Sel 411L - Table 14.26 Math Operator Summary; Table 14.27 Math Error Examples

P.14.29
Date Code 20151029 Protection Manual SEL-411L Relay
SELOGIC Control Equation Programming
SEL
OGIC Control Equation Operators
Parentheses
Use parentheses to control the order in which the relay evaluates math
operations within a math SEL
OGIC control equation. Also use parentheses to
group expressions that you use as arguments to function operators such as SIN
and COS. Include as many as 14 levels of nested parentheses in your math
SEL
OGIC control equation. Example 14.13 shows how parentheses affect the
operation and evaluation of math operations.
EXAMPLE 14.13 Using Parentheses in Math Equations
The free-form math SEL
OGIC control equations below show examples
of parentheses usage.
# Examples of parenthesis usage
AMV001 := AMV005 * (AMV004 + AMV003) # Calculate sum first, then
product
AMV002 := AMV010 * (AMV009 + (AMV016 / AMV015) ) # Nest parenthe-
ses
AMV003 := SIN (AMV037 + PMV42) # Group terms for a function
Math Error Detection
If a math operation results in an error, the relay turns on the math error bit,
MATHERR, in the Relay Word. A settings change or the STATUS SC
command resets this bit. For example, if you attempt to take the square root of
a negative number (SQRT –5), the math error bit will be asserted until you
clear the bit with a STATUS SC command or change settings.
Ta b l e 1 4 .26 M at h O p e ra to r Su m ma r y
Operator Description
( ) Parentheses
+, –, *, / Arithmetic
SQRT Square root
LN, EXP, LOG Natural logarithm, exponentiation of e, base 10 logarithm
COS, SIN, ACOS, ASIN Cosine, sine, arc cosine, arc sine
ABS Absolute value
CEIL Rounds to the nearest integer towards infinity
FLOOR Rounds to the nearest integer towards minus infinity
– Negation
Table 14.27 Math Error Examples
Example Value in PMV01 Type MATHERR
PMV01 := PMV02 / 0 0
a
Divide by zero Yes
PMV01 := LN ( 0 ) 0
a
a
Evaluation of expression results in an error and prevents storage of new result. In the
example, PMV01 remains 0. If the argument were a variable, PMV01 would contain the result
of the last evaluation when the argument is valid.
LN of 0 Yes
PMV01 := LN ( -1) 0
a
LN of negative number Yes
PMV01 := SQRT ( -1) 0
a
Square root of a negative
number
Yes