7.14
SEL-351A Relay
Instruction Manual
Date Code 20080213
Inputs, Outputs, Timers, and Other Control Logic
Latch Control Switches
If the SCADA contact deasserts and then asserts again (new rising edge—see
Pulse 2 in
), the “reset” input (setting RST1) asserts and latch bit
LT1 deasserts back to logical 0 again. Thus, each individual assertion of input
IN104
(Pulse 1, Pulse 2, Pulse 3, and Pulse 4 in
) changes the state
of the latch control switch just once.
Figure 7.14
Latch Control Switch Operation Time Line
Use a Remote Bit to Enable/Disable the Reclosing Relay
Use a remote bit to enable/disable the reclosing relay, instead of an
optoisolated input. For example, substitute remote bit RB1 for optoisolated
input
IN104
in the settings accompanying
:
SET1 =
/RB 1 * !LT1
[= (rising edge of remote bit RB1) AND NOT(LT1)]
RST1 =
/RB1 * LT1
[= (rising edge of remote bit RB1) AND LT1]
79DTL =
!LT1
[= NOT(LT1); drive-to-lockout setting]
Pulse remote bit RB1 to enable reclosing, pulse remote bit RB1 to disable
reclosing, etc., much like the operation of optoisolated input
IN104
in the
previous example. Remote bits (Relay Word bits RB1–RB16) are operated
through the serial port. See
for more information on remote bits.
These are just a few control logic examples—many variations are possible.
Latch Control Switch
States Retained
Power Loss
The states of the latch bits (LT1–LT16) are retained if power to the relay is lost
and then restored. If a latch bit is asserted (e.g., LT2 = logical 1) when power
is lost, it comes back asserted (LT2 = logical 1) when power is restored. If a
latch bit is deasserted (e.g., LT3 = logical 0) when power is lost, it comes back
deasserted (LT3 = logical 0) when power is restored. This feature makes the
latch bit feature behave the same as traditional latching relays. In a traditional
installation, if power is lost to the panel, the latching relay output contact
position remains unchanged.
RST1 = /IN104 * LT1
/IN104
IN104
SET1 = /IN104 * !LT1
Rising
Edge
One
Processing
Interval
Pulse 1
Pulse 2
Pulse 3
Pulse 4
Rising
Edge
Rising
Edge
Rising
Edge
LT1
NOTE:
If a latch bit is set to a
programmable output contact (e.g.,
OUT103 = LT2) and power to the relay
is lost, the state of the latch bit is
stored in nonvolatile memory but the
output contact will go to its
de-energized state. When power to
the relay is restored, the
programmable output contact will go
back to the state of the latch bit after
relay initialization.
Summary of Contents for SEL-351A
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