4.197
Date Code 20170814
Instruction Manual
SEL-700G Relay
Protection and Logic Functions
Logic Settings (SET L Command)
The relay converts variables from decimal to integer before performing math
operations (through multiplication by 128 followed by rounding). After the
math operations, the relay converts the result back from integer to decimal by
scaling the value down by 128 before reporting the results. This effectively
means that math calculations are rounded. See Example 4.6 for an explanation
on improving the accuracy of the math operations by managing the processing
order.
EXAMPLE 4.6
Improving the Accuracy of Math Operations
If MV01 := (60/4160) • 100,000, the relay performs the 60/4160
calculation and scales it by 128, then rounds this up to 2. The relay then
multiplies it by 100,000 and stores it as 200,000. When the number is
reported, the relay divides out the scale factor (128) and reports
1562.5.
Alternatively, if MV01 := (60 • 100,000)/4160, the relay multiplies
(60 • 100,000), then scales by 128, and then divides by 4160. This result
is then rounded and stored as 184,615. The relay then divides 184,615
by 128 and reports 1442.3.
Example 4.6 illustrates the importance of avoiding calculations where a small
number is divided by a large number followed by multiplication. Such
calculations amplify any error significantly.
The executed result of a math SEL
OGIC
control equation is stored in a math
variable. The smallest and largest values a math variable can represent are
–16777215.99 and +16777215.99, respectively. If the executed result exceeds
these limits, it is clipped at the limit value. For example, when the
MV01 := executed result is –16777219.00, MV01 will be –16777215.99.
Similarly, when the MV02 := executed result is +16777238.00, MV02 will be
+16777215.99.
Comments can be added to both Boolean and math SEL
OGIC
control
equations by inserting a # symbol. Everything following the # symbol in a
SEL
OGIC
control equation is treated as a comment. See Table 4.57 for this and
other Boolean and math operators and values.
When you combine several operators and operands within a single expression,
the SEL-700G evaluates the operators from left to right, starting with the
highest precedence operators and working down to the lowest precedence.
This means that if you write an equation with three AND operators, for
example SV01 AND SV02 AND SV03, each AND is evaluated from left to
right. If you substitute NOT SV04 for SV03 to make SV01 AND SV02 AND
NOT SV04, the device evaluates the NOT operation of SV04 first and uses the
result in subsequent evaluation of the expression.
Table 4.56
SEL
OGIC
Control Equation Operators (Listed in Operator
Precedence)
(Sheet 1 of 2)
Operator
Function
Function Type (Boolean
and/or Mathematical)
( )
parentheses
Boolean and Mathematical
(highest precedence)
–
negation
Mathematical
NOT
NOT
Boolean
R_TRIG
rising-edge trigger/detect
Boolean
F_TRIG
falling-edge trigger/detect
Boolean
*
/
multiply
divide
Mathematical
Summary of Contents for SEL-700G Series
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