RFL Electronics GARD 8000, Инструкция по эксплуатации

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Description of Operation
GARD 8000 Distance Relay RFL Electronics Inc.
9.4 FAULT DETECTOR
The distance relay is provided with a fault detector to supervise element operation. Operation of the
fault detector is based on:
9.4.1 DETECTION OF INCREASE OF SEQUENCE CURRENTS
The conditions which activate the fault detector are:
•
An increase of the zero sequence current with respect to the value two cycles previously, and
higher than 0.04 times nominal current.
•
And increase of the negative sequence current with respect to the value two cycles previously,
and higher than 0.04 times nominal current.
•
More than 25% increase of the positive sequence current with respect to the value two cycles
previously.
The fault detector will remain sealed for two cycles, plus an additional reset time of 30 ms. The fault
detector is also kept sealed by assertion of any of the distance elements, overcurrent elements, stub
bus, close into fault, and the trip signal.
9.5 LOSS-OF-POTENTIAL BLOCK
If the PT secondary circuit fuses blow, the terminal unit will lose the corresponding analog voltage
input. This situation may cause unwanted operation of the distance elements. Therefore, this condition
must be detected and the measuring elements must be blocked before undesired tripping occurs.
The Loss-of-potential threshold is 30 V. LOP logic operation is blocked when any breaker pole is open
and if a fault detector is active. The loss-of-potential condition has a drop-out delay set by ‘LOP Reset
time’ to prevent assertion of distance elements when the voltage is restored.
Fault Detector
Any pole open
VA
VB
VC
LOP < 30 V
T
0
LOP (Fuse fail)
LOP Reset time
Figure 9-27. Loss-of-Potential Block
August 1, 2009 9-29 973.334.3100