Section 4 1MAC309294-MB F
Protection functions
240 RER620
Technical Manual
Timer 2
Once activated, the timer runs until the set CB failure delay value is elapsed. The time
characteristic is according to DT. When the operation timer has reached the set maximum
time value CB failure delay, the TRBU output is activated. The 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 retrip can be estimated as:
t
cbopen
maximum opening time for the circuit breaker
t
BFP_reset
is the 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 is often dependent on the ability to maintain transient stability in case of a fault close
to a power plant.
Figure 111: Time line of 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 is elapsed. The time characteristic is according to DT. When the
operation timer has reached the maximum time value, the CB_FAULT_AL output is
activated. After the set time an alarm is given so that actions can be done to repair the
circuit breaker. A typical value is 5 s.
CBfailuredelay Retriptime t t t
cbopen BFP reset margin
≥+++
_
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