Schweitzer Engineering Laboratories SEL-421-4 - Page 1186

13.20
SEL-400 Series Relays Instruction Manual Date Code 20171006
SELOGIC Control Equation Programming
SEL
OGIC Control Equation Elements
A sequencing timer counts time by incrementing the Elapsed Time when
SEL
OGIC control equation execution reaches the Input equation if the Reset is off
and the Input is on. The Output turns on when the Elapsed Time reaches or
exceeds the Preset Time. Whenever the Reset is on, the relay sets the Output to
zero, then clears the Elapsed Time, and stops accumulating time (even if Input is on).
Figure 13.8 is a timing diagram for typical sequencing timer operation.
Timers in protection programming operate in cycles, while timers in automation
programming operate in seconds. As with sequencing timers, operation depends
on the logic processing interval. For example, in most SEL-400 series relays the
logic processing interval is 1/8 cycle, so the relay effectively rounds up all opera-
tion to the nearest 0.125 cycles. With automation programming, the execution
interval depends on the amount of automation programming. Determine the aver-
age automation execution interval with the STATUS S command.
Table 13.12 Sequencing Timer Parameters
Type Item Description Setting
Name
Examples
Input Input Value that the relay
times
Boolean SELOGIC control
equation setting
PST01IN
AST07IN
Input Preset
Time
Time the input must be
on before the output
turns on
Time value. Protection uses
cycles, while automation uses
seconds.
PST01PT
AST07PT
Input Reset Timer reset Boolean SEL
OGIC control
equation setting
PST01R
AST07R
Output Elapsed
Time
Time accumulated since
the last reset
Value for math SEL
OGIC con-
trol equations. Protection
uses cycles, while automation
uses seconds.
PST01ET
AST07ET
Output Output Timer output Value for Boolean SEL
OGIC
control equations
PST01Q
AST07Q
Figure 13.8 Sequencing Timer Timing Diagram
Elapsed Time
Increases While
Input Is On
Elapsed Time
Does Not Reset
When Input Is Off
Elapsed Time Reaches
Preset Value
Elapsed Time
PST01ET
Input
PST01IN
Reset
PST01R
Output
PST01Q
Preset Value
PST01PT