CHAPTER 5: SETTINGS GROUPED ELEMENTS
B90 LOW IMPEDANCE BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 5-163
5
5.6.4.5 Breaker failure settings
BF1 INITIATE — This setting selects the FlexLogic operand that initiates three-pole tripping of the breaker. Although this
scheme is designed for three-pole tripping, it can be used with single-pole tripping schemes if the HISET and LOSET current
elements are set to be sensitive to the lowest expected fault value but insensitive to the highest expected load on the
protected line.
BF1 USE AMP SUPV — If set to "Yes", the element is initiated if current flowing through the breaker is above the supervision
pickup level.
BF1 USE SEAL-IN — If set to "Yes", the element is sealed-in if current flowing through the breaker is above the supervision
pickup level.
BF1 AMP SUPV OP A through C — This setting selects the B90 Remote Inputs that represent operation of the current
supervision elements on phase A, B, or C.
BF1 USE TIMER 1 — If set to "Yes", the Early Path is operational.
BF1 TIMER 1 PICKUP DELAY — Timer 1 is set to the shortest time required for breaker auxiliary contact BKR POS1 to open, from
the time the initial trip signal is applied to the breaker trip circuit, plus a safety margin
BF1 USE TIMER 2 — If set to "Yes", the Main Path is operational.
BF1 TIMER 2 PICKUP DELAY — Timer 2 is set to the expected opening time of the breaker, plus a safety margin. This safety
margin was historically intended to allow for measuring and timing errors in the breaker failure scheme equipment. In
microprocessor relays this time is not significant. In UR relays, which use a Fourier transform, the calculated current
magnitude ramps-down to zero one power frequency cycle after the current is interrupted, and this lag should be included
in the overall margin duration, as it occurs after current interruption. The Breaker Failure Main Path Sequence diagram
shows a margin of two cycles; this interval is considered the minimum appropriate for most applications.
In bulk oil circuit breakers, the interrupting time for currents less than 25% of the interrupting rating can be significantly
longer than the normal interrupting time.
BF1 USE TIMER 3 — If set to "Yes", the Slow Path is operational.
BF1 TIMER 3 PICKUP DELAY — Timer 3 is set to the same interval as Timer 2, plus an increased safety margin. Because this
path is intended to operate only for low level faults, the delay can be in the order of 300 to 500 ms.
BF1 BKR POS1 — This setting selects the FlexLogic operand that represents the protected breaker early-type auxiliary switch
contact (52/a). This is normally a non-multiplied Form-A contact. The contact may even be adjusted to have the shortest
possible operating time.
BF1 BKR POS2 — This setting selects the FlexLogic operand that represents the protected breaker normal type auxiliary
switch contact (52/a). This may be a multiplied contact.
BF1 BKR TEST ON — This setting selects the FlexLogic operand that represents the breaker In-Service/Out-of-Service switch,
set to the Out-of-Service position.
BF1 LOSET TIME DELAY — This setting represents the pickup delay for current detection after opening resistor insertion.
Typically this is based on the time while the breaker resistor current can flow through the circuit after the breaker
interrupting time.
BF1 TRIP DROPOUT TIME DELAY — This setting is used to set the period of time for which the trip output is sealed-in. This timer
must be coordinated with the automatic reclosing scheme of the failed breaker, to which the breaker failure sends a cancel
reclosure signal. Reclosure of a remote breaker can also be prevented by holding a Transfer Trip signal on longer than the
"reclaim" time.
BF1 RETRIP TIME DELAY — This setting is used to set a delay before asserting the re-trip operand.
BF1 CT — This setting selects the currents that will be used in Breaker Failure scheme BF1 for current supervision (AMP
SUPV, HISET and LOSET elements).
BF1 AMP SUPV PICKUP — This setting is used to set the phase current initiation and seal-in supervision level. Generally this
setting should detect the lowest expected fault current on the protected breaker. It can be set as low as necessary (lower
than breaker resistor current or lower than load current). HISET and LOSET current supervision guarantee correct
operation.
BF1 AMP HISET PICKUP — This setting is used to set the phase current fault detection level. Generally this setting detects the
lowest expected fault current on the protected breaker, before a breaker-opening resistor is inserted.
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