ABB Relion 670 Series Applications Manual page 185

1MRK 511 401-UEN Rev. K
accordance with the most sensitive protection function to start the breaker failure protection.
Default setting is 10% of
where Ir is rated current of the IED CT input where the function is connected. In principle Ir is
either 1A or 5A depending on the ordered IED.
I>BlkCBPos : If the FunctionMode is set to Current or CB pos breaker failure for high current
faults are safely detected by the current measurement function. To increase security for low
currents the contact based function will be enabled only if the current at the moment of
starting is below this set level. The setting can be given within the range 5 – 200% of
is strongly recommended to set this level above IPh> set level.
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-to-earth faults in
such systems it is necessary to measure the residual current separately. The
be set 1 out of 4 in such systems 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
t1 : Time delay of the retrip. The setting can be given within the range 0 – 60s in steps of 0.001
s. Typical setting is within range 0 – 50ms.
t2 : Time delay of the backup 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 within range 90 – 200ms
(also dependent of retrip timer).
t2 is used when function is started in one phase only (i.e. for single-phase to ground
Timer
fault on an OHL (Over Head Lines) when single-pole auto-reclosing is used).
The minimum time delay for the backup trip can be estimated as:
 
t2 t1 t
IECEQUATION18191 V1 EN-US
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.
Bay control REC670
Application manual
IBase . Note that this setting shall not be set lower than 4% of Ir,
IBase .
 
t t
margin
CB_open BFP_reset
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
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Section 8
Current protection
IBase . It
BuTripMode shall
(Equation 67)
179