9-8 L30 Line Current Differential System GE Multilin
9.3 CHANNEL ASYMMETRY COMPENSATION USING GPS 9 APPLICATION OF SETTINGS
9
3. Assign virtual output BLOCK 87L (VO1) to the 87L Current Differential Block setting. It can be used to enable backup
protection, raise an alarm, and perform other functions as per the given protection philosophy.
9.3.3 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 Flex-
Logic™ 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.
9.3.4 COMPENSATION METHOD 3
Continuously operate the 87L element but enable GPS compensation only when valid GPS signals are available. This pro-
vides less sensitive protection on GPS signal loss at any terminal and runs with higher pickup and restraint settings.
This approach can be used carefully if maximum channel asymmetry is known and doesn't exceed certain values (2.0 to
2.5 ms). The 87L DIFF MAX ASYM operand can be used to monitor and signal maximum channel asymmetry. Essentially,
the L30 switches to another setting group with higher pickup and restraint settings, sacrificing sensitivity to keep the 87L
function operational.
1. Create FlexLogic similar to that shown below to switch the 87L element to Settings Group 2 (with most sensitive set-
tings) if the L30 has a valid GPS time reference. If a GPS or 87L communications failure occurs, the L30 will switch
back to Settings Group 1 with less sensitive settings.
831777A1.CDR
1
87L DIFF GPS FAIL
2
87L DIFF BLOCKED
3
AND(2)
AND(2)
4
87L DIFF GPS FAIL
5
87L DIFF 1 TIME CHNG
6
AND(2)
AND(2)
7
TIMER 1
8
OR(2)
OR(2)
9
87L DIFF BLOCKED
10
NOT
11
87L DIFF GPS FAIL
12
NOT
13
AND(2)
AND(2)
14
TIMER 2
15
LATCH
Reset
Set
LATCH
16
= BLOCK 87L (VO1)
= BLOCK 87L (VO1)
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