Schweitzer Engineering Laboratories SEL-351-5, Instruction Manual

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7.12
SEL-351-5, -6, -7 Relay Instruction Manual
Date Code 20070117
Inputs, Outputs, Timers, and Other Control Logic
Latch Control Switches
Latch Control Switches
The latch control switch feature of this relay replaces latching relays.
Traditional latching relays maintain their output contact state when set. The
SEL-351 latch bit retains memory even when control power is lost. If the latch
bit is set to a programmable output contact and control power 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 the control power is applied back to the relay,
the programmed output contact will go back to the state of the latch bit after
relay initialization.
The state of a traditional latching relay output contact is changed by pulsing
the latching relay inputs (see
Figure 7.11 ). Pulse the set input to close (“set”)
the latching relay output contact. Pulse the reset input to open (“reset”) the
latching relay output contact. Often the external contacts wired to the latching
relay inputs are from remote control equipment (e.g., SCADA, RTU).
Figure 7.11 Traditional Latching Relay
The sixteen (16) latch control switches in the SEL-351 provide latching relay
type functions.
Figure 7.12 Latch Control Switches Drive Latch Bits LT1–LT16
The output of the latch control switch in Figure 7.12 is a Relay Word bit LT n
( n = 1 through 16), called a latch bit. The latch control switch logic in
Figure 7.12 repeats for each latch bit LT1–LT16. Use these latch bits in
SEL
OGIC
control equations.
These latch control switches each have the following SEL
OGIC
control
equation settings:
SET n (set latch bit LT n to logical 1)
RST n (reset latch bit LT n to logical 0)
If setting SET n asserts to logical 1, latch bit LT n asserts to logical 1. If setting
RST n asserts to logical 1, latch bit LT n deasserts to logical 0. If both settings
SET n and RST n assert to logical 1, setting RST n has priority and latch bit LT n
deasserts to logical 0.
Output
Contact
Traditional Latching Relay
Reset
Input
Set
Input
(—)
(+)
LTn
SETn
RSTn
(Set)
(Reset)
(n = 1 through 16)
Relay
Word
Bits
SEL
OGIC
Setting