9328900990 Rev L BE1-951 Application 8-33
Normal Operation - Bus Protection
During normal operation, the primary task of the BUS relay is to provide high-speed fault protection (2 to
4 cycles coordination interval) and timed overload or high unbalanced load protection. The primary task of
the BACKUP relay is to provide the BUS relay with backup support for bus faults with an 18 to 20-cycle
coordination interval.
When any feeder relay overcurrent element is picked up and timing, OUT4 of the feeder relay closes.
OUT4 is intended to be connected to IN2 of the upstream (primary) bus relay that is using BUS logic.
When IN2 is energized, the bus relay 50T elements (2 to 4 cycle time delay) are blocked. If a fault occurs
that is not on a feeder, then the bus relay 50T elements are not blocked. The bus relay 50T function
blocks are set up close OUT4 that will trip the bus breaker by an external bus lockout relay (86B).
Because the BACKUP relay isn't blocked when a feeder relay picks up, its 50T elements are set with a
time delay long enough to allow the feeder breaker to interrupt a fault. The BACKUP 50T elements are
set up to trip the 86B relay via OUTA. If a bus-fault lockout relay isn't used, OUT4 can be wired in parallel
with OUT1 to directly trip the bus breaker. The BUS and BACKUP 50T functions should be set with a
higher pickup than the highest feeder instantaneous elements to ensure that they won't pickup before any
feeder relay.
If there is a contingency problem such as a relay removed from service, 51 protection is still provided. The
BUS and BACKUP 51 functions are enabled for tripping via OUT1. The 51 functions aren't blocked to
allow clearing of a bus fault with a traditional coordination interval. When used to provide high-speed
overcurrent protection for the substation bus, it is recommended that all 51 function timing curves be set
for instantaneous reset.
Normal Operation - Setting Group Selection
For normal operation, the BUS and BACKUP relays use Setting Group 0. In Setting Group 0, the two
relays will only trip the bus breaker. IN2 of the BACKUP relay identifies when a feeder relay is out of
service. The BACKUP relay will close OUT3, which is connected to IN3 of the BUS relay. Both relays then
switch to Setting Group 1. Binary coded setting group selection (Mode 2) is used to recognize the group
setting state. When input D0 of the setting group selection function block is logic 1 (TRUE), it is
interpreted as a binary 1 and causes the logic to switch to Setting Group 1.
When in Setting Group 1, the relays are operating in feeder relay backup mode. This expression is
programmed to VO13 of the BUS relay that drives alarm bit 21 in the programmable alarm mask. Alarm
bit 21 can be masked to drive an alarm LED and Alarm Screen to indicate when the BUS relay is in
feeder backup mode. It can also be used to trip a feeder breaker instead of the bus breaker.
More information about setting group operation is provided in the Setting Group subsection of Section 4,
Protection and Control.
Normal Operation - Alarms
If the continuous self-test diagnostics of the relay detect an error, failsafe output contact OUTA will
change states and the Relay Trouble LED of the HMI will light. OUTA will also change states if relay
operating power is lost. More information about alarms is provided in Section 6, Reporting and Alarm
Functions.
Contingency Operation - Test Mode
The test mode is intended to increase the security of the protection and control system if external test
switches are not installed on all outputs.
De-energizing IN4 or closing Virtual Switch 343 places the logic scheme in test mode. IN4 can be
controlled by a panel mounted selector switch that is closed in the normal state and open in the test state.
IN4 can also be controlled by a pole of a standard external test switch that is opened with the rest of the
test switch poles. When test mode is activated in the BUS relay, external breaker failure initiate (BFI) via
VO3 is inhibited. The BACKUP relay will block its own breaker failure function while test mode is enabled.
The logic for test mode drives VO15, which drives alarm bit 23 in the programmable alarm mask. Alarm
bit 23 can be masked to drive an alarm LED and HMI Alarm Screen to provide indication when the relay
is in test mode.
Contingency Operation - Backup Protection for Bus Breaker Failure
Bus breaker-failure protection is provided by the main bus relay using the preprogrammed logic scheme
BACKUP. OUT5 is configured as the breaker failure trip output. OUT5 can be wired to trip the upstream
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