4.20
SEL-387-0, -5, -6 Relay
Instruction Manual
Date Code 20170601
Control Logic
SEL
OGIC
Control Equations
SEL
OGIC
Control Equations
Throughout this manual, reference is made to settings or variables that take
the form of SEL
OGIC
control equations. It is a convenient method for
providing customized control logic to the relay, to enhance the relay
performance for specific customer needs and practices.
While most users of SEL relays are at least somewhat familiar with SEL
OGIC
control equations in a general sense, the capabilities of this logic, the types of
logical operators, the number of allowable variables, and the construction
rules of the equations have varied from one relay product to another. This
portion of the manual is intended to inform the user of how SEL
OGIC
control
equations work in general and how they are implemented in the SEL-387.
SEL
OGIC
Control
Equations
Fundamental
Description
The basic building blocks of SEL
OGIC
control equations are the Relay Word
bits. A complete list of these bits is included at the end of this section of the
manual. The Relay Word bits are simple digital quantities having a logical
value of either 0 or 1. The terms “assert” or “asserted” refer to a Relay Word
bit that has a value of 1 or is changing from 0 to 1. The terms “deassert” or
“deasserted” refer to a Relay Word bit that has a value of 0 or is changing from
1 to 0. Relay Word bits are asserted or deasserted by various elements within
the relay, and are used in the fixed internal logic of the relay to make
decisions, to interpret inputs, or to drive outputs. These same bits are made
available to the user, so that the user can exercise flexibility in defining inputs
or outputs, specifying control variables for internal logic, or for creating
special customized logic through the use of SEL
OGIC
control equations.
SEL
OGIC
control equations use logic similar to Boolean algebra logic. A
SEL
OGIC
control equation consists of some combination of Relay Word bits
and logical operators that define how the Relay Word bits are to be evaluated
as a group or individually. The Relay Word bits take on their values of 0 or 1,
the operators perform logical operations on these values, and the result is a
logical value of 0 or 1 for the SEL
OGIC
control equation itself. Thus,
expressions of assertion or deassertion apply to the SEL
OGIC
control equation
as a whole, as well as to the individual components of the equation. In the end,
the SEL
OGIC
control equation itself is a simple digital variable having a value
of 0 or 1.
SEL
OGIC
Control
Equation Logical
Operators
In the SEL-387, there are six logical operators that can be used in SEL
OGIC
control equations. These operators exist in a hierarchy, from the highest level
operator to be processed to the lowest level operator.
lists these
operators in order of processing.
Table 4.7
SEL
OGIC
Control Equation Operators
Operator
Logic Function
( )
parentheses
!
NOT (negation)
/
rising edge detect
\
falling edge detect
*
AND
+
OR
Summary of Contents for SEL-387-0
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