4.48
SEL-749M Relay Instruction Manual Date Code 20080918
Protection and Logic Functions
Logic Functions
If RB3 is initially at logical 0, pulsing it with the CON 3 command and PRB 3
subcommand will change RB3 to logical 1 for one processing interval and
then return it to logical 0. In this situation, the R_TRIG RB3 (rising edge
operator) will also assert for one processing interval, followed by the F_TRIG
RB3 (falling edge operator) one processing interval later.
If RB3 is initially at logical 1 instead, pulsing it with the CON 3 command
and PRB 3 subcommand will change RB3 to a logical 0. In this situation, the
R_TRIG RB3 (rising edge operator) will not assert, but the F_TRIG RB3
(falling edge operator) will assert for one processing interval.
Latch Bits
Latch control switches (latch bits are the outputs of these switches) replace
traditional latching relays. Traditional latching relays maintain output contact
state. The SEL-749M latch control switches also retain state even when power
to the relay is lost. If the latch control switch is set to a programmable output
contact and power to the relay is lost, the state of the latch control switch is
stored in nonvolatile memory, but the relay de-energizes the output contact.
When power to the relay is restored, the programmable output contact will go
back to the state of the latch control switch after relay initialization.
Traditional latching relay output contact states are changed by pulsing the
latching relay inputs (see Figure 4.28). Pulse the set input to close (set) the
latching relay output contact. Pulse the reset input to open (reset) the latching
relay output contact. The external contacts wired to the latching relay inputs
are often from remote control equipment (e.g., SCADA, RTU).
Figure 4.28 Traditional Latching Relay
Eight latch control switches in the SEL-749M provide latching relay
functionality.
Figure 4.29 Latch Control Switches Drive Latch Bits LT01—LT08
The output of the latch control switch in Figure 4.29 is a Relay Word bit LTn
(n = 01–08), called a latch bit. The latch control switch logic in Figure 4.29
repeats for each latch bit LT01–LT08. Use these latch bits in SEL
OGIC control
equations.
These latch control switches each have the following SEL
OGIC control
equation settings:
SETn (set latch bit LTn to logical 1)
RSTn (reset latch bit LTn to logical 0)
Set
Input
Reset
Input
Output
Contact
Traditional
Latching
Relay
(+)
(–)
LTn
SETn
RSTn
(Set)
(Reset)
(n = 1 through 08)
Relay
Word
Bits
SEL
OGIC
Setting
Courtesy of NationalSwitchgear.com
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