ABB REB670 Applications Manual page 214

Section 7
Current protection
208
It is often required that the total fault clearance time shall be less than a given critical time.
This time is often dependent of the ability to maintain transient stability in case of a fault
close to a power plant.
Protection
operate time
Normal t
The fault Retrip delay t1
occurs
Trip and Pickup
CCRBRF
(50BF)
ANSI05000479 V3 EN
Figure 91: Time sequence
t3: Additional time delay to t2 for a second back-up trip TRBU2. In some applications
there might be a requirement to have separated back-up trip functions, tripping different
back-up circuit breakers.
tCBAlarm: Time delay for alarm in case of indication of faulty circuit breaker. There is a
binary input 52FAIL from the circuit breaker. This signal is activated when internal
supervision in the circuit breaker detect that the circuit breaker is unable to clear fault. This
could be the case when gas pressure is low in a SF6 circuit breaker, of others. After the set
time an alarm is given, so that actions can be done to repair the circuit breaker. The time
delay for back-up trip is bypassed when the 52FAIL is active. Typical setting is 2.0
seconds.
tPulse: Trip pulse duration. This setting must be larger than the critical impulse time of
circuit breakers to be tripped from the breaker failure protection. Typical setting is 200 ms.
cbopen
t after re-trip
cbopen
t
BFPreset
Minimum back-up trip delay t2
Critical fault clearance time for stability
1MRK 505 337-UUS -
Margin
Time
ANSI05000479_3_en.vsd
Application manual