P54x/EN OP/La4 Operation
(OP) 5-150
MiCOM P543, P544, P545 & P546
OP
&
DDB Pole Discrepancy (451)
1
INTSIG ARLockout (effectively DDB_CB_Lockout_Alarm (860)
1
DDB CB Open A ph (904)
DDB CB Open B ph (905)
DDB CB Open C ph (906)
&
DDB Pole Discrepancy (699)
P1106ENf
Figure 98 Ddb pole discrepancy trip (P543/P545)
4.2 System checks (including check sy
nchronizer) (P543/P545)
4.2.1 Overview (P5
43/P545)
In some situations it is possible for both “bus” and “line” sides of a circuit breaker to be live
when the circuit breaker is open, for example at the ends of a feeder which has a power
source at each end. Therefore, when closing the circuit breaker, it is normally necessary to
check that the network conditions on both sides are suitable, before giving a CB Close
command. This applies to both manual circuit breaker closing and auto-reclosure. If a
circuit breaker is closed when the line and bus voltages are both live, with a large phase
angle, frequency or magnitude difference between them, the system could be subjected to
an unacceptable shock, resulting in loss of stability, and possible damage to connected
machines.
System checks involve monitoring the voltages on both sides of a circuit breaker, and, if both
sides are live, performing a synchronism check to determine whether the phase angle,
frequency and voltage magnitude differences between the voltage vectors, are within
permitted limits.
The pre-closing system conditions for a given circuit breaker depend on the system
configuration and, for auto-reclosing, on the selected auto-reclose program. For example,
on a feeder with delayed auto-reclosing, the circuit breakers at the two line ends are
normally arranged to close at different times. The first line end to close usually has a live
bus and a dead line immediately before reclosing, and charges the line (dead line charge)
when the circuit breaker closes. The second line end circuit breaker sees live bus and live
line after the first circuit breaker has reclosed. If there is a parallel connection between the
ends of the tripped feeder, they are unlikely to go out of synchronism, i.e. the frequencies will
be the same, but the increased impedance could cause the phase angle between the two
voltages to increase. Therefore the second circuit breaker to close might need a
synchronism check, to ensure that the phase angle has not increased to a level which would
cause unacceptable shock to the system when the circuit breaker closes.
If there are no parallel interconnections between the ends of the tripped feeder, the two
systems could lose synchronism, and the frequency at one end could “slip” relative to the
other end. In this situation, the second line end would require a synchronism check
comprising both phase angle and slip frequency checks.
If the second line end busbar has no power source other than the feeder which has tripped,
the circuit breaker will see a live line and dead bus assuming the first circuit breaker has
reclosed. When the second line end circuit breaker closes the bus will charge from the live
line (dead bus charge).
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