Star Delta Forward Reverse Starter with PLC Ladder Logic Conversion

Table of Contents

Star Delta Forward Reverse Starter

We all know about the star-delta starter and how it works? But I have questioned many times about the star-delta starter with forward-reverse function. So, today in this blog, We are going to see how the forward-reverse function works with a star-delta starter.

Star Delta Forward Reverse starter can be achieved in two ways. In this blog, we are going to see these two methods.

Method#1

In this method1, we are going to add forward and reverse contactors on the main supply line above the star-delta starter. You can find the control and power drawing of this method.

Control Drawing

STEP1 ⇒ When we press the Start Fwd pushbutton, it will start Fwd contactor. Likewise, when we press the Start Rev pushbutton it will start Rev contactor.

There is an interlock for the safety purpose between Fwd and Rev. If one of the two contactors is ON, it will not let starts another contactor. If we want to start the motor in another direction then we have to stop the starter first.

STEP2 ⇒ As soon as the Fwd or Rev contactor starts, it will activate the Timer as well as Star and Main contactors. The motor will run now in the STAR connection for the preset time, till that it will achieve 75-80% of the full load speed. Star contactor will stop after the preset time of the Timer.

STEP3 ⇒ This is the transition stat when only the Main contactor remains ON. Both the Star and Delta contactor is OFF in this stat. There is a voltage across only one end of the motor windings. The rotor is still rotating.

STEP4 ⇒ After the preset time, the Delta contactor starts and the motor is running with the full voltage at the full load speed with the full torque.

Power Drawing

Here in this power drawing, you can find both the forward and reverse stats.

Forward Stat

In this stat, we have applied a normal phase sequence R, Y, B to the motor windings.

Reverse Stat

In this stat, we have changed the phase sequence from R, Y, B to the B, Y, R using Rev contactor to the motor windings.

PLC Ladder Logic

You can see the ladder logic conversion of the method1. This is completely for your reference if you want to convert the control wiring with PLC ladder logic.

Method#2

In this method2, we have different contactors for both forward and reverse directions such as Fwd Main, Rev Main, Fwd Delta, and Rev Delta. You can find the control and power drawing of this method.

Control Drawing

STEP1 ⇒ When we press the Start Fwd pushbutton, it will start Fwd Main contactor. Likewise, when we press the Start Rev pushbutton it will start Rev Main contactor.

There is an interlock for the safety purpose between Fwd Main and Rev Main. If one of the two contactors is ON, it will not let starts another contactor. If we want to start the motor in another direction then we have to stop the starter first.

STEP2 ⇒ As soon as the Fwd Main or Rev Main contactor starts, it will activate the Timer as well as Star contactor. The motor will run now in the STAR connection for the preset time, till that it will achieve 75-80% of the full load speed. Star contactor will stop after the preset time of the Timer.

STEP3 ⇒ This is the transition stat when only the Fwd Main/Rev Main contactor remains ON. Both the Star and Fwd Delta/Rev Delta contactor is OFF in this stat. There is a voltage across only one end of the motor windings. The rotor is still rotating.

STEP4 ⇒ After the preset time, the Fwd Delta starts if the command is given from the Start Fwd pushbutton or Rev Delta starts if the command is given from the Start Rev pushbutton.

There is also an interlock between the Fwd Delta and Rev Delta contactors. Now the motor is running with the full voltage at the full load speed with the full torque.

Power Drawing

Forward Stat

In this stat, we have applied a normal phase sequence R, Y, B to the motor windings using Fwd Main and Fwd Delta contactors.

Reverse Stat

In this stat, we have changed the phase sequence from R, Y, B to the B, Y, R using Rev Main and Rev Delta contactor to the motor windings.

PLC Ladder Logic

You can see the ladder logic conversion of the method2. This is completely for your reference if you want to convert the control wiring with PLC ladder logic.

I hope you like this article about star delta forward reverse starter, if you would like this article then please share it with your friends and colleagues and comment down below about your feedback.

You can read more articles about Electrical and you can also find books that boost your knowledge in the field of Instrumentation ⇒