GE B90 Instruction Manual page 369

CHAPTER 5: SETTINGS
The End Fault Protection (EFP) element operates for dead-zone faults; i.e., faults between the CT and an open feeder
breaker. Since a bus protection zone terminates on the CTs, faults between the CT and breaker require special
consideration.
With a bus-side CT (Part A of the figure below), a fault between the open CB and CT is outside the bus zone but can only
cleared by tripping the bus zone protection. In this case EFP trips the bus zone protection once the current exceeds a user-
programmable threshold, effectively clearing the fault.
With a line-side CT (Part B of the figure below), the zone is reduced once the breaker opens. Otherwise, the bus protection
may issue an unnecessary widespread trip in the case of a fault between the open CB and CT. The zone is shortened using
the breaker position with a short drop-out delay as a connection status for the associated current. Once the bus zone
moves and terminates on the CB, a dead-zone is created between the CB and CT. In this case, the EFP is used; upon
operation, the EFP will trip the remote breaker.
The EFP element arms when the feeder breaker opens and resets when a manual breaker CLOSE command is issued. To
avoid race conditions, a user-programmable time delay for the breaker OPEN signal is provided. Once armed, the element
operates when the current exceeds a user-programmable threshold. The output must be configured to either send an
inter-trip or trip the bus zone protection depending on the CT orientation with respect to the breaker.
— Specifies the current level recognized by an armed EFP scheme as fault current in the protected dead-zone.
EFP1 PICKUP
Although it can be set very low (above the noise level), set above the maximum load current for extra security.
— This setting is a FlexLogic operand indicating an open breaker. The operand shall be "On" when the
EFP1 BREAKER OPEN
breaker is open. Typically, this setting is a position of an appropriately wired input contact of the B90.
— This setting specifies a timed delay between the breaker position being declared as open by the EFP1
EFP1 BKR DELAY
BREAKER OPEN setting and the moment the EFP scheme is armed. Set this delay long enough to avoid spurious operation
due to a delay between the breaker position and decaying of the breaker current. The current ramp down period of the
B90 for the purpose of setting the EFP is 1.3 of a power system cycle.
— This setting is a FlexLogic operand indicating a close command for the breaker. This operand shall
EFP1 MANUAL CLOSE
be "On" when the breaker is ordered to close. Typically this setting is a position of an appropriately wired input contact of
the B90.
B90 LOW IMPEDANCE BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
EFP1 BLOCK:

Off
EFP1 TARGET:

Self-reset
EFP1 EVENTS:

Disabled
Figure 5-93: Application of end fault protection element
GROUPED ELEMENTS
Range: FlexLogic operand
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
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