Schweitzer Engineering SEL-387-0 - Figure 4.4 Traditional Latching Relay

4.10
SEL-387-0, -5, -6 Relay Instruction Manual Date Code 20170601
Control Logic
SEL
OGIC Control Equation Sets (1—3) Variables
Timers Reset When Power Is Lost, Settings Are Changed, or Active
Setting Group Is Changed
If power is lost to the relay, settings are changed (for the active setting group),
or the active setting group is changed, the SEL
OGIC control equation
variables/timers are reset. Relay Word bits SnVm and SnVmT are reset to
logical 0 and corresponding timer settings SnVmPU and SnVmDO load up
again after power restoration, settings change, or active setting group switch.
Latch Control
Switches
The SELOGIC control equation latch bit feature of this relay replaces latching
relays. Traditional latching relays maintain their output contact state-they are
not dependent on dc voltage to maintain their output contact state. For
example, if a latching relay output contact is closed and then dc voltage is lost
to the panel, the latching relay output contact remains closed.
The state of a traditional latching relay output contact is changed by pulsing
the latching relay inputs (see Figure 4.4). 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, etc.).
Figure 4.4 Traditional Latching Relay
The latch bits in the SEL-387 provide latching relay type functions
(Figure 4.5).
Figure 4.5 Latch Bits in SELOGIC Control Equation Sets
The output of the latch bit logic is a Relay Word bit SnLTm. The bit is set by
application of SnSLTm (Set latch bit), and reset by the application of SnRLTm
(Reset latch bit). The Set/Reset values come from the logical state of the
SEL
OGIC control equations stored for these two settings. These latch bits may
be used in SEL
OGIC control equations, wherever a latching function is
required.
contact
output
inputinput
Traditional Latching Relay
resetset
(–)
(+)
S
nLT
m
S
n
S
LT
m
S
nRLT
m
(
set
)
(
reset
)
S
E
L
OG
I
C
Co
n
t
r
o
l
E
q
uation Settin
gs
n
= SELOGIC
control e
q
uation set number
m
= Variable number
Rela
y
W
o
r
d
Bi
t