Date Code 20011026
Applications
5-19
SEL-321/321-1 Instruction Manual
The three-phase fault duty for a fault at Bus B is 4456 A. To assure rapid clearance of this fault,
a 50H setting of 2250 A is selected for this example.
Calculations: CTR = 200:1
50H secondary amps =
2250
200
1125
A primary
A
=
.
secondary
The Switch-Onto-Fault logic may be enabled by change in the 52A status showing the breaker
has just closed or by asserting the close input to the relay from the breaker close bus.
The 52A method works well for single or multiple breaker applications.
For a single breaker configuration, using the close bus enable is a better selection. The close
enable delay (CLOEND) should be set less than the shortest reclose open interval. The Switch-
Onto-Fault Delay (SOTFD) determines how long the SOTF logic is allowed to trip after the
breaker is closed.
For our example, the close method is used.
ESOTF = YYYY
ENCLO = YYYY
CLOEND = 10.00
10.00
10.00
10.00
EN52A = NNNN
SOTFD = 30.00
30.00
30.00
30.00
50H = 11.25
11.25
11.25
11.25
- Relay Elements and Other Settings Affected
50H element.
Loss-of-Potential (LOP) Enable Setting (ELOP)
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 voltage 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 LOP condition is detected, you may elect to block distance element
operation, block or enable directional overcurrent elements, and issue an alarm.
Advanced loss-of-potential logic has been added to the relay. This logic requires no settings
other than the choice of enable settings. The use of advanced loss-of-potential logic is
recommended, however the option to use the original loss-of-potential logic and settings has been
retained to maintain compatibility with previous versions of the relay. Settings ELOP = N or Y
use the original loss-of-potential logic. Settings ELOP = N1, Y1, or Y2 use the advanced loss-of-
potential logic.
Содержание SEL-321
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