Advantages of STAR and DELTA connection in Induction Motor

We know that Induction Motor started with Star Connection but runs with Delta Connection using Star Delta Starter, But why? Sometimes this question is asked in a different way which is why the star delta starter is more preferable for the starting of an induction motor. In fact, the LT motors are generally delta connected but the HT motors are generally Star connected. So, Star and Delta connections both are used in Induction motors because of their own advantages. So let's discuss this in detail.

The Advantages of using Delta Connection in LT Motors

1. Generally, the 440V motors are called LT motors. As there is no requirement for very high insulation arrangements, we can easily give 440V across all windings using the delta connection.

2. Mainly LT motors are used where high starting torque is required. The high starting torque can be developed using only the delta connection because, in the delta connection, the voltage across each winding is root three times higher than the star connection.

3. There is no requirement for the arrangement of balancing voltage because, in a delta connection, the voltage across each winding is the same.

4. We know that in a delta connection, the line current is root three times greater than the phase current which is also an advantage of using a delta connection in an Induction Motor.

5. In Delta connection, Third Harmonics is eliminated because here the zero sequence current circulates through the delta-connected winding.

6. Delta connections require fewer winding turns and connections, making them simpler and more cost-effective to manufacture and install. 

The Advantages of using Star Connection in HT Motors

1.  We know that, in Star connection, the phase voltage is root three times lesser than the line voltage, so the voltage across each winding will be less. This is the main reason for using a star connection in HT motors.

2.  Star connection is generally used in HT motors, those motors are used where low starting torque is required. As the torque is proportional to the square of the voltage, so star connection is used because, in a star connection, the voltage across each winding is less.

3. As there is less voltage across each winding, therefore less insulation is required which decreases the cost or saves money.

4. Star-connected starters are more simple and cheaper than delta starters.

5. The star connection allows for the creation of a neutral point, which can be connected to the ground. This neutral point provides a reference point for zero potential that helps with voltage unbalance detection, earth fault detection and protection.

The induction Motor is started with STAR Connection and runs with Delta Connection

At the starting time, the induction motor draws 7 to 8 times higher current than the rated current so to reduce the starting current Star Delta Starter is used. As the star connection provides a low voltage across each winding, so the current will be less. For this reason, Induction Motor is started with a Star connection to reduce the starting current by reducing the voltage across windings.

Now, once the motor is started, the induction motor requires high torque to drive the heavy load. So in running conditions, a delta connection is used to develop high torque by providing a high voltage across windings.

For small motors, we can use Direct On Line(DOL) Starters but for big motors, we must use star-delta starters.

**It's important to note that the choice of motor connection (star or delta) can vary depending on specific requirements such as system design, and other factors. Engineering considerations, motor characteristics, voltage levels, load conditions, and the intended application all play a role in determining the appropriate connection configuration for a motor.**

Read Also:

• Why is Three Phase Induction Motor Self-Starting but Synchronous Motor not?
• Why is Alternator Armature Winding always connected in STAR?
• Why Capacitor is used in Single-phase Induction Motors?

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