Ladder Logic Programming in SEL RTAC
Key Takeaway
How to write Ladder Diagram programs in ACSELERATOR RTAC for substation automation — contacts, coils, timers, and practical breaker control and interlock examples.
Quick Answer
RTAC Ladder Diagram uses contacts and coils referencing RTAC BOOL tags, with timer (TON, TOF, TP) and counter (CTU, CTD) function blocks. Ladder is preferred for discrete control, interlocking, and Boolean sequencing in substation automation.
When to Use Ladder
Discrete control, breaker interlocks, alarm annunciation, Boolean sequencing. For complex calculations use ST; for analog processing use FBD.
RTAC Tag Access
All tags populated by protocol drivers (SEL protocol, DNP3, Modbus, IEC 61850) are directly accessible as contacts and coils by tag name.
Example: Breaker Failure Detection
Rung: [Trip_Coil_Energized] ---- [TON BF_Timer PT:T#133ms]
Rung: [BF_Timer.Q AND NOT Breaker_52A_Open] ---- [BF_Trip_Output]Example: Automatic Bus Transfer Interlock
Monitor bus voltage and source availability. Initiate transfer on source loss with permissive conditions verified.
Calling SEL Function Blocks
SEL power system blocks (POTT, BF, RECLOSE) appear as function block instances in Ladder.
Frequently Asked Questions
Set coil (S) on one rung sets a BOOL tag TRUE. Reset coil (R) on another rung resets it FALSE. Tag retains state between scans.
Yes. All tags from SEL protocol, DNP3, Modbus, and IEC 61850 drivers are accessible as contacts and coils by tag name.