Areva MiCOM P125, Technical Manual

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P12y/EN AP/D32 Application Guide
Page 46/74 MiCOM P125/P126 & P127
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If this condition arose, a permanent fault would effectively look like a number of
transient faults, resulting in continuous autoreclose operations unless additional
measures were taken to overcome this, such as excessive fault frequency lockout
protection.
•
A sensitive earth fault protection is usually applied to detect high resistance earth
faults
Usually, a long trip delay time is set, typically 10 - 15 s. This longer time may be taken
into consideration, if autoreclose is started by an earth fault protection, and when
deciding on a reclaim time, if the reclaim time is not blocked by a SEF protection start
signal. Sensitive earth faults, for example, a broken overhead conductor in contact
with dry ground or a wood fence, is rarely transient and presents great danger to
persons and animals. It is therefore common practice to block autoreclose by
operation of sensitive earth fault protection and lockout the circuit breaker.
•
Where motor-wound spring closed circuit breakers are used, the reclaim time must be
at least as long as the spring winding time for high-speed autoreclose to ensure that
the breaker can perform a trip-close-trip cycle.
•
A typical 11/33kV reclaim time is 3 - 10 seconds; this prevents unnecessary lockout
during thunderstorms. However, reclaim times up to 60 - 180 seconds maybe used.
4.2.11 Fuse application
An application of the ARC is the coordination with a fuse. This application is typical in rural
areas where derived lines are protected by a fuse.
We suppose to have the following settings for the protection and the ARC narrow to the
configuration matrix. All the others have to be compliance with the rules above.
67 protection
I> ON I>> ON
I> 8 In I>> 10 In
tI> 5 sec. tI>> 0 sec
AUTORECLOSE
(only the matrix)
ARC cycles
AR init tI> 4 3 2 1
0 1 1 0
ARC cycles
AR init tI>> 4 3 2 1
0 0 2 1
ARC cycles
AR init tI>>> 4 3 2 1
0 0 0 0
ARC cycles
AR init tAux1 4 3 2 1
0 0 0 0
Number of phase
cycles 1