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:
_
2 1³ + + +
cbopen BFP reset margin
t t t t t
EQUATION1430 V1 EN-US (Equation 34)
where:
t
cbopen
is the maximum opening time for the circuit breaker
t
BFP_reset
is the maximum time for breaker failure protection to detect correct breaker function (the
current criteria reset)
t
margin
is a safety 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.
1MRK 504 169-UEN A Section 7
Current protection
Transformer protection RET650 2.2 IEC 139
Application manual
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