this setting is made as low as possible at the same time as any unwanted operation
is avoided. A typical setting is 90 - 150 ms, which is also dependent on the retrip
timer.
The minimum time delay for the CB failure delay can be estimated as:
CBfailuredelay Retriptime t t t
cbopen BFP reset margin
≥ + + +
_
(Equation 291)
t
cbopen
Maximum opening time for the circuit breaker
t
BFP_reset
Maximum time for the breaker failure protection to detect the correct breaker
function (the current criteria reset)
t
margin
Safety margin
It is often required that the total fault clearance time is less than the given critical
time. This time often depends on the ability to maintain transient stability in case of
a fault close to a power plant.
Figure 662: Timeline of the breaker failure protection
Timer 3
This module is activated by the CB_FAULT signal. Once activated, the timer runs
until the set
CB fault delay
value has elapsed. The time characteristic is according to
DT. When the operation timer has reached the maximum time value
CB fault delay
,
the CB_FAULT_AL output is activated. After the set time, an alarm is given so that
the circuit breaker can be repaired. A typical value is 5 s.
Retrip logic
Timer 1 activates Retrip logic, which can be used to give a retrip signal TRRET for
the main circuit breaker. The operation of Retrip logic depends on the settings
CB
failure mode
and
CB fail retrip mode
as shown in
Table 1114
.
1MRS759142 F
Protection related functions
REX640
Technical Manual
1167
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