Channel Asymmetry Compensation Using Gps; Introduction; Compensation Method 1 - GE L90 Instruction Manual

CHANNEL ASYMMETRY COMPENSATION USING GPS

8.3 Channel asymmetry compensation using GPS

8.3.1 Introduction

As indicated in the Settings chapter, the L90 provides three basic methods of applying channel asymmetry compensation
using GPS. Channel asymmetry can also be monitored with actual values and an indication signalled (FlexLogic operands
87L DIFF 1(2) MAX ASYM
philosophy, the relay can be programmed to perform the following on the loss of the GPS signal:
• Enable GPS compensation on the loss of the GPS signal at any terminal and continue to operate the 87L element
(using the memorized value of the last asymmetry) until a change in the channel round-trip delay is detected.
• Enable GPS compensation on the loss of the GPS signal at any terminal and block the 87L element after a specified
time.
• Continuously operate the 87L element but only enable GPS compensation when valid GPS signals are available. This
provides less sensitive protection on the loss of the GPS signal at any terminal and runs with higher pickup and
8
restraint settings.

8.3.2 Compensation method 1

Enable GPS compensation on the loss of the GPS signal at any terminal and continue to operate the 87L element until a
change in the channel round-trip delay is detected.
If GPS is enabled at all terminals and the GPS signal is present, the L90 compensates for the channel asymmetry. On the
loss of the GPS signal, the L90 stores the last measured value of the channel asymmetry per channel and compensates for
the asymmetry until the GPS clock is available. However, if the channel was switched to another physical path during GPS
loss conditions, the 87L element must be blocked, since the channel asymmetry cannot be measured and system is no
longer accurately synchronized. The value of the step change in the channel is preset in the L90
menu and signaled by the
1. Enable channel asymmetry compensation (
8-10
Figure 8-5: Distributed bus protection
asserted) if channel asymmetry exceeds preset values. Depending on the implemented relaying
FlexLogic operand. To implement this method, use the following steps:
87L DIFF 1(2) TIME CHNG
CHNL ASYM COMP
CHAPTER 8: APPLICATION OF SETTINGS
) by setting it to ON. Assign the GPS receiver failsafe alarm
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
settings
POWER SYSTEM