Schweitzer Engineering Laboratories SEL-421-4 Instruction Manual page 1179

Protection Latch Bits
Date Code 20171006
Table 13.8 Latch Bit Parameters
Type Item Description
Input Reset Reset latch when on
Input Set Set latch when on
Output Latched Latched Value of 0 or 1 Value for use in Boolean SEL
Value
Latch bits provide nonvolatile storage of binary information. A latch can have the
value of logical 0 or logical 1. Latch bits also retain their state through changes in
the active protection settings group. Because storage of latch bits is in nonvolatile
memory, the state of latch bits remains unchanged indefinitely, even when power
is lost to the relay.
As with logic latches used in digital electronics, each latch bit has a Set input and
a Reset input. The relay evaluates the latch bit value at the end of each logic pro-
cessing interval using the values for Set and Reset calculated during the process-
ing interval. Latch bits are reset dominant. If the Set and Reset inputs are both
asserted, the relay will reset the latch.
Latch bits are available in two different programming areas of the relay. First,
there are 32 latch bits, PLT01–PLT32, that are associated with protection set-
tings. Second, there are 32 latch bits, ALT01–ALT32, available in automation
freeform programming. You can view the status of individual latch bits in the
Relay Word using the TARGET command. Use the TAR PLTnn command or
the TAR ALTnn command to view the Relay Word row containing the protec-
tion or automation latch bit specified by the two-digit number, nn. You can also
view the status of latch bits through the relay LCD front-panel display by select-
ing from the Main Menu and scrolling through the rows of
RELAY ELEMENTS
Relay Word bits.
Program the 32 latch bits, PLT01–PLT32, in the protection freeform SEL
control equation programming area. There is a separate protection freeform
SEL control equation programming area associated with each protection set-
OGIC
tings group. The latches in protection can have separate programming for Set and
Reset in each protection settings group. While each protection latch value
remains unchanged for a change in the active protection settings group, you can
enter different Set and Reset programming for each protection settings group.
There are Set and Reset settings for each latch bit available in each group. For
example, PLT01R and PLT01S are available in all six freeform settings groups
and all control the same Latch Bit, PLT01. This structure allows you to either
program each latch to operate in the same way for each group or behave differ-
ently based on the active protection settings group. For example, you could pro-
gram the protection latch to set on IN107 when Protection Settings Group 1 is
active and program the latch to set on IN106 when Protection Settings Group 2 is
active. If you do not enter a setting for the Reset and Set in a protection settings
group, the latch bit will remain unchanged when that protection settings group is
active. Example 13.6 illustrates protection latch bit usage.
Instruction Manual
SEL Control Equation Programming
OGIC
SEL Control Equation Elements
OGIC
Setting
Boolean SEL control equation PLT01R
OGIC
Boolean SEL control equation PLT01S
OGIC
OGIC
control equations
13.13
Name
Examples
ALT01R
ALT01S
PLT01
ALT24
OGIC
SEL-400 Series Relays