Tau
: The thermal time constant of the protected circuit given in minutes. Please
refer to equipment manufacturer manuals for details.
TripTemp
: Temperature value for trip of the protected circuit. For cables, a
maximum allowed conductor temperature is often stated to be 90°C. For overhead
lines, the critical temperature for aluminium conductor is about 90 - 100°C.
However, for railway catenary lines, the critical temperature can be as low as 48°C.
For a copper conductor a normal figure is 70°C. For power transformers, it depends
on the application and used type of paper insulation. Some typical value is around
100°C.
AlarmTemp
: Temperature level for alarm of the protected circuit. ALARM signal
can be used as a warning before the circuit is tripped. Therefore the setting shall be
lower than the trip level. It shall at the same time be higher than the maximum
conductor temperature at normal operation. A suitable setting can be about 15°C
below the trip value.
ReclTemp
: Temperature where lockout signal LOCKOUT from the protection is
released. When the thermal overload protection trips, a lock-out signal is activated.
This signal is intended to block switch in of the protected circuit as long as the
conductor temperature is high. The signal is released when the estimated
temperature is below the set value. This temperature value should be chosen below
the alarm temperature.
8.7
Breaker failure protection CCRWRBRF
IP14514-1 v6
8.7.1
Application
M13916-3 v7
In the design of the fault clearance system the N-1 criterion is often used. This
means that a fault needs to be cleared even if any component in the fault clearance
system is faulty. One necessary component in the fault clearance system is the
circuit breaker. It is from practical and economical reason not feasible to duplicate
the circuit breaker for the protected object. Instead a breaker failure protection is
used.
Breaker failure protection (CCRWRBRF) will issue a back-up trip command to the
adjacent circuit breakers in case of failure to trip of the “normal” circuit breaker for
the protected object. The detection of failure to break the current through the
breaker is made by means of either current measurement or status of CB axillary
contact.
CCRWRBRF can also give a re-trip. This means that a separate trip signal is sent to
the protected circuit breaker first. The re-trip function can be used to increase the
probability of operation of the breaker, or it can be used to avoid back-up trip of
many breakers in case of mistakes during relay maintenance and testing.
1MRK 506 375-UEN A
Section 8
Current protection
Railway application RER670 2.2 IEC
187
Application manual
Summary of Contents for RELION RER670
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