GE C70 Instruction Manual page 316

GROUPED ELEMENTS
In general, a breaker failure scheme determines that a breaker signaled to trip has not cleared a fault within a definite
time, so further tripping action must be performed. Tripping from the breaker failure scheme should trip all breakers, both
5
local and remote, that can supply current to the faulted zone. Usually operation of a breaker failure element causes
clearing of a larger section of the power system than the initial trip. Because breaker failure can result in tripping a large
number of breakers and this affects system safety and stability, a very high level of security is required.
Two schemes are provided: one for three-pole tripping only (identified by the name "3BF") and one for three pole plus
single-pole operation (identified by the name "1BF"). The philosophy used in these schemes is identical. The operation of a
breaker failure element includes three stages: initiation, determination of a breaker failure condition, and output.
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.
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 immediately sends a trip signal 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.
5-192
BF1 TRIP DROPOUT

DELAY: 0.000 s
BF1 TARGET:

Self-Reset
BF1 EVENTS:

Disabled
BF1 PH A INITIATE:

Off
BF1 PH B INITIATE:

Off
BF1 PH C INITIATE:

Off
BF1 BKR POS1

Off
BF1 BKR POS1

Off
BF1 BKR POS2

Off
BF1 BKR POS2

Off
or the
BF1 N AMP SUPV PICKUP
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
Range: 0.000 to 65.535 s in steps of 0.001
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
Range: FlexLogic operand
Valid only for 1-Pole breaker failure schemes
Range: FlexLogic operand
Valid only for 1-Pole breaker failure schemes
Range: FlexLogic operand
Valid only for 1-Pole breaker failure schemes
φ
B: Range: FlexLogic operand
Valid only for 1-Pole breaker failure schemes
φ
C: Range: FlexLogic operand
Valid only for 1-Pole breaker failure schemes
φ
B: Range: FlexLogic operand
Valid only for 1-Pole breaker failure schemes
φ
C: Range: FlexLogic operand
Valid only for 1-Pole breaker failure schemes
setting, do not use a current supervised initiate. Utilize this feature for
CHAPTER 5: SETTINGS
BF1