Timer 1
Once activated, the timer runs until the set Retrip time value has elapsed. The time
characteristic is according to DT. When the operation timer has reached the value set with
Retrip time, the retrip logic is activated. A typical setting is 0...50 ms.
Timer 2
Once activated, the timer runs until the set CB failure delay value has elapsed. The time
characteristic is according to DT. When the operation timer has reached the set maximum
time value CB failure delay, the backup trip logic 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 CB failure delay can be estimated as:
CBfailuredelay Retriptime t t t
cbopen BFP reset margin
≥ + + +
_
A070693 V3 EN (Equation 136)
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.
Section 5 1MAC059074-MB A
Protection related functions
776 615 series ANSI
Technical Manual
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