Siemens SIPROTEC 7SS52, Руководство по эксплуатации

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4 - 28
Siemens AG
⋅
May 1998
When the circuit breaker auxiliary contact (auxiliary
contact closed when circuit breaker is open) is
connected, then the 7SS52 can react depending
on the status of the circuit breaker. When the cirĆ
cuit breaker is open, then the coupler current
I
CPBBA
is set to zero (digitized currents to 0) and
the polarity is reversed for I
CPBBB
(unbalancing by
changing the signs of the digitized currents). Thus,
DI
BBB
= twice the sum of the currents in feeders
on BBB and DI
BBA
= 0.
3. If the bus coupler is equipped with 2 current transĆ
formers, so that the bus zones are overlapping
(see Fig 4.27), then the digitized currents of the
bus coupler are set to zero when the circuit-breaĆ
ker is open.
BBA
BBB
2
1
CPBBA
= 0
CPBBB
= 0
Figure 4.27 Bus coupler with 2 CT's (overlapping measurement)
In this case, BBB is correctly cleared and BBA reĆ
mains in service.
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In order to detect a short-circuit between current
transformer and circuit breaker correctly, the circuit
breaker status must be known. ( $ ).
If the bus coupler circuit breaker is open, then the
current of the coupler bay is unbalanced for the proĆ
tection of busbar BBB and set to 0 for the protection
of busbar BBA (figure 4.28)
This might eventually cause tripping of the healthy
bus zone BBA when closing the bus coupler circuit
breaker onto a short-circuit on bus zone BBB, beĆ
cause the protection criterion is faster than the circuit
breaker status processing. To avoid this, a leading
contact for closing the circuit breaker integrates the
current of the coupler current transformer into the
protection algorithm.
The designer has to select a suitable "leading conĆ
tact".
Depending on the application, the leading recognition
of the close command has to be ensured for manual
closing control, eventual remote control of the bus
coupler circuit breaker by telecontrol or substation
control systems and also reclosing by an automatic
reclosing device.
BBA
BBB
Figure 4.28 Switching onto earthed busbar
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The OPEN status of the bus coupler circuit breaker is
essential for correct reaction in case of faults in the
dead zone, too ( $ ). If the circuit breaker
(CB) is open, then
1. in case of one coupler current transformer, the
coupler current of the current transformer allocaĆ
ted to the bus zone is inverted and the second is
set to zero
2. in case of two coupler current transformers, both
currents are set to zero.
In order to avoid that, after a bus fault, the breaker
failure protection is undercut when the circuit breaker
reaches its final position, so that eventually a healthy
busbar is jeopardized by current transformer remaĆ
ence, the signal CB-OPEN is processed time-deĆ
layed.
The specific processing of the coupler bay currents
starts only after the set time delay "T-CB-OPEN"
( ) has elapsed
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