Sel SEL-421 - Effective Programming; Using the FLOOR Operator; Using the Negation Operator; Planning and Documentation

R.3.34
SEL-421 Relay Reference Manual Date Code 20111215
SELOGIC Control Equation Programming
Effective Programming
FLOOR
Use the FLOOR operator to round the argument to the nearest integer towards
minus infinity. Use parentheses to group a math expression as the argument of
a FLOOR operation. Example 3.21 contains examples of the FLOOR
operator.
EXAMPLE 3.21 Using the FLOOR Operator
The free-form math SEL
OGIC control equations below show examples
of the FLOOR operator usage.
# FLOOR examples
AMV001 := FLOOR (5.99) # Stores 5 in AMV001
AMV002 := FLOOR (–4.01) # Stores –5 in AMV002
Negation
Use the negation (–) operation to change the sign of the argument. The
argument of the negation operation is multiplied by –1. Negation of a positive
value results in a negative value, while negation of a negative value results in a
positive value. Example 3.22 contains examples of expressions that utilize the
negation operator.
EXAMPLE 3.22 Using the Negation Operator
The free-form math SEL
OGIC control equations below show examples
of negation operator usage.
# Negation examples
AMV001 := -AMV009 # If AMV009 is 5, stores –5 in AMV001
AMV002 := -AMV009 # If AMV009 is –5, stores 5 in AMV002
Effective Programming
This section contains several ideas useful for creating, maintaining, and
troubleshooting programming in the SEL-421 protection and automation
SEL
OGIC control equation programming environments.
Planning and
Documentation
When you begin to configure the relay to perform a new automation task or
customize protection operation, take time to design, document, and implement
your project. Scale the planning effort to match the overall size of the project,
but spend sufficient time planning to do the following:
➤ Document the inputs and outputs of your programming. This
may include protection elements, physical inputs and outputs,
metering quantities, user inputs, and other information within
the relay.
➤ Document the processing or outcome of the programming. List
the major tasks you want the relay to perform and provide
detail about the algorithm you will use for each task. For
example, if you need a timer or a counter, make a note of the
requirements and how you will use these elements.