaning no more than 0.1 x In A and <10% of the positive-
sequence current.
3) Low zero-sequence current: no more than 0.08 x In and < 8% of the positive sequence
current.
If the fault detected does not fulfill all the conditions of a three-phase fault, the second phase selector
algorithm is executed. It compares the arguments of the negative and positive cycles.
If the fault is not three-phase and meets the third condition for three-phase faults (low zero- sequence
component), it can not be a ground fault. Therefore, it has to be two-phase. If, however, it does not
meet the third condition for three-phase faults (high zero-sequence component), it must be a ground
fault, single-phase or two-phase to ground.
Faulted phases are determined by analyzing the angle:
φ
=
arg
(
Ia
2
)
−
arg
(
Ia
1_
f
)
where:
Ia2: Phase A negative sequence current.
Ia1_f: Faulted phase A positive sequence current (once the load component is eliminated).
The following figures represent the angle diagrams used to determine the phases involved in the fault
by the
φ
angle.
Figure 9-26. Phase selector
August 1, 2009
9-28
973.334.3100
