Here is the answer to one of the follower of Online Electrical Engineering.Her question is "I need a auto transformer for 2hp motor 380 volts 3phase.Now my problem is my line is 220volts 1phase.What should be the auto transformer capacity?"
Autotransformer is not similar to the power transformer.Power transformer works on the principle of mutual induction whereas autotransformer works on the principle of self induction.Autotransformer has only one winding and the same winding acts as primary winding and secondary winding.Also it is not electrically isolated where as in power transformer windings are electrically isolated.
Autotransformer will have one tapping common to both source and load side winding.The other tapping will be connected to the source on primary side winding.Multiple tappings are provided on secondary side winding to have multiple voltage outputs. Autotransformer is usually a step down transformer and can be used to provide the supply voltage to the electrical appliances/electrical instruments.
There are two types of autotransformers based on the phase.Single phase autotransformers and three phase autotransformers are the types of autotransformers.Single phase autotransformer can be used to provide supply to the single phase devices.Three phase autotransformers can be used to supply single/three phase electrical devices but the single phase autotransformer cannot be used to supply the three phase electrical devices.
