07Level 3

Star-delta starter with timer

The motor starts in star, with less current, and after a few seconds switches to delta. A timer marks the change and a short pause prevents a short circuit between contactors.

Open in the simulator

The simulator is designed for computers (screens 1024 px or wider).

Virtual plant

Shown at rest. In the simulator the plant moves according to your program's outputs.

Inputs and outputs

Address	Name	Description
I0.0	START	Start push button (NO)
I0.1	STOP	Stop push button (NC: 1 at rest)
I0.2	OVERLOAD	Overload relay NC contact (driven by the plant: 0 = tripped)
Q0.0	K1_MAIN	Main contactor
Q0.1	K2_STAR	Star contactor
Q0.2	K3_DELTA	Delta contactor
T0	T_STAR	Time in star (5 s)
T1	T_GAP	Pause between star and delta (100 ms)
M0.0	GO_DELTA	Star and pause are over: connect delta

Program

Ladder diagram (LD)

Rung 1 — Main contactor with seal-in.
Rung 2 — 5 s in star and a 100 ms pause before delta.
Rung 3 — Star: until the time is over, interlocked with delta.
Rung 4 — Delta: after the pause, interlocked with star.

Structured text (ST)

(* Star-delta starter with timer — converted from Ladder *)

VAR
  T_STAR : TON;
  T_GAP : TON;
END_VAR

(* Rung 1: Main contactor with seal-in. *)
K1_MAIN := (START OR K1_MAIN) AND STOP AND OVERLOAD;

(* Rung 2: 5 s in star and a 100 ms pause before delta. *)
T_STAR(IN := K1_MAIN, PT := T#5s);
T_GAP(IN := T_STAR.Q, PT := T#100ms);
GO_DELTA := T_GAP.Q;

(* Rung 3: Star: until the time is over, interlocked with delta. *)
K2_STAR := K1_MAIN AND NOT T_STAR AND NOT K3_DELTA;

(* Rung 4: Delta: after the pause, interlocked with star. *)
K3_DELTA := K1_MAIN AND GO_DELTA AND NOT K2_STAR;

Instruction list (IL)

(* Star-delta starter with timer — converted from Ladder *)

VAR
  T_STAR : TON;
  T_GAP : TON;
END_VAR

(* Rung 1: Main contactor with seal-in. *)
  LD    START
  OR    K1_MAIN
  AND   STOP
  AND   OVERLOAD
  ST    K1_MAIN

(* Rung 2: 5 s in star and a 100 ms pause before delta. *)
  CAL   T_STAR(IN := K1_MAIN, PT := T#5s)
  CAL   T_GAP(IN := T_STAR.Q, PT := T#100ms)
  LD    T_GAP.Q
  ST    GO_DELTA

(* Rung 3: Star: until the time is over, interlocked with delta. *)
  LD    K1_MAIN
  ANDN  T_STAR
  ANDN  K3_DELTA
  ST    K2_STAR

(* Rung 4: Delta: after the pause, interlocked with star. *)
  LD    K1_MAIN
  AND   GO_DELTA
  ANDN  K2_STAR
  ST    K3_DELTA

Step by step

1Press ▶ Run (F5) and press START: K1_MAIN and K2_STAR close. See the starting current in the plant, much lower than with a direct start.
2After 5 s the T_STAR timer opens K2_STAR. After a 100 ms pause (T_GAP) K3_DELTA closes and the motor reaches its rated speed.
3The NC contacts of K2 and K3 on each other are an interlock: if both closed together there would be a short circuit. The pause lets the star contact really open before the delta contact closes.
4Try changing the star time to T#1s: the motor switches to delta at low speed and the current peak goes up.

Open in the simulator