'(& )( )'& &) ( &!& ")& &$(( $# Ć %&( $# #)" &&#$
4 - 20
Siemens AG ⋅ May 1998
After the TRIP repetition time has elapĆ
sed and if the release criterion is fulfilled, the related
bay unit issues a phase-selective or three-phase
TRIP command.
The condition for a single-phase TRIP repetition is
that both the feeder current in the CBF-initiating
phase and the earth current exceed the threshold
> CBF (Lx & E). Here the parameter TRIP-R-OP:
( ) must be set to "single-phase". For
three-phase TRIP repetition, the parameter (
) must be set to "three-phase".
In addition at least 2 currents must exceed the curĆ
rent treshold for two-phase or three-phase CBF-inĆ
itiation [(Lx & Ly)v(Lx & E)].
If the circuit breaker trips correctly, then the CBF inĆ
itiation resets and there will be no zone-selective
TRIP command.
If the CBF initiation persists, then the time delay of
the CBF ( ) elapses. In conformity with
the actual isolator replica, all feeders are tripped,
which are allocated to the bus section of the CBF inĆ
itiating bay unit.
A further condition is that the current threshold (
), which can be set individually for each feeĆ
der, is exceeded during the total time period
"T-CBF".
If the current falls below the threshold, then the runĆ
ning time T-CBF is interrupted.
This operation mode yields three essential advantaĆ
ges:
D Full protection stability, similar to the busbar proĆ
tection measurement, is maintained
D No special demands are made on the reset time of
the feeder protection; i.e. even with a longer reset
time, there is no danger of false tripping since the
circuit-breaker has interrupted the current and a
differential current is not formed by the unbalancĆ
ing.
D The circuit-breaker failure protection has its own
set of parameter settings for differential current
limit and stabilizing factor setting independent of
busbar protection. The feeder-selective matching
of the differential current limit is obtained by multiĆ
plication of the differential current limit by the acĆ
tual CT ratio. This enables circuit-breaker failure
detection even with low-current short-circuits.
three-phase
TRIP command
P
t
1
T-CBF
(zone-selective)
L-kx ȧāȧ >0
transfer trip
command
(feeder-selective)
P 1/2-channel
BI suĆ
pervision
1
unbalancing
Lx
&
(figure 4.32,
chapter 4.7.8.5)
P
>CBF Ayy
trip criteĆ
rion fulfilĆ
led?
(Lx & Ly) v
(Lx &
E
)
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