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Functions
2.6 Circuit breaker failure protection (optional)
Delay times
When the initiate conditions are fulfilled, the associated timers are started. The circuit breaker pole(s) must
open before the associated time has elapsed.
Different delay times are possible for single-pole and three-pole initiation. An additional delay time can be used
for two-stage breaker failure protection.
With single-stage breaker failure protection, the trip command is routed to the adjacent circuit breakers which
then interrupt the fault current if the local feeder breaker fails (Figure 2-27 or Figure 2-28). Adjacent circuit
breakers are the ones of the busbar or busbar section to which the considered feeder is connected. The pos-
sible initiation conditions for the breaker failure protection are those discussed above. Depending on the appli-
cation of the feeder protection, common phase or phase-segregated initiation conditions may occur. The trip-
ping by the breaker failure protection is always three-pole.
The simplest solution is to start the delay timer T2 (Figure 2-36). The phase-segregated initiation signals are
omitted if the feeder protection always trips three-pole or if the circuit breaker is not capable of single-pole trip-
ping.
If it is desired to use shorter delay times for 3-pole tripping of the starting protection function than for single-
pole tripping, you should use the delay times T1-3pole and T1-1pole as shown in Figure 2-37.
Figure 2-36
Figure 2-37
With two-stage breaker failure protection the trip command of the feeder protection is usually repeated, after a
first time stage, to the feeder circuit breaker, often via a second trip coil or set of trip coils, if the breaker has not
responded to the original trip command. A second time stage monitors the response to this repeated trip
command and trips the breakers of the relevant busbar section if the fault has not yet been cleared after this
second time.
For the first stage, the time delay T1-1pole can be set for single-pole tripping by the starting protection func-
tion which is longer than for three-pole tripping. Moreover, you can specify (by setting parameter 1p-RETRIP
(T1)) whether the breaker failure protection trips single-pole or always 3-pole after the first stage has expired.
In case of multi-phase tripping of the feeder protection, T1-1pole and T1-3pole are started in parallel. T1-
3pole therefore allows accelerating the tripping of the breaker failure protection compared to T1-1pole
122
Single-stage breaker failure protection with common phase initiation
Single-stage breaker failure protection with different delay times
SIPROTEC, 7VK61, Manual
C53000-G1176-C159-3, Release date 05.2009
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