8-8
L30 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
CHANNEL ASYMMETRY COMPENSATION USING GPS
CHAPTER 8: APPLICATION OF SETTINGS
8
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.
8.3.4 Compensation method 3
Continuously operate the 87L element but enable GPS compensation only when valid GPS signals are available. This
provides 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 does not 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 as follows to switch the 87L element to Settings Group 2 (with most sensitive
settings) if the L30 has a valid GPS time reference. If a GPS or 87L communications failure occurs, the L30 switches
back to Settings Group 1 with less sensitive settings.
2.
Set the 87L element with different differential settings for Settings Groups 1 and 2 shown as follows.
3.
Enable GPS compensation when the GPS signal is valid and switch to Settings Group 2 (with more sensitive settings),
shown as follows.
