ABB RELION 670 Series Applications Manual page 189

1MRK 505 337-UUS A
where:
t
cbopen
t
BFP_reset
t
margin
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
The fault
occurs
ANSI05000479 V3 EN-US
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.
Application manual
is the maximum opening time for the circuit breaker
is the maximum time for breaker failure protection to detect correct breaker function
(the current criteria reset)
is a safety margin
Normal t
cbopen
Retrip delay t1 t
cbopen
Minimum back-up trip delay t2
Critical fault clearance time for stability
Trip and Pickup
CCRBRF
(50BF)
after re-trip
t
BFPreset
Margin
Current protection
Time
ANSI05000479_3_en.vsd
Section 7
183