CHAPTER 8: APPLICATION OF SETTINGS CHANNEL ASYMMETRY COMPENSATION USING GPS
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 8-11
8
contact with the BLOCK GPS TIME REF setting.
2. Create FlexLogic similar to that shown as follows to block the 87L element on GPS loss if step change in the channel
delay occurs during GPS loss conditions or on a startup before the GPS signal is valid. For three-terminal systems, the
87L DIFF 1 TIME CHNG operand must be ORed with the 87L DIFF 2 TIME CHNG FlexLogic operand. The Block 87L (VO1)
output is reset if the GPS signal is restored and the 87L element is ready to operate.
3. Assign virtual output BLOCK 87L (VO1) to the 87L Current Differential Block setting (
SETTINGS  GROUPED ELEMENTS 
SETTING GROUP  LINE DIFFERENTIAL...  CURRENT DIFFERENTIAL  CURRENT DIFF BLOCK
). It can be used to enable
backup protection, raise an alarm, and perform other functions as per the given protection philosophy.
8.3.3 Compensation method 2
Enable GPS compensation on the loss of the GPS signal at any terminal and block the 87L element after a specified time.
This is a simple and conservative way of using the GPS feature. Follow steps 1 and 3 in compensation method 1. The
FlexLogic is simple: 87L DIFF GPS FAIL-Timer-Virtual Output Block 87L (VO1). It is recommended that the timer be set no
higher than 10 seconds.
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