A big advantage of A.C. transmission is the ability to easily change voltage by means of a transformer. As there are no moving parts maintenance is very low and efficiency very high ( typically 98%). A transformer consists of two insulated coils wound separately over a closed magnetic field, usually iron, of low reluctance. An alternating supply E1 acts across a coil called the primary, a voltage is induced in the secondary coil E2.

Details of a small transformer-the core is built up of stamped laminated sheets of silicon iron about 0.35 mm thick insulated from one another by a thin layer of paper or varnish. The purpose of laminating the core is to reduce the loss due to eddy currents induced by the alternating magnetic flux. The vertical portions of the yoke are called the 'limbs' and the horizontal portions are called the 'yokes'

Shell type

Auto transformer

Auto transformers are used in:

• Starting motors
• In power factor corrections with capacitance's.
• Incorporated in portable appliances such as radios.
  
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