R.3.12
SEL-421 Relay Reference Manual Date Code 20111215
SELOGIC Control Equation Programming
SELOGIC Control Equation Elements
SELOGIC Control Equation Elements
SELOGIC control equation elements are a collection of storage locations,
timers, and counters that you can use to customize the operation of your
SEL-421 and use the relay to automate substation operation. The elements
that you can use in SEL
OGIC control equations are summarized in Tab le 3. 5.
Relay Word Bits and
Analog Quantities
Data within the relay are available for use in SELOGIC control equations.
Relay Word bits are binary data that include protection elements, input status,
and output status. Appendix A: Relay Word Bits contains a list of Relay Word
bits available within the SEL-421. Analog quantities are analog values within
the relay including measured and calculated values. Appendix B: Analog
Quantities in the Reference Manual contains a list of analog quantities
available within the SEL-421.
Special Condition Bits
Several Relay Word bits are available for special conditions related to
SEL
OGIC control equation programming in the SEL-421. You can use these
bits in SEL
OGIC control equation programming to react to these conditions.
You can also send these bits to other devices through relay interfaces including
M
IRRORED BITS communications and DNP3. The special condition bits are
shown in Table 3.6.
The relay sets the first execution bits AFRTEXA, AFRTEXP, and PFRTEX
momentarily to allow you to detect changes in the relay operation. The relay
sets these bits and clears them as described in Table 3.6, Table 3.7, and
Tab le 3.8. You can use these bits to force logic and calculations to reset or take
a known state on power-up or settings change operations.
Table 3.5 Summary of SELOGIC Control Equation Elements
Element Description
Relay Word bits Boolean value data
Analog quantities Received, measured, and calculated values
Special condition bits Bits that indicate special SEL
OGIC control
equation execution conditions
SEL
OGIC control equation variables Storage locations for the results of Boolean
SEL
OGIC control equations
SEL
OGIC control equation math variables Storage locations for the results of math
SEL
OGIC control equations
Latch bits Nonvolatile storage for the results of Bool-
ean SEL
OGIC control equations
Conditioning timers Pickup and dropout style timers similar to
those used in SEL-300 series relays
Sequencing timers On-delay timers similar to those used in
programmable logic controllers
Counters Counters that count rising edges of Boolean
value inputs
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