Structured Text Programming in SEL RTAC

Quick Answer

RTAC Structured Text uses IEC 61131-3 syntax with RTAC-specific tag access. ST is preferred for complex calculations, state machines, and data quality handling. Access tags by name, check quality before using values.

Tag Access

// Read a tag value
currentIA := SUB1_SEL351_FDR1_IA.value;
// Check quality before using
IF SUB1_SEL351_FDR1_IA.quality = QUALITY#GOOD THEN
    // Use the value
END_IF;

Examples

// MVA and power factor calculation
MVA := SQRT(MW*MW + MVAR*MVAR);
IF MVA > 0.0 THEN PF := MW / MVA; ELSE PF := 0.0; END_IF;

// State machine for breaker sequence
CASE SequenceStep OF
    0: IF TransferCommand THEN SequenceStep := 10; END_IF;
    10: OpenBreaker1 := TRUE;
        IF Breaker1_Open THEN SequenceStep := 20; END_IF;
    20: CloseBreaker2 := TRUE;
        IF Breaker2_Closed THEN SequenceStep := 0; END_IF;
END_CASE;

For cross-platform ST comparison, see Allen-Bradley ST and IDEC WindLDR ST.