GE C60 Instruction Manual page 438

GROUPED ELEMENTS
Initiation stage
A FlexLogic operand representing the protection trip signal initially sent to the breaker must be selected to initiate the
scheme. The initiating signal is sealed-in if primary fault detection can reset before the breaker failure timers have finished
timing. The seal-in is supervised by current level, so it is reset when the fault is cleared. If desired, an incomplete sequence
seal-in reset can be implemented by using the initiating operand to also initiate a FlexLogic timer, set longer than any
breaker failure timer, whose output operand is selected to block the breaker failure scheme.
For the C60 relay, the protection trip signal initially sent to the breaker is already programmed as a trip output. The
protection trip signal does not include other breaker commands that are not indicative of a fault in the protected
zone.
Schemes can be initiated either directly or with current level supervision. It is particularly important in any application to
decide if a current-supervised initiate is to be used. The use of a current-supervised initiate results in the breaker failure
element not being initiated for a breaker that has very little or no current flowing through it, which can be the case for
transformer faults. For those situations where it is required to maintain breaker fail coverage for fault levels below the
PH AMP SUPV PICKUP
those situations where coordinating margins can be reduced when high speed reclosing is used. Thus, if this choice is
made, fault levels must always be above the supervision pickup levels for dependable operation of the breaker fail scheme.
This can also occur in breaker-and-a-half or ring bus configurations where the first breaker closes into a fault; the
protection trips and attempts to initiate breaker failure for the second breaker, which is in the process of closing, but does
not yet have current flowing through it.
When the scheme is initiated, it sends a trip signal after a pickup delay to the breaker initially signaled to trip (this feature is
usually described as re-trip). This reduces the possibility of widespread tripping that results from a declaration of a failed
breaker.
5
Determination of a breaker failure condition
The schemes determine a breaker failure condition via three paths. Each of these paths is equipped with a time delay, after
which a failed breaker is declared and trip signals are sent to all breakers required to clear the zone. The delayed paths are
associated with breaker failure timers 1, 2, and 3, which are intended to have delays increasing with increasing timer
numbers. These delayed paths are individually enabled to allow for maximum flexibility.
Timer 1 logic (early path) is supervised by a fast-operating breaker auxiliary contact. If the breaker is still closed (as
indicated by the auxiliary contact) and fault current is detected after the delay interval, an output is issued. Operation of
the breaker auxiliary switch indicates that the breaker has mechanically operated. The continued presence of current
indicates that the breaker has failed to interrupt the circuit.
Timer 2 logic (main path) is not supervised by a breaker auxiliary contact. If fault current is detected after the delay
interval, an output is issued. This path is intended to detect a breaker that opens mechanically but fails to interrupt fault
current; the logic therefore does not use a breaker auxiliary contact.
The timer 1 and 2 paths provide two levels of current supervision, high-set and low-set, that allow the supervision level to
change from a current which flows before a breaker inserts an opening resistor into the faulted circuit to a lower level after
resistor insertion. The high-set detector is enabled after timeout of timer 1 or 2, along with a timer that enables the low-set
detector after its delay interval. The delay interval between high-set and low-set is the expected breaker opening time.
Both current detectors provide a fast operating time for currents at small multiples of the pickup value. The overcurrent
detectors are required to operate after the breaker failure delay interval to eliminate the need for very fast resetting
overcurrent detectors.
Timer 3 logic (slow path) is supervised by a breaker auxiliary contact and a control switch contact used to indicate that the
breaker is in or out-of-service, disabling this path when the breaker is out-of-service for maintenance. There is no current
level check in this logic as it is intended to detect low magnitude faults and it is therefore the slowest to operate.
Output
The outputs from the schemes are:
• FlexLogic operands that report on the operation of portions of the scheme
• FlexLogic operand used to re-trip the protected breaker
5-230
or the
BF1 N AMP SUPV PICKUP
setting, do not use a current supervised initiate. Utilize this feature for
C60 BREAKER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
BF1