Brief insight on Synchronous Alternator theory & operation.

Alternator Theory: We can understand alternator operating principle in step by step.A basic alternator needs two things- a conductor & a magnetic field.When the conductor and magnetic field are in relative motion and magnetic filed cuts conductor ( not in parallel position ) then Alternating current will be produced in conductor.

Synchronous Speed of an Alternator:

The output frequency of alternator voltage depends upon the speed of rotation of the rotor and the number of poles. The faster the speed, the higher the frequency. The lower the speed, the lower the frequency. The more poles there are on the rotor, the higher the frequency is for a given speed.When a rotor has rotated through an angle such that two adjacent rotor poles (a north and a south pole) have passed one winding, the voltage induced in that winding will have varied through one complete cycle.

For a given frequency, the more pairs of poles there are, the lower the speed of rotation. As the number of pole in an alternator is even fixed number like 2,4,6 …40 ,the speed corresponding to a certain frequency is called synchronous speed for that frequency.

Speed, Pole and frequency inter relation:

N=120f/PN=Speed.F=Frequency.P=Pole.

Frequency regulation of an alternator
Frequency regulation of an alternator

Main parts of a synchronous AVK brand Alternator.

Click on the image to view full size.

main parts of a synchronous generator.
Main parts of a synchronous generator

Synchronous speeds of alternator for different pole and frequency:

synchronous speed of an alternator
This are the list of different synchronous speed of an alternator with pole and frequency.

Instrument transformers in a typical high range Alternator set.

Instrument transformers like Current transformers and Potential transformers are used to measure current and voltage for protection and measurement. Here is the list of instrument transformers that are used in the head section of high range Alternator.


Current transformer– For parallel operation, For short circuit excitation power on each phase, For measuring and protection.Voltage transformer for excitation power and Actual value measuring. Below is the cross sectional view of ABB alternator with instrument transformers in the head section.

instrument transformers in a typical alternator

One thought on “Brief insight on Synchronous Alternator theory & operation.”

  1. excitation system of LT 415 V alternator of AVK make for ships. explanation on mounting, function, maintenance, servicing , startingprecaution etc.

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