Parallel operation of single phase transformer, Uses of auto transformers

Parallel operation of single phase transformer:

Single_Phase Transformer 

1) Primary winding of the transformer should be suitable for the supply system voltage and frequency

2) The transformers should be properly connected with regard to polarity.

3) the voltage ratings of both primary and secondary should be identical. In other words the transformers should have the same turn ratio.

4) the percentage impedance should be equal in magnitude and have the same X/R ratio.

5) with transformer having different KVA rating, the equivalent impedance should be inversely proportional to the individual KVA rating.

Uses of auto transformers:

1) to give small boost to a distribution cable to correct voltage drop.

2 ) As auto transformer to give up to 50 to 60% of full voltage to an induction motor out during starting. 

3) As furnace transformer.

4) As interconnecting transformer in high voltage system.

5) in control equipment for single phase and 3 phase electrical locomotives.