ABB RED650 Applications Manual page 237

1MRK 505 393-UEN B
Line differential protection RED650 2.2 IEC
Application manual
To maximize the availability of the power system it is possible to choose single-
phase tripping and automatic reclosing during single-phase faults and three-phase
tripping and automatic reclosing during multi-phase faults. Three-phase automatic
reclosing can be performed with or without the use of synchrocheck.
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 (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
Section 12
Control
231