GE D90 Plus Instruction Manual page 285

CHAPTER 7: PROTECTION
Breaker failure scheme outputs
Breaker failure settings and logic
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
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 will
enable 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/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.
The outputs from the breaker failure scheme are:
• FlexLogic™ operands that report on the operation of portions of the scheme.
• A FlexLogic™ operand used to re-trip the protected breaker.
• FlexLogic™ operands that initiate tripping required to clear the faulted zone. The trip
output can be sealed-in for an adjustable period.
• Illumination of a front panel annunciator message or messages.
Select the Settings > Protection > Elements > Group 1 > Breaker Failure menu item to
open the breaker failure configuration window.
GROUPED PROTECTION ELEMENTS
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