Star Delta Starter Diagram

Here the circuit diagram of Star Delta Starter explained in detail. Here you will learn the connection of Star Delta Starter with Three-Phase Motor. The Power Circuit diagram and Control Circuit diagram of an Automatic Star Delta Starter are explained below. Let's understand the Star Delta Starter Diagram.

A star-delta starter is basically an electrical motor control circuit used for starting three-phase induction motors. It employs a combination of two motor winding configurations, known as the star and delta configurations, to reduce the starting current and provide a smooth transition during motor starting. The star-delta starter allows for a reduced starting current compared to direct-on-line starting. This is beneficial because starting a motor with a high current can cause voltage drops, and it puts a strain on the motor windings and power supply. By using the star-delta starter, the motor starts with reduced voltage and current, minimizing these issues.

We know that in Star Connection the Line Voltage is Root Three Times of Phase voltage. So we start the Motor with Star connection and after a small time when the Motor is Running, we connect the motor in Delta Connection.

So our main target is, at the starting time the motor windings should be connected in Star and then it should be connected in Delta.

Here a diagram of Three Phase Motor Stator Winding arrangement and connection is shown. First, see the below diagram carefully to easily understand the Star Delta Starter Diagram.

As you see in the above figure, Three-phase Motor has three windings which are placed at 120 degrees to each other. All terminals are brought to the outside. In the above diagram, I have shown also how we can connect the windings in Star and Delta.

Now we connect the motor windings in Star and Delta for starting and running of the Motor. Actually, the total arrangement or circuit of connecting the motor windings in Star and Delta with a small time delay is called Star Delta Starter.

Here both Power and Control Circuit diagrams of an Automatic Star Delta Starter are explained below.

Star Delta Starter Power Circuit Diagram:

You can see in the below figure, I have shown the Star Delta Starter Connection with a Three Phase Motor.

First, a Main switch or MCB or MCCB is connected to give the power supply to the Circuit.

Then a Thermal Overload Relay is connected for the protection purpose. The Thermal Over Load relay will trip the circuit if a short circuit or overload fault occurs in the Motor.

In the Power Circuit of Star Delta Starter, three contractors are used. One is the main Contactor which will be always ON after starting the motor. The other Contactors are Star Contactor and Delta Contactor.

The star contactor is used to make Star connection. Only during the starting time, the Star Contactor remain ON after a small time it will be OFF and the Delta Contactor will be ON.

Delta Contactor is used to make the delta connection. It will be Turn ON after turning OFF the Star contactor and remain ON until we stop the Total operation.

Don't Confuse with the terms Star Contactor and Delta Contactor. They are not any special types of Contactor. Here all contactors are the same type of contactor. Here the terms Delta Contactor and Star contactor are used according to their operation.

Star Delta Starter Control Circuit Diagram:

Here you can see the Control Circuit Diagram of Automatic Star Delta Starter.

As you see in the above Star Delta Starter Diagram,

First, an NC push Button switch is connected to Stop the operation.

Next,  the circuit goes through the NC terminals of the Thermal Over Load Relay. When the fault occurs the thermal overload relay will trip the circuit.

Next, a NO Push Button switch is connected to start the operation.

The NO terminals of the main Contactor is connected across the NO Push Button switch for Holding. That means when the NO push button switch is OFF, the circuit will remain ON.

The Star Contactor is Connected with the NC terminal of the Timer and the Delta Contactor is connected with the NO terminal of the Timer.
So at the starting time, the Star contactor will be turned ON. After a small time(which is to be set manually) the NC of the Timer will be NO and NO will be NC so the Delta contactor will be turned ON and remain ON until we push NC Push Button Switch for Stop.

So, this was the total concept of the Star Delta Starter Diagram.