5.13
Date Code 20100129
Instruction Manual
SEL-751A Relay
Metering and Monitoring
Station DC Battery Monitor
Figure 5.16
Create DC Voltage Elements With SEL
OGIC
Control Equations
DCLO < DCHI (Top of
)
Output contact OUT
xxx
asserts when:
V
dc
≤
DCLOP or V
dc
≥
DCHIP
Pickup settings DCLOP and DCHIP are set such that output contact OUT
xxx
asserts when dc battery voltage goes below or above allowable limits.
If the relay loses power entirely (V
dc
= 0 V)
V
dc
= < DCLOP
then output contact OUT
xxx
should logically assert (according to top of
), 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
would probably be a better choice—see following
discussion.
DCLO > DCHI (Bottom of
)
Output contact OUT
xxx
asserts when:
DCHIP
≤
V
dc
≤
DCLOP
Pickup settings DCLOP and DCHIP are set such that output contact OUT
xxx
asserts when dc battery voltage stays between allowable limits.
If the relay loses power entirely (V
dc
= 0 V)
V
dc
= < DCHIP
then output contact OUT
xxx
should logically deassert (according to bottom of
), and this is surely what happens for a total loss of power (all
output contacts deassert on total loss of power).
SV
n
PU
SV
n
DO
SV
n
SV
n
T
SV
n
T
DCHI
SV
n
= DCLO + DCHI
OUT
xxx
= SV
n
T
DCLO
DCLOP
DCHIP
DCLOP
<
DCHIP
Vdc
SV
n
PU
SV
n
DO
SV
n
DCLO * DCHI
SV
n
= DCLO * DCHI
OUT
xxx
= SV
n
T
DCLOP
DCHIP
DCLOP
>
DCHIP
Vdc
Summary of Contents for 751A
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