ABB REQ650 Applications Manual page 219

1MRK 505 291-UEN A
Application manual
residual current protections (earth fault protection) with the single pole tripping and
the auto-reclosing function. Attention shall also be paid to "pole discrepancy" (pole
discordance) that arises when circuit breakers are provided with single pole operating
devices. These breakers need pole discrepancy protection. They must also be
coordinated with the single pole auto-recloser and blocked during the dead time when
a normal discrepancy occurs. Alternatively they should use a trip time longer than the
set single phase dead time.
For the individual line breakers and auto-reclosing equipment, the "auto-reclosing
open time" expression is used. This is the dead time setting for the Auto-Recloser.
During simultaneous tripping and reclosing at the two line ends, auto-reclosing open
time is approximately equal to the line dead time. Otherwise these two times may
differ as one line end might have a slower trip than the other end which means that the
line will not be dead until both ends have opened.
If the fault is permanent, the line protection will trip again when reclosing is attempted
in order to clear the fault.
It is common to use one automatic reclosing function per line circuit-breaker (CB).
When one CB per line end is used, then there is one auto-reclosing function per line
end. If auto-reclosing functions are included in duplicated line protection, which
means two auto-reclosing functions per CB, one should take measures to avoid
uncoordinated reclosing commands. In 1 1/2 breaker, double-breaker and ring bus
arrangements, two CBs per line end are operated. One auto-reclosing function per CB
is recommended. Arranged in such a way, sequential reclosing of the two CBs can be
arranged with a priority circuit available in the auto-reclose function. In case of a
permanent fault and unsuccessful reclosing of the first CB, reclosing of the second CB
is cancelled and thus the stress on the power system is limited. Another advantage with
the breaker connected auto-recloser is that checking that the breaker closed before the
sequence, breaker prepared for an autoreclose sequence and so on is much simpler.
The auto-reclosing function can be selected to perform single-phase and/or three
phase automatic-reclosing from several single-shot to multiple-shot reclosing
programs.
In power transmission systems it is common practice to apply single and/or three
phase, single-shot Auto-Reclosing. In Sub-transmission and Distribution systems
tripping and auto-reclosing are usually three-phase. The mode of automaticreclosing
varies however. Single-shot and multi-shot are in use. The first shot can have a short
delay, HSAR, or a longer delay, DAR. The second and following reclosing shots have
a rather long delay. When multiple shots are used the dead time must harmonize with
the breaker duty-cycle capacity.
Automatic-reclosing is usually started by the line protection and in particular by
instantaneous tripping of such protection. The auto-reclosing function can be
inhibited (blocked) when certain protection functions detecting permanent faults,
such as shunt reactor, cable or bus bar protection are in operation. Back-up protection
zones indicating faults outside the own line are also connected to inhibit the Auto-
Reclose.
Section 10
Control
213