3.1.8 Calculating settings for breaker failure protection 3-phase
activation and output CCRBRF
Breaker failure protection, 3-phase activation and output can use either contact
function in the circuit breaker or current measurement to detect correct breaker
function. Current measurement breaker check seems to be the most suitable function
for line protection.
1. Set GlobalBaseSel to 1
The settings are made in primary values. These values are given in the base
settings in Global base 1.
2. Set FunctionMode to Current
3. Set BuTripMode to 1 out of 4
In the current measurement, three-phase current on the line is used. It is also
possible to measure the residual current (analogue input 4). The logic to detect
circuit breaker failure can be chosen:
1 out of 3: at least one of the three-phase currents shall be higher than the set level
to detect failure to break
1 out of 4: at least one of the three-phase currents and the residual current shall
be higher than the set level to detect failure to break
2 out of 4: at least two of the three-phase currents and the residual current shall
be higher than the set level to detect failure to break
As the residual current protection is one of the protection functions to initiate the
breaker failure protection, the setting 1 out of 4 is chosen.
4. Set IP> to 50 % of the base current.
IP> should be set lower than the lowest current to be detected by the phase
overcurrent protection which is about 800 A.
5. Set IN> to 10 % of the base current.
IN> should be set lower than the lowest current to be detected by the busbar
protection which is about 100 A.
6. Set the re-tip time delay t1 to 0
The delay time of the breaker failure protection (BuTrip) is chosen according to
figure
21.
• The maximum open time of the circuit breaker is considered to be 100 ms.
• The CCRBRF reset time is max 15 ms.
• The margin should be chosen to about 2 cycles.
This results in about 155 ms minimum setting of backup trip delay t2.
Section 3 1MRK 505 291-UEN A
REQ650 setting examples
58
Application manual
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