12
SEL-FT50/SEL-FR12 Fault Transmitter and Receiver System
Instruction Manual
Date Code 20210405
Application Examples
Implement a Low-Cost Fast Bus-Tripping Scheme
A fast bus-tripping scheme uses a short-time delayed overcurrent element in the
bus relay to provide a quick response to bus faults. To maintain coordination for
feeder faults, the scheme must block this fast element operation whenever a
feeder relay or recloser control is picked up and timing. Traditional fast bus-trip
schemes use a hardwired control circuit or communications link to allow each
feeder relay to drive a bus relay block signal when a fault occurs on a distribution
line outside the substation.
In stations without bus differential or a fast bus-tripping scheme, a bus fault has a
long duration because the bus relay only uses a time-overcurrent element coordi-
nated with the feeder protection.
In some substations, installing a fast bus-trip scheme is not feasible because the
feeder pickup-based block signal cannot be created or transmitted through nor-
mal means. For example, some feeder protection devices (reclosers or relays)
may not be able to provide a block signal, or the device may be located far across
a substation yard, requiring a costly cable or fiber run to bring a block signal back
to the bus relay panel.
Figure 12
shows a substation one-line diagram with a
recloser on each feeder. Retrofitting a traditional fast bus-tripping scheme to this
type of substation might be expensive.
Instead of installing wiring or upgrading equipment, use the SEL-FT50/
SEL-FR12 Fault Transmitter and Receiver System to bring in the required feeder
pickup signal without making changes to the medium voltage system.
In
Figure 12
, each feeder (A through D) is equipped with SEL-FT50 transmitters.
An example fault F1 on Feeder D triggers one or more of the SEL-FT50 transmit-
ters to transmit. The SEL-FR12 receives the transmission and immediately sends
the fault status to the bus relay. At the same time, the bus relay is also picked-up
and timing the
respective definite-time overcurrent element. As soon as the
SEL-FR12 fault signal arrives, the bus relay blocks the respective definite-time
overcurrent element and maintains the block state until the overcurrent element
has completely reset. The Feeder Recloser D operates as needed to clear the fault
or lockout the line.
For a bus fault F2, none of the SEL-FT50 transmitters trigger for fault current,
and the bus relay receives no fault signal from the SEL-FR12. In this situation,
the bus relay fast-acting definite-time overcurrent element times out and trips the
bus breaker after a brief coordination delay.
Figure 11
Feeder Cable Egress Protection With Enhancements
SEL-FR12
Relay
Breaker
Substation bus
Substation
Underground
feeder cable
Wireless
Riser pole
Overhead conductor
SEL-FT50
