CHAPTER 6: SETPOINTS
S3 PROTECTION
345 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
6–45
Transformer instantaneous differential (50/87)
The 345 relay provides one Instantaneous Differential element per setpoint group.
Instantaneous Differential protection is not biased protection and operates in a fashion
similar to instantaneous overcurrent protection. Inputs to this protection are computed on
the basis of the relay per-phase differential currents. Operation occurs if the value of any
of the computed phase differential currents is above the instantaneous differential pickup
setting.
Instantaneous Differential protection is usually set to operate during high-fault current
situations, and if used, its pickup is set according to the following criteria:
•
The pickup setting (xCT) is selected to be higher than the maximum inrush current
during transformer energization
•
The pickup setting is set higher than the fault current for faults occurring outside the
zone of protection
•
The pickup setting is selected to be lower than the maximum fault current during
internal fault conditions.
PATH:
SETPOINTS > S3 PROTECTION > S3 PROTECTION GROUP 1(2) > XFMR INST DIFF
INST DIFF FUNCTION
Range: Disabled, Latched Alarm, Alarm, Trip
Default: Disabled
For details see
Common setpoints
.
The output relays #1 “R1 TRIP” and #2 “R2 TRIP” will operate, when the
Trip
setting is
selected, and the Instantaneous Differential protection is operational.
INST DIFF PICKUP
Range: 3.00 – 20.00 xCT in steps of 0.01 xCT
Default: 8.00xCT
This setting defines the pickup level of the differential current required for operation.
OUTPUT RELAY X
For details see
Common setpoints
.
INST DIFF BLOCK1/2/3
For details see
Common setpoints
.
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