Three phase circuits

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Three Phase Circuits

When there are multiple armature windings, which are displaced from other by equal angles, generating multiple independent voltage waves (same as the number of armature windings separated by equal angles), they form a polyphase system. Such a system in which three independent voltage waves are produced is known as a three phase system.

Generation, transmission and utilization of power are largely carried out by three phase systems.

Advantages of three phase systems over single phase systems

For given frame size, three phase system has more output than a single phase system

Three phase system has uniform torque, single phase system has pulsating torque (why? - need to find out later)

Work in parallel w/o difficulty

Require smaller amount of conductor material for transferring same amount of power as in single phase.

Self starting

Cheaper, efficient.

Three Phase AC Generation

Three identical coils are placed at 120°. Rotated in uniform magnetic field. Identical coils rotating in same magnetic field have same voltages induced of same magnitude and frequency.

Vr= VmSin(wt)

Vy=VmSin(wt-120°)

Vb=VmSin(wt-240°)

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