5.17
Date Code 20170927 Instruction Manual SEL-751 Relay
Metering and Monitoring
Station DC Battery Monitor
Pickup settings DCLOP and DCHIP are set such that output contact OUTxxx
asserts when dc battery voltage becomes less than or greater than allowable
limits.
If the relay loses power entirely (Vdc = 0 V)
Vdc = < DCLOP
then output contact OUTxxx should logically assert (according to top of
Figure 5.18), but cannot because of the total loss of power (all output contacts
deassert on total loss of power). Thus, the resultant dc voltage element at the
bottom of Figure 5.18 would probably be a better choice—see following
discussion.
DCLO > DCHI (Bottom of Figure 5.18)
Output contact OUTxxx asserts when:
DCHIP Vdc DCLOP
Pickup settings DCLOP and DCHIP are set such that output contact OUTxxx
asserts when dc battery voltage stays between allowable limits.
If the relay loses power entirely (Vdc = 0 V)
Vdc = < DCHIP
then output contact OUTxxx should logically deassert (according to bottom of
Figure 5.18), and this is surely what happens for a total loss of power (all
output contacts deassert on total loss of power).
Additional
Application
You can use the dc voltage elements for alarming and for disabling 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 5.18. 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 8.7.
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