Electrical Engineering ⇒ Topic : advantages and disadvantages of auto transformers

Advantages :

1. Voltage is reduced by transformation and not by dropping the voltage in resistors,and therefore, the current and power drawn from the supply mains are also reduced in comparison to resistor starting.
2. Availability of highest torque per ampere of supply current.
3. Adjustment of starting voltage by selection of proper tap on the auto-transformer.
4. The method is suitable for long starting periods..
5. Motor current larger than supply current.

Closed transition starting.

Disadvantages :

Low power factor.

Higher cost in case of lower output rating motors.

• This method can be used for starting of star-connected as well as delta-connected motors.
• This method is often employed for starting of large cage motors (rating exceeding 20 κW)