Application - ABB REF615 Applications Manual

1MRS756378 D
6.2.3
REF615
Application Manual
external commands through binary inputs. The start command is always a default for
three-phase operation. CCBRBRF includes a three-phase conditional or
unconditional re-trip function, and also a three-phase conditional back-up trip
function.
CCBRBRF uses the same levels of current detection for both re-trip and back-up trip.
The operating values of the current measuring elements can be set within a predefined
setting range. The function has two independent timers for trip purposes: a re-trip
timer for the repeated tripping of its own breaker and a back-up timer for the trip logic
operation for upstream breakers. A minimum trip pulse length can be set
independently for the trip output.
The function contains a blocking functionality. It is possible to block the function
outputs, if desired.

Application

The n-1 criterion is often used in the design of a fault clearance system. This means
that the fault is cleared even if some component in the fault clearance system is faulty.
A circuit breaker is a necessary component in the fault clearance system. For practical
and economical reasons, it is not feasible to duplicate the circuit breaker for the
protected component, but breaker failure protection is used instead.
The breaker failure function issues a back-up trip command to adjacent circuit
breakers in case the original circuit breaker fails to trip for the protected component.
The detection of a failure to break the current through the breaker is made by
measuring the current or by detecting the remaining trip signal (unconditional).
CCBRBRF can also retrip. This means that a second trip signal is sent to the protected
circuit breaker. The retrip function is used to increase the operational reliability of
the breaker. The function can also be used to avoid back-up tripping of several
breakers in case mistakes occur during relay maintenance and tests.
CCBRBRF is initiated by operating different protection functions or digital logics
inside the IED. It is also possible to initiate the function externally through a binary
input.
CCBRBRF can be blocked by using an internally assigned signal or an external signal
from a binary input. This signal blocks the function of the breaker failure protection
even when the timers have started or the timers are reset.
The retrip timer is initiated after the start input is set to true. When the pre-defined
time setting is exceeded, CCBRBRF issues the retrip and sends a trip command, for
example, to the circuit breaker's second trip coil. Both a retrip with current check and
an unconditional retrip are available. When a retrip with current check is chosen, the
retrip is performed only if there is a current flow through the circuit breaker.
The back-up trip timer is also initiated at the same time as the retrip timer. If
CCBRBRF detects a failure in tripping the fault within the set back-up delay time,
which is longer than the retrip time, it sends a back-up trip signal to the chosen back-
Protection related functions
Section 6
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