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Section 7
Current protection
Table 34: Dependencies between RetripMode and FunctionMode
RetripMode
Off
UseFunctionMode
Always
IP> : Current level for detection of breaker failure, set in % of IBase . This parameter should be
set so that faults with small fault current can be detected. The setting can be chosen in
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 function is connected. In principle Ir is
either 1A or 5A depending on the ordered IED
I>BlkCont : 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
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 90 – 200ms (also
dependent of retrip timer).
The minimum time delay for the backup trip can be estimated as:
t
2
t
1
EQUATION1430 V2 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 to maintain transient stability in case of a fault
close to a power plant.
186
IBase . Note that this setting shall not be set lower than 4% of Ir,
t
t
t
CB open
_
BFP reset
_
m
arg
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
FunctionMode
N/A
Current
CB Pos
Current or CB Pos
N/A
IPh> set level.
in
1MRK 505 370-UEN D
Description
the re-trip function is disabled
a phase current must be larger
than the set operate level to allow
re-trip once the t1 timer elapses
Re-trip is done when breaker
position indicates that breaker is
still closed after re-trip time has
elapsed
both methods are used
Re-trip is always given when t1
elapses without any further
checks
IBase . It
(Equation 42)
Busbar protection REB670
Application manual
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