What is Alternator:
Generally Alternator also called AC generator. Alternator is a machine used to convert the mechanical power into electrical AC power with specific voltage and frequency. Alternator is having stationary armature conductor and rotating magnetic field. the rotating mechanical source is connected to shaft of the alternator. shaft is connected with rotor of the alternator. whenever the shaft rotated then rotor also rotated. then the rotor coil is induced the current in the stator armature coil. the output current is collect from the stator output terminal.
so here we will see briefly about how the alternator is working and how its producing voltage.
How Alternator working:
The working of alternator is similar to the generator. as per the construction the alternator and generator is different. the below diagram shows the construction of alternator.
stator windings are star connected and stator windings placed to pole core. the stator core are laminated to reduce the eddy current and hysteresis losses. Normally the rotor having salient pole rotor type. the salient pole rotor having 10 to 20 numbers poles to reduced the speed of the rotor.
F = PN/120
Rotor winding is connected to DC source by slip ring or small dc generator is fitted on the same prime mover. this type of alternator is called self excited alternator others called separately excited alternator.
when ever the mechanical source starts rotated then rotor also start rotate. the rotor get excited by external dc source. so the rotor winding is produced the rotating induced emf. according to faradays law of electromagnetic induction principle. the rotor winding is induced the current in the stator armature coil. finally alternator producing 3 phase supply from the stator armature terminal.
Alternator output Vs load:
The output of the alternator is varying with changing the connecting load. when ever the load increase the output voltage of the alternator will be decrease. so the maintaining the alternator output voltage constant by adjusting the field current in the rotor. that could be done by automatic voltage regulator (AVR).
If the terminal voltage is below the desired level then AVR is increase the field current. it means it increase the alternator terminal voltage. if terminal voltage is above the desired level then AVR is decrease the field current. so the terminal voltage also decreased.