-Debraj Das(130370111011)

-Deepak Singh(130370111012)

In power stations, 3-Φ AC generator is used to produced 3-Φ voltage with low magnitude. This low magnitude of voltage is increased by using power transformer.

The machine which generates 3-Φ electric power from the mechanical power is called an alternator or synchronous generator. The shaft of the generator is coupled with mechanical turbine. The turbine may be gas, steam or water.

A synchronous machine with no-load is called asynchronous condenser or dynamic capacitor (used to correct the power factor).

Stator

The stator is the stationary part and is made of thin laminations of highly permeable steel to reduce losses.

The stator has ample number of slots in its inner periphery for stator winding.

The conductors are placed in the slots in a suitable way.The ends of theconductors are connected either in Υ or Δ to form the balanced 3 -Φwinding.

Rotor

It is the inner part of the alternator.It contains the field windings which are energized by direct current from the separate dc source.

Rotor winding is initially energized by a separate dc source.

A dc field current flows through the rotor field winding that establishes a flux in the air-gap which does not vary with time.

A rotating field of constant magnitude is produced in the air-gap when the rotor rotates due to a primemover.

The stator conductors are cut by this rotating flux, so that a voltage is induced in the armature conductors. If the rotor rotates continuously,then 3-Φ A C voltag e will be induced in the armature conductors.

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With reference to fig, the two conductors AB and CD alongwiththeir end connections constitute one coil of the armature winding. The coil may be single turn or multi-turn coil. A single turn coil will have two conductors.

The pitch factor is defined as the ratio of voltages generated by the short pitch winding to that which is generated in the full pitch winding.

Kp= (voltage induced in the short pitch coil)/(voltage induced in the full pitch coil)

Let the rms value of the coil side voltage is Ecsandthe resultant coil voltage is Ecr.

For full pitch winding:Ecr=2Ecs

For short pitch winding:Ecr=2Ecscos( 2/ץ)

Finally the pitch factor becomes,kp=cos( 2/ץ)