Hitachi Relion 670 Series Applications Manual page 176

Section 8
Current protection
Table 23:
RetripMode
Retrip Off
CB Pos Check
No CBPos Check
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
IBase.
I>BlkCont: If contact based detection for breaker failure is used, this feature can be blocked if any
phase current is larger than this setting level. If the 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 measurement should be enabled only for small currents. The setting can
be given within the range 5 – 200% of IBase.
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).
Timer t2 is used when function is started in one phase only (i.e. for single-phase to ground 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.
170
Dependencies between parameters RetripMode and FunctionMode
FunctionMode
N/A
Current
Contact
Current/Contact
Current
Contact
Current/Contact
 
t t
CB_open BFP_reset margin
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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1MRK506375-UEN Rev. N
Description
The retrip function is not activated
retrip is done if the phase current is
larger than the operate level after
retrip time has elapsed
retrip is done when auxiliary contact
position indicates that breaker is still
closed after retrip time has elapsed
Both methods according to above are
used but taken into account also
I>BlkCont
retrip is done without check of current
level
retrip is done without check of
auxiliary contact position
retrip is done without check of current
level or auxiliary contact position
(Equation 58)
Railway application RER670
Application manual