During the single-phase dead time there is an equivalent "series"-fault in the system
resulting in a flow of zero sequence current. It is therefore necessary to coordinate the
residual current protections (ground fault protection) with the single-phase tripping and
the auto reclosing function. Attention shall also be paid to “pole discrepancy” that
arises when circuit breakers are provided with single-phase operating devices. These
breakers need pole discrepancy protection. They must also be coordinated with the
single-phase 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 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 breaker-
and-a-half, 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.
Section 12
1MRK 505 370-UUS A
Control
316
Busbar protection REB670 2.2 ANSI
Application manual
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