Sel 751A - Additional Application; Analyze Station DC Battery Voltage; Station DC Battery Voltage Dips During Circuit Breaker Tripping; View Station DC Battery Voltage

5.14
SEL-751A Relay Instruction Manual Date Code 20100129
Metering and Monitoring
Station DC Battery Monitor
Additional
Application
Other than alarming, the dc voltage elements can be used to disable reclosing.
For example, if the station dc batteries have a problem and the station dc
battery voltage is declining, drive the reclosing relay to lockout:
79DTL = NOT(SVnT) OR....
Timer output SVnT is from the bottom of Figure 5.16. When dc voltage falls
below pickup DCHIP, timer output SVnT drops out (= logical 0), driving the
relay to lockout:
79DTL = NOT(SVnT) OR ... = NOT(logical 0) OR ... = logical OR
Circuit breaker tripping and closing requires station dc battery energy. If the
station dc batteries are having a problem and the station dc battery voltage is
declining, the relay should not reclose after a trip—there might not be enough
dc battery energy to trip a second time after a reclose.
View Station DC
Battery Voltage
Via Serial Port
The METER command displays the station dc battery voltage (labeled VDC).
Via Front Panel
The information available via the previously discussed METER serial port
command is also available via the front-panel Meter Menu. See Figure 8.6.
Analyze Station DC
Battery Voltage
The station dc battery voltage is displayed in column Vdc in the example
event report in Figure 9.3. Changes in station dc battery voltage for an event
(e.g., circuit breaker tripping) can be observed. Use the EVE command to
retrieve event reports as discussed in Section 9: Analyzing Events.
Station DC Battery Voltage Dips During Circuit Breaker Tripping
Event reports are automatically generated when the TRIP Relay Word bit
asserts (TRIP is the logic output of Figure 4.29). For example, output contact
OUT103 is set to trip:
OUT103 = TRIP
Anytime output contact OUT103 closes and energizes the circuit breaker trip
coil, any dip in station dc battery voltage can be observed in column Vdc in
the event report.
To generate an event report for external trips, program an optoisolated input
INxyz (monitoring the trip bus) in the SEL
OGIC control equation event report
generation setting:
ER = R_TRIG(INxyz) OR…
Anytime the trip bus is energized, any dip in station dc battery voltage can be
observed in column Vdc in the event report.