Synchronous Generators(Alternators)

INTRODUCTION

An alternating voltage is generated in a single conductor or armature coil rotating in a uniform magnetic field with stationary field poles.An alternating voltage will also be generated in stationary armature conductors when the field poles.state past the conductors.Thus,we see that as long as there is a relative motion between the armature conductors and the field flux there will be a voltage generated in the armature conductors.In both the cases the wave shape of the voltage is a sine curve.

In d.c. generators,the field poles are stationary and the armature conductors rotate.The voltage generated in the armature conductors is of alternating nature.This generated alternating voltage is converted to a direct voltage at the brushes with the help of the commutator.

A.c. generators  are usually called alternators.They are also called synchronous generators.Rotating machines that rotate at a speed fixed by the supply frequency and the number of poles are called synchronous machines.

A Synchronous generator is a machine for converting mechanical power from a prime mover to ac electric power at a specific voltage and frequency.A synchronous motor is a synchronous machine that converts electric power to mechanical power.Synchronous generators are usually of  3-phase type because of the several advantage of 3-phase generation,transmission and distribution.Large synchronous generators are used to generated bulk power at thermal,hydro and nuclear power stations.Synchronous generators with power ratings of several hundred MVA are very commonly used in generating stations.The biggest size used in India has a rating of 500 MVA used in super-power thermal power stations.Synchronous generators are the primary sources of worlds electric power systems today.For bulk power generation, stators windings of synchronous generators are desidgned for voltages ranging from 6.6 kV to 33 kV.