GE B90 Instruction Manual page 205

5 SETTINGS
The breaker failure feature has two parts: breaker failure current supervision and breaker failure logic. Breaker failure cur-
rent supervision acts upon current levels and is available if the
"Protection". Breaker failure logic is based on status information and is available if the
setting is "Logic". The Breaker failure element requires B90 fiber optic interconnection and proper configura-
B90 FUNCTION
tion of the breaker failure and direct input/output settings. Refer to the Application of settings chapter for additional details.
BREAKER FAILURE PROTECTION:
In general, breaker failure schemes expect that the breaker receiving the trip command opens within a set time. If it does
not, upstream or adjacent breakers are tripped to effectively clear the fault. This widespread tripping usually interrupts
power to a larger section of the power system than the initial trip. A higher level of security is required due to the effect on
system safety and stability.
The breaker failure scheme is intended for three-pole operation but can be used with single-pole tripping if certain condi-
tions are satisfied (see the note below). The operation of the breaker failure element includes three stages: initiation, iden-
tification of a breaker failure condition, and output (or response).
The Breaker Failure can be used with single-pole tripping schemes if the
are set below the lowest expected fault current and above the highest expected load current.
NOTE
STAGE 1: INITIATION
The breaker failure scheme is initiated by a FlexLogic™ operand representing the protection trip signal initially sent to the
breaker. This signal does not include other breaker commands that are not indicative of a fault in the protected zone. The
initiating signal should be sealed-in if primary fault detection can reset before the fault is cleared. The seal-in is supervised
by current level, so it resets 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.
Breaker failure scheme 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 initiate for a breaker that has very little or no current flowing through it, which may be the
case for transformer faults or ring bus where unequal current division between ring bus circuit breakers can delay the failed
breaker clearing time until the healthy ring breaker has operated. For those situations where it is required to maintain
breaker fail coverage for fault levels below the
used. This feature should be used for those situations where coordinating margins may be reduced when high speed
reclosing is used. If this choice is made the current supervision pickup level must be lower than the minimum fault current
flowing through the breaker.
Immediately after scheme initiation it will send again trip signal to the breaker (re-trip). This is intended to reduce the possi-
bility of widespread tripping that results from a declaration of a failed breaker.
STAGE 2: DETERMINATION OF A BREAKER FAILURE CONDITION
Improved flexibility is achieved by providing three timers or stages (Timers 1, 2, and 3) as shown in the Breaker Failure
Logic diagram. Each stage is individually enabled and asserts its individual operand.
Only a breaker auxiliary contact (fast-operating) or current supervision (if enabled) can reset Timer 1 (early stage). If Timer
1 expires, it implies that current is still flowing or the breaker (position status) is still closed; that is, the breaker failed to
open. The Timer 2 (main stage) logic is not supervised by breaker status, only by current. An output is issued if current is
detected after the Timer 2 delay interval. This stage detects the condition where a breaker opens mechanically but fails to
interrupt fault current.
The and settings discriminate between the pre- and post-tripping current variation for breakers that employ
HISET LOSET
opening resistors. If the current level is between
rents above the value, the
HISET
The is based on the time that breaker resistor limited current can flow through the circuit after the
BF x LOSET TIME DELAY
breaker interruption time. Both current detectors provide fast operating time for small multiples of the pickup setting.
The Timer 3 (slow stage) is supervised by breaker status (auxiliary contact) and control switch status – the latter indicating
if the breaker is in/out of service. This mode is typically used during maintenance. There is no current level check for this
stage since this is associated with small currents. Timer 3 is typically set with a longer time.
GE Multilin
BF1 AMP SUPV PICKUP
and
HISET LOSET
timer is bypassed.
BFxx LOSET TIME DELAY
B90 Low Impedance Bus Differential System
5.5 GROUPED ELEMENTS

PRODUCT SETUP B90 FUNCTION
PRODUCT SETUP
HISET
setting, a current supervised initiate should not be
, a time delay (
BF x LOSET TIME DELAY
 setting is
B90 FUNCTION
 
B90 FUNCTION
and current elements
LOSET
) is added. For cur-
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