The minimum time delay for the retrip can be estimated as:
CBfailuredelay Retriptime t t t
cbopen BFP reset margin
≥ + + +
_
A070693 V3 EN (Equation 75)
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.
GUID-1A2C47ED-0DCF-4225-9294-2AEC97C14D5E V1 EN
Figure 287: 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
1YHT530004D05 D Section 5
Protection related functions
615 series 545
Technical Manual
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