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.
Time
The fault
occurs
Protection
operate time
Trip and Pickup
CCRBRF
(50BF)
Normal t
cbopen
Margin
Retrip delay t1 t
cbopen
after re-trip
t
BFPreset
Minimum back-up trip delay t2
Critical fault clearance time for stability
ANSI05000479_3_en.vsd
ANSI05000479 V3 EN
Figure 280: Time sequence
t2MPh: Time delay of the back-up trip at multi-phase initiate. The critical fault clearance
time is often shorter in case of multi-phase faults, compared to single phase-to-ground
faults. Therefore there is a possibility to reduce the back-up trip delay for multi-phase
faults. Typical setting is 90 – 150 ms.
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. 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.
1MRK 506 369-UUS - Section 9
Current protection
Line distance protection REL670 2.2 ANSI 543
Application manual
To Next Page
Loading...
