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AC generator vs DC generator-Difference between AC generator and DC generator

This page on AC generator vs DC generator describes basic difference between AC generator and DC generator types.

All electrical generators whether ac or dc, depend upon principle of magnetic induction regardless of their size. In a dc generator, the armature is always the rotor. In alternators, the armature may be either the rotor or stator.

AC Generator

AC generator types

It is a machine which converts mechanical energy into AC electrical energy. It is known as AC generator.
It works on the principle of electromagnetic induction: "Whenever a conductor cuts the magnetic lines of force, an e.m.f. is induced in it. "

As shown in the figure-1 there are two types of AC generators viz. rotating armature alternator and rotating field alternator. Here e.m.f. or generated AC voltage by alternator is supplied to the external circuit using two slip rings and two brushes.

The machine which converts mechanical energy into DC electrical energy is known as AC Dynamo. EMF generated by dynamo is supplied to external circuit in the form of DC voltage using commutator and two brushes.
Dynamo efficiency is expressed as follows:
Dynamo efficiency = (Output electrical power/Input mechanical power) x 100 %

DC Generator

DC generator

As we know elementary generator consists of a single coil rotating in magnetic field. It produces AC voltage. A basic DC generator is constructed when slip rings of elementary generator is replaced with two piece commutator. This changes output voltage to pulsating DC voltage. This is depicted in the figure-2.

A Multiple coil armature decreases ripple and increases output voltage of the DC generator.

Following table mentions comparison between these generator types with respect to various features.

Features AC Generator DC Generator
Function Generates AC output. Generates DC output.
Output connections In the alternator used in ac generator, the generated ac is brought to the load unchanged by means of slip rings. In the dc generator, the emf generated in the armature windings is converted from ac to dc by means of the commutator.
Types or classifications Types of AC generators are rotating armature alternator and rotating field alternator. Single phase AC generator produces 25 KW or less. Single phase generates power at specific voltage. Polyphase generates two or more AC voltages usually two, three or six phases. They are classified into excitation of their fields viz. permanent magnet type, separately excited type, self excited type, shunt/series type, compound type
Advantages • It is simple in construction.
• More powerful three phase generators can be constructed.
• It is very easy to distribute AC voltage with the help of transformers.
• Lots of devices depend on DC current for their operation.
• At given voltage, DC current is powerful compare to equivalent AC current.
Disadvantages • The electricity Grid requires fine co-ordination to ensure that all the generators are in phase with each other.
• AC current is more dangerous compare to equivalent DC current due to electric shock.
• It will have more complex construction with split ring commutator.
• Sparking occurs in gap of commutator which wastes energy.
• It is more difficult to distribute DC in efficient manner.


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