ABB REL650 Applications Manual page 325

1MRK 506 334-UUS A
Application manual
that each phase breaker operates individually, which is usually the case for higher
transmission voltages.
A somewhat longer dead time may be required for single-phase reclosing compared to
high-speed three-phase reclosing. This is due to the influence on the fault arc from the
voltage and the current in the non-tripped phases.
To maximize the availability of the power system it is possible to choose single pole
tripping and automatic reclosing during single-phase faults and three pole tripping and
automatic reclosing during multi-phase faults. Three-phase automatic reclosing can be
performed with or without the use of a synchronism check, and an energizing check, such
as dead line or dead busbar check.
During the single-pole open 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 pole tripping and the
auto-reclosing function. Attention shall also be paid to "pole discordance" (pole
discordance) that arises when circuit breakers are provided with single pole operating
devices. These breakers need pole discordance protection. They must also be coordinated
with the single pole 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 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 breaker-and-a-half, 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.
Section 11
Control
319