7.12
SEL-351A Relay Instruction Manual Date Code 20080213
Inputs, Outputs, Timers, and Other Control Logic
Latch Control Switches
Latch Control Switch
Application Ideas
Latch control switches can be used for such applications as:
➤ Reclosing relay enable/disable
➤ Ground relay enable/disable
➤ Sequence coordination enable/disable
Latch control switches can be applied to almost any control scheme. The
following is an example of using a latch control switch to enable/disable the
reclosing relay in the SEL-351A.
Reclosing Relay
Enable/Disable
Setting Example
Use a latch control switch to enable/disable the reclosing relay in the
SEL-351A. In this example, a SCADA contact is connected to optoisolated
input IN104. Each pulse of the SCADA contact changes the state of the
reclosing relay. The SCADA contact is not maintained, just pulsed to enable/
disable the reclosing relay.
Figure 7.12 SCADA Contact Pulses Input IN104 to Enable/Disable Reclosing
Relay
If the reclosing relay is enabled and the SCADA contact is pulsed, the
reclosing relay is then disabled. If the SCADA contact is pulsed again, the
reclosing relay is enabled again. The control operates in a cyclic manner:
pulse to enable ... pulse to disable ... pulse to enable ... pulse to disable ...
This reclosing relay logic is implemented in the following SEL
OGIC control
equation settings and displayed in Figure 7.13.
SET1 = /IN104 * !LT1 [= (rising edge of input IN104) AND NOT(LT1)]
RST1 = /IN104 * LT1 [= (rising edge of input IN104) AND LT1]
79DTL = !LT1 [= NOT(LT1); drive-to-lockout setting]
Figure 7.13 Latch Control Switch Controlled by a Single Input to Enable/
Disable Reclosing
(+)
SCADA
(—)
Enable/Disable Reclosing Relay
SEL-351
IN104
LT1
IN104
(Set)
(Reset)
Rising-Edge
Detect
SET1
RST1
SELOGIC
Setting
SELOGIC
Setting
Relay
Word
Bit
Relay
Word
Bit
Courtesy of NationalSwitchgear.com
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