ABB REC670 Applications Manual page 309

1MRK 511 401-UEN A
Bay control REC670 2.2 IEC
Application manual
coordinate the residual current protections (earth fault protection) with the single-
phase tripping and the auto reclosing function. Attention shall also be paid to "pole
discordance" that arises when circuit breakers are provided with single-phase
operating devices. These breakers need pole discordance protection. They must
also be coordinated with the single-phase auto recloser and blocked during the dead
time when a normal discordance 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
dead 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
dead 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- recloser per line end. If
auto reclosers are included in duplicated line protection, which means two auto
reclosers 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 recloser per CB is recommended. Arranged in
such a way, that sequential reclosing of the two CBs can be arranged with a priority
circuit available in the auto recloser. 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.
The auto recloser can be selected to perform single-phase and/or three-phase
automatic reclosing from several single-shot to multiple-shot reclosing programs.
The three-phase auto reclosing dead time can be set to give either High-Speed
Automatic Reclosing (HSAR) or Delayed Automatic Reclosing (DAR). These
expressions, HSAR and DAR, are mostly used for three-phase auto reclosing as
single-phase auto reclosing is always high speed to avoid maintaining the
unsymmetrical condition. HSAR usually means a dead time of less than 1 second.
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 automatic
reclosing 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 recloser can be inhibited
(blocked) when certain protection functions detecting permanent faults, such as
shunt reactor, cable or busbar protection are in operation. Back-up protection zones
Section 14
Control
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