Setting Notes - Siemens Siprotec 7VK61 Manual

Functions
2.6 Circuit breaker failure protection (optional)
2.6.2

Setting Notes

General
The circuit breaker failure protection and its ancillary functions (end fault protection, pole discrepancy supervi-
sion) can only operate if they were set during configuration of the scope of functions (address 139 BREAKER
FAILURE, setting Enabled or enabled w/ 3I0>).
Breaker failure protection
The breaker failure protection is switched ON or OFF at address 3901 FCT BreakerFail.
The current threshold I> BF (address 3902) should be selected such that the protection will operate with the
smallest expected short-circuit current. A setting of 10 % below the minimum fault current for which breaker
failure protection must operate is recommended. On the other hand, the value should not be set lower than
necessary.
If the breaker failure is configured with zero sequence current threshold (address 139 = enabled w/ 3I0>),
the pickup threshold for the zero sequence current 3I0> BF (address 3912) can be set independently of I>
BF.
Normally, the breaker failure protection evaluates the current flow criterion as well as the position of the breaker
auxiliary contact(s). If the auxiliary contact(s) status is not available in the device, this criterion cannot be pro-
cessed. In this case, set address 3909 Chk BRK CONTACT to NO.
Two-stage Breaker Failure Protection
With two-stage operation, the trip command is repeated after a time delay T1 to the local feeder breaker, nor-
mally to a different set of trip coils of this breaker. A choice can be made whether this trip repetition shall be
single-pole or three-pole if the initial feeder protection trip was single-pole (provided that single-pole trip is pos-
sible). This choice is made in address 3903 1p-RETRIP (T1). Set this parameter to YES if the first stage is
to trip single-pole, otherwise set it to NO.
If the breaker does not respond to this trip repetition, the adjacent circuit breakers are tripped after T2, i.e. the
circuit breakers of the busbar or of the concerned busbar section and, if necessary, also the circuit breaker at
the remote end unless the fault has been cleared.
Separate delay times can be set
• for single- or three-pole trip repetition to the local feeder circuit breaker after a 1-pole trip of the feeder pro-
tection T1-1pole at address 3904,
• for three-pole trip repetition to the local feeder circuit breaker after 3-pole trip of the feeder protection T1-
3pole (address 3905),
• for trip of the adjacent circuit breakers (busbar zone and remote end if applicable) T2 at address 3906.
Note
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.
Therefore, you should set T1-1pole equal to or longer than T1-3pole.
The delay times are set dependant on the maximum operating time of the feeder circuit breaker and the reset
time of the current detectors of the breaker failure protection, plus a safety margin which allows for any toler-
ance of the delay timers. Figure 2-43 illustrates the timing of a typical breaker failure scenario. The dropout time
for sinusoidal currents is ≤ 15 ms. If current transformer saturation is anticipated, the time should be set to
25 ms.
126
SIPROTEC, 7VK61, Manual
C53000-G1176-C159-3, Release date 05.2009