ABB Relion 670 Series Applications Manual page 194

Section 7
Current protection
where:
t
CB_open
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 of the power system 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 104: Time sequence
t2MPh: Time delay of the backup 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 backup trip delay for multi-phase faults. Typical setting is 90 – 150 ms.
Note that for a protected object which are always tripped three-phase (e.g. transformers, generators,
reactors, cables, etc.) this timer shall always be set to the same value as t2 timer.
t3: Additional time delay to t2 for a second backup trip TRBU2. In some applications there might be a
requirement to have separated backup trip functions, tripping different backup 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. Note that the time delay for backup trip t2 is bypassed when the 52FAIL is active.
Typical setting is 2.0 seconds..
188
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)
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after re-trip
t
BFPreset
Margin
1MRK 505 370-UUS Rev. K
Time
ANSI05000479_3_en.vsd
Busbar protection REB670
Application manual