value of 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 151)
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 424: 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
The retrip logic provides the
TRRET
output, which can be used to give a retrip signal
for the main circuit breaker. Timer 1 activates the retrip logic. The operation of the
retrip logic depends on the
CB fail retrip mode setting.
1MRS757644 H
Protection related functions
620 series
Technical Manual
809
