Loss-of-Potential (LOP) Enable Setting, (LOPE)
Fuses or molded case circuit breakers often protect the secondary windings of the power
system potential transformers. An operation of one or more fuses or molded case circuit
breakers results in a loss of polarizing potential inputs to the relay. Loss of one or more
phase voltages prevents the relay from properly discriminating fault direction.
Because occasional loss-of-potential to the relay is unavoidable, detection of this condition is
desirable. Once a true loss-of-potential condition is detected, you may elect to block distance
element operation and issue an alarm.
The relay discriminates between faults (which may reduce the voltage magnitude(s) to nearly
zero) and loss-of-potential conditions. The following equation shows the loss-of-potential
(LOP) detection logic for the relay:
SET LOP = [47QL * NOT(46QL)]:
Detects the presence of negative-sequence voltage in
the absence of negative-sequence current
+ [NOT(47P) * NOT(50P)]:
Detects the absence of positive-sequence voltage in the
absence of current above the 50P setting
Where:
47QL
≡
Low set negative-sequence overvoltage detector
50QL
≡
Low set negative-sequence overcurrent detector
47P
≡
Low set positive-sequence overvoltage detector
50P
≡
Low set phase overcurrent element
For one or more blown PT fuses, the relay declares a loss-of-potential condition when the
measured negative-sequence voltage exceeds 14 V of V2 and measured negative-sequence
current is below 0.083 A secondary. For three blown PT fuses, the relay declares an LOP
condition when the measured positive-sequence voltage is below 14 V of V1 and the low set
phase overcurrent detector (50P) is not picked up.
You determine how the relay uses loss-of-potential detection by selecting the LOPE setting.
The LOPE setting choices and their associated results are:
N
Relay sets LOP bit when loss-of-potential condition is detected.
Distance and directional elements are not blocked.
Set the LOP bit in a programmable logic mask to indicate condition, if desired.
Y
Relay sets LOP bit when loss-of-potential condition is detected.
Distance elements are blocked and directional elements default forward.
Set the LOP bit in a programmable logic mask to indicate condition, if desired.
1
Relay blocks distance elements and directional elements default forward when
LOP condition is detected.
If the 52A input is asserted while LOP is detected, the Relay Word LOP bit is
asserted.
Date Code 920508
Applications
SEL-221F, -1 Instruction Manual
5-27
Содержание SEL-221F
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Страница 228: ...APPENDICES TABLE OF CONTENTS Parts Placement Diagram Date Code 920508 Table of Contents SEL 221F 1 Instruction Manual i ...
Страница 229: ...SEL 200 Series Relay Main Board Troubleshooting Test Points and Jumper Locations ...