ABB REC670 Applications Manual page 203

1MRK 511 401-UEN A
Bay control REC670 2.2 IEC
Application manual
FunctionMode is set Current/Contact breaker failure for high current faults are
safely detected by the current measurement function. To increase security the
contact based function should be disabled for high currents. The setting can be
given within the range 5 – 200% of IBase.
IN>: Residual current level for detection of breaker failure set in % of IBase. In
high impedance earthed systems the residual current at phase- to-earth faults are
normally much smaller than the short circuit currents. In order to detect breaker
failure at single-phase-earth faults in these systems it is necessary to measure the
residual current separately. Also in effectively earthed systems the setting of the
earth-fault current protection can be chosen to relatively low current level. The
BuTripMode is set 1 out of 4. The current setting should be chosen in accordance to
the setting of the sensitive earth-fault protection. The setting can be given within
the range 2 – 200 % of IBase.
t1: Time delay of the re-trip. The setting can be given within the range 0 – 60s in
steps of 0.001 s. Typical setting is 0 – 50ms.
t2: Time delay of the back-up trip. The choice of this setting is made as short as
possible at the same time as unwanted operation must be avoided. Typical setting is
90 – 200ms (also dependent of re-trip timer).
The minimum time delay for the re-trip can be estimated as:
³ + +
t 2 t 1 t t
cbopen BFP reset _
EQUATION1430 V1 EN-US
where:
t is the maximum opening time for the circuit breaker
cbopen
t is the maximum time for breaker failure protection to detect correct breaker function (the
BFP_reset
current criteria reset)
t is a safety margin
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.
+
t
margin
Section 8
Current protection
(Equation 62)
197