What is DC generator?
A direct current generator or DC Generator is an electrical machine that converts mechanical energy into electrical energy in the direct current domain. This energy conversion is based on the principle of dynamically induced emf generation. In this article, We will study the basic construction and operation of a DC generator.
Types of DC generator
DC generators are classified on the basis of the field excitation system. According to the field excitation system dc generators are classified into two categories
- Self Excited DC Generator
- Separately Excited DC Generator
Self Excited DC Generator
In this DC generator, some fractional parts of the induced current are fed back to the field winding for the production of magnetic flux. When initially generator starts emf induce due to residual magnetic flux. Whenever emf is induced in the armature, current starts to flow in the field winding that strengthens the magnetic flux due to this magnitude of induced emf increases. Self-excited DC generators are classified into three categories and these are :
- Series wound DC Generator
- Shunt-wound DC Generator
- Compound wound DC Generator
Separately Excited DC Generator
In this DC generator, the field winding is connected to an external source of DC Current. Magnetic flux can be controlled externally.
Working Principle of DC generator
The working principle of the dc generator is based on faraday's law of electromagnetic induction. According to Faraday's law of electromagnetic induction, whenever there is a relative motion between the magnetic field and a conductor, then an emf is induced in the conductor. The magnitude of the induced emf can be calculated from the DC generator emf equation. If the conductor has a closed path, the current will flow through that path. In a DC generator, the coil creates an electromagnetic field and the armature conductors rotate in the field by an external mover. As a result, an emf is produced which causes an electromagnetic field to be produced in the armature conductors. The direction of the induced current can be determined by Fleming's right-hand law.
According to Fleming's right-hand law, the direction of the current changes whenever the direction of motion of the conductor changes. Note that the steering wheel rotates clockwise as the driver's left side moves up. When the arm rotates halfway, the direction of travel of the conductor will be reversed. Therefore, the direction of the current in each armature conductor will be reversed. If you look at the figure above, you will know that the direction that moves the current changes in the direction of the armature. But in a split ring circuit, the connection of the armature conductors also rotates as the current changes. So we get a unidirectional current from the node.
Construction of DC Generator
The Construction detail of the DC generator has been given below figure. Different parts of DC generators have been shown in the figure given below:
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| Image Source:https://www.electricaleasy.com/2022/09/construction-and-working-of-dc-generator.html |
Armature Conductor
Armature conductors are fine copper wires that are kept inside the slot of the armature. When large numbers of conductors are placed inside the armature slot then it is simply known as armature winding. The armature conductors are insulated from each other and also from the armature core. Armature winding can be wound by one of the two methods; lap winding or wave winding. Double-layer lap or wave windings are generally used. A double layer winding means that each armature slot will carry two different coils.
Armature
The armature is the part of the DC machine (Generator or Motor) in which electromotive force(EMF) gets induced. The armature may be either rotating parts or static parts but in most cases, the armature is a rotating part of a DC machine.
Yoke
The outer part or frame of a dc generator is known as Yoke. it is made up of high-grade steel or cast iron. it provides mechanical support to the dc generator.
Poles and Pole shoes
Poles and pole shoes are inner parts of dc motors, these are connected with Yoke by either bolts or welding. Poles carry field winding and pole shoes are fastened to them. it performs two tasks inside the yoke(a) it supports the field coil and (b) distributed magnetic flux uniformly.
Field Winding
these are copper conductors placed on each pole of the dc generator. Each conductor of the pole is connected in series and forms field winding. When this winding is connected to an external source of dc current then each pole of the dc generator becomes magnet of alternate south and north pole.
Commutator
It is a part of the dc generator where armature conductors are connected together. the function of the commutator is to collect the current induced inside each armature conductor. In the case of a DC motor, it is used to provide dc current in the armature conductor. A commutator consists of a set of copper segments that are insulated from each other. The number of segments is equal to the number of armature coils. Each segment is connected to an armature coil and the commutator is fixed to the shaft.
Brush or Carbon Brush
It is a special part of the dc generator that provides a path for collected current in the commutator to the external circuit. it is made up of either pure carbon or graphite. it is physically connected with a shaft and makes contact while the shaft is rotating.