GE B90 Instruction Manual page 226

5.5 GROUPED ELEMENTS
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.
5
• EFP1 PICKUP: Specifies the current level recognized by an armed EFP scheme as fault current in the protected dead-
zone. Although it can be set very low (above the noise level), set above the maximum load current for extra security.
• EFP1 BREAKER OPEN: This setting is a FlexLogic™ operand indicating an open breaker. The operand shall be "On"
when the breaker is open. Typically, this setting is a position of an appropriately wired input contact of the B90.
• EFP1 BKR DELAY: This setting specifies a timed delay between the breaker position being declared as open by the
EFP1 BREAKER OPEN
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.
• EFP1 MANUAL CLOSE: This setting is a FlexLogic™ operand indicating a close command for the breaker. This oper-
and shall be "On" when the breaker is ordered to close. Typically this setting is a position of an appropriately wired
input contact of the B90.
• EFP1 PICKUP DELAY: This setting allows extra security when tripping the bus from the EFP element. This timer shall
be set longer than the maximum delay between the breaker closing and picking up some current and the EFP MAN-
UAL CLOSE signal. If the manual close signal, EFP MANUAL CLOSE, arrives before the timer expires, the element
resets and misoperation due to signal transit times is avoided.
• EFP1 BLOCK: This setting dynamically block/unblocks the element. A typical application is a by-pass isolator as
shown below. When the isolator is closed, the current does not necessarily indicate on a fault between the CB and CT
and the element shall be blocked. Therefore, the close status of the isolator shall be used as the block setting.
5-106
a: Bus-side CTs
BUS ZONE
"dead-zone"
(requires
tripping the bus)
Figure 5–47: APPLICATION OF END FAULT PROTECTION ELEMENT
setting and the moment the EFP scheme is armed. Set this delay long enough to avoid spurious
TRANSFER BUS
selective
"dead-zone"
only if the
isolator is open
Figure 5–48: END FAULT PROTECTION AND BY-PASS ISOLATORS
B90 Low Impedance Bus Differential System
b: Line-side CTs
BUS ZONE
"dead-zone"
(requires inter-
tripping)
BUS SECTION
CB ISO
5 SETTINGS
GE Multilin