Electrical Machines

Electrical Machines
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1.      Single phase transformer – definition, working principle, e.m.f. equation, ampere turns relation, leakage reactance, equivalent circuit and vector diagram, parameters of equivalent circuit, voltages regulation, efficiency, parallel operation, Auto-Transformer.

It is as static device which transform electrical energy from one ac circuit to another without change in frequency and ideally power should also not change. 

       ·         Step-Up Transformer- receives electrical power at lower voltage level and delivers at a higher voltage level.

       ·         Step-Down Transformer – receives electrical power at higher voltage level and delivers at lower voltage level.

·        ·        It has no rotating parts; therefore, require less maintenance and provide higher efficiency compared to other electrical equipments.

Working Principle
It works based on the principle that energy may be efficiently transferred by induction form one set of coils to another by means of a varying magnetic flux, provided that both set of coils are on a common magnetic circuit. 
      ·         Electro-motive forces are induced due to change in flux linkages. 

      ·        In the generator, the flux is substantially constant in magnitude. The flux linking the armature is changed by the relative mechanical motion of the flux coils.

In the transformer, the coils (winding) and the magnetic circuit (ferromagnetic core) are all stationary refer figure given below.  Due to alternating supply which sets up changing flux inside the core the emf’s are induced by change in magnetic flux with time as illustrated .

Referring to above diagram,  an a.c. voltage is applied to the primary winding “P”. As this winding is linked with an iron core, its m.m.f. produces an alternating flux Φ in the core. This alternating flux links the turns of the winding “S”.  As this flux is alternating it induces in the winding “S” an e.m.f. of same frequency as the flux. Because of this induced e.m.f. the secondary winding is capable of delivering current and energy. the energy therefore is transferred from P, the primary to S, the secondary, by means of magnetic flux in a transformer, either winding may be the primary other being the secondary, depending up on which winding receives and which deliver energy .  



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