Schweitzer Engineering Laboratories SEL-421-4, Instruction Manual

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13.21
Date Code 20171006 Instruction Manual SEL-400 Series Relays
SEL
OGIC
Control Equation Programming
SEL
OGIC
Control Equation Elements
The automation timers operate using a real time clock. Each time the relay evalu-
ates the Input (AST
nn IN) the relay adds the elapsed time since the last execution
to the Elapsed Time (AST nn ET). The accuracy of the timer in stopping and start-
ing when the input of the timer turns on averages half an automation execution
cycle. If you change automation freeform programming, you must also check the
new automation average execution cycle to verify that you will obtain satisfac-
tory accuracy for your application.
Example 13.8 describes typical timer pro-
gramming and describes the resulting operation.
In freeform programming, the relay evaluates the timer at the timer Input
SEL
OGIC
control equation (PST nn IN or AST nn IN). If you enter an expression
for the timer Reset (PST nn R or AST nn R) or Preset Time (PST nn PT or AST nn PT),
the values for Reset and Preset Time that the relay uses are the last values that the
relay calculates before the input SEL
OGIC
control equation calculation. Because
the relay uses the last values for Reset and Preset Time value in this manner, we
recommend for most applications that you enter the Preset Time, Reset, and Input
statements together in the order shown in Example 3.8. You can view the current
state of the timer by assigning the elapsed time output of the sequencing timer to
a math variable.
Example 13.8 shows how you would assign the elapsed time out-
put for automation sequence timer AST01 to automation math variable AMV256.
To see the elapsed time value, issue the
MET AMV command to display the val-
ues of the automation math variables. Likewise, you can assign the elapsed time
output of a protection sequence timer to a protection math variable.
The elapsed time output is stored in volatile memory. Elapsed time resets to zero
for both protection and automation sequential timers when relay power cycles,
you change settings or settings groups, or you perform any function that reboots
the relay.
Example 13.8 Automation Sequencing Timer Programming
The equations below are an example of programming for an automation
sequencing timer, AST01. Each timer input is programmed as a separate
statement in automation SEL
OGIC
control equation programming.
# Example programming of sequencing timer to time Input IN101 and IN102
AST01PT := 7.5 # Timer Preset Time of 7.5 seconds
AST01R := RB03 # Reset timer when RB03 turns on
AST01IN := IN101 AND IN102 # Timing time when IN101 and IN102
are on
ASV001 := AST01Q # ASV001 tracks output of timer
AMV256 := AST01ET # AMV256 tracks timing progress
In this example, timer AST01 times the quantity IN101 AND IN102 and
turns on when the total time reaches 7.5 seconds. If the Input, AST01IN, is
on for approximately 1 second every minute, the Output, AST01Q, will turn
on during the eighth minute, when the accumulated elapsed time exceeds 7.5
seconds.