Question

Draw neat diagram of star-delta starter for three phase induction motor.

Answer 1

I can't draw diagrams, but I can describe the layout for a star-delta starter:

1. **Main Components:**
   - **Contactor K1 (Star Contact)**: Controls the star connection.
   - **Contactor K2 (Delta Contact)**: Controls the delta connection.
   - **Overload Relay**: Protects the motor from overloads.
   - **Timer**: Switches from star to delta after a set time.

2. **Connections:**
   - **Three-Phase Supply**: Connected to the L1, L2, and L3 terminals.
   - **Motor Terminals**: U1, V1, W1 are connected to the star point. U2, V2, W2 are connected to the delta configuration.
   - **Contactor K1**: Connects the motor terminals to the star point. K1’s NO (Normally Open) contacts are used.
   - **Contactor K2**: Connects the motor terminals to the delta configuration. K2’s NO contacts are used.
   - **Overload Relay**: Connected in series with the contactors to protect the motor.
   - **Timer**: Sets the duration for which the motor runs in star configuration before switching to delta.

In operation, the motor initially starts in star configuration to reduce the inrush current, and after a preset time, the timer switches the contactors to connect the motor in delta configuration for normal operation.

Answer 2

A Star-Delta starter is a common method used to reduce the starting current of a three-phase induction motor. It involves starting the motor in a star configuration and then switching to a delta configuration once the motor reaches a certain speed. Here’s a detailed explanation and diagram of a Star-Delta starter:

### **Diagram of Star-Delta Starter**

Here's a simplified explanation of the diagram components:

1. **Three-Phase Power Supply (L1, L2, L3)**: This provides the electrical power to the motor.
2. **Star-Delta Contactor**: This consists of three contactors:
   - **K1 (Star Contactor)**: Connects the motor windings in a star configuration.
   - **K2 (Delta Contactor)**: Connects the motor windings in a delta configuration.
   - **K3 (Main Contactor)**: Connects the motor to the power supply in both configurations.
3. **Overload Relay (OL)**: Protects the motor from overheating by disconnecting it if it draws too much current.
4. **Timer (T)**: Controls the time the motor remains in the star configuration before switching to the delta configuration.
5. **Start and Stop Push Buttons**: Used to start and stop the motor manually.
6. **Control Circuit**: Includes wiring and connections for controlling the contactors and timer.

### **Detailed Diagram**

Here's how the components are connected:

1. **Power Supply to Main Contactor (K3)**:
   - Connect the three-phase power supply lines (L1, L2, L3) to the main contactor K3.

2. **Main Contactor to Star and Delta Contactors**:
   - The output of the main contactor K3 connects to both the star contactor K1 and the delta contactor K2.

3. **Star-Delta Connection to Motor**:
   - **Star Configuration**: Connect the output of the star contactor K1 to the motor windings such that they form a star connection. This is achieved by connecting one end of each winding to a common point (neutral).
   - **Delta Configuration**: Connect the output of the delta contactor K2 to the motor windings such that they form a delta connection. Each winding is connected in a loop.

4. **Overload Relay (OL)**:
   - Connect the overload relay in series with the main contactor K3 to protect the motor from excessive current.

5. **Timer (T)**:
   - The timer controls the duration of the star configuration. It is connected to the star contactor K1 and ensures that after the preset time, the star contactor is deactivated and the delta contactor is activated.

6. **Start and Stop Push Buttons**:
   - The start push button is connected to the coil of the main contactor K3 and the timer. The stop push button is connected in series with the start push button to break the circuit and stop the motor.

### **Diagram Illustration**

```
          L1
           |
          [K3]
           |
          [OL]
           |
          [K1] ----> (To Motor - Star Configuration)
           |
           |
          [T] ----> (Timer to delay switch to Delta)
           |
          [K2] ----> (To Motor - Delta Configuration)
           |
          L2
           |
          L3
```

### **Operation**

1. **Starting**:
   - When the start button is pressed, the main contactor K3 is energized, connecting the motor to the power supply.
   - At this moment, the star contactor K1 is energized, connecting the motor windings in a star configuration. This reduces the starting current and torque.

2. **Transition**:
   - After the timer T elapses (usually set for a few seconds), the star contactor K1 is de-energized, and the delta contactor K2 is energized.
   - This switches the motor windings to a delta configuration, allowing the motor to run at full speed and torque.

3. **Stopping**:
   - Pressing the stop button de-energizes the main contactor K3, cutting off power to the motor and stopping it.

This diagram and description should help in understanding the Star-Delta starting method for three-phase induction motors.