Generators either work on the principle of DC or AC, and different kinds of generators serve different purposes. In order to distinguish DC generators from AC generators, you need to be aware of certain aspects regarding them, such as their working, definition, parts of the generator and their working principle.
DC Generators are electric generators that convert mechanical energy into direct current. Direct Current is the unidirectional flow of the electric charge.
Here, we have elaborated on the concept and working of DC generator.
Faraday’s Law of Induction in a DC Generator
It is important to refresh Faraday’s Law of Induction, which acts as the working principle for electric motors, solenoids, transformers, inductors and working of generators for both AC and DC.
Faradays performed a series of experiments that helped him to conclude two basic laws of electromagnetic induction:
- First law of electromagnetic induction: The first law of electromagnetism shows how a magnetic field will interact with an electric circuit to produce an electromotive force (EMF).
In other words, a change in magnetic flux linked to a coil will generate an electromotive force (EMF) across a coil. And if there is no change in the magnetic flux, there will be no generation of electromotive force (EMF).
- Second law of electromagnetic induction: It states that the extent of EMF generated in the coil is equal to the rate of change of flux that linkages with the coil. EMF is proportional to the product of the number of turns in the coil and flux associated with the coil.
It can be represented as below:
EMF = -N(dϕB/dt)
Where N= Number of turns
ϕB = magnetic flux (BA)
B = external magnetic field
A = area of the coil
As per Lenz’s law, a negative sign shows that EMF induced always oppose the change in flux.
From the above equation, we can conclude by increasing the number of turns in the coil or by increasing the external magnetic field, we can increase the electromotive force (EMF).
DC GENERATORS
Electric generators are machines that generate electric currents. They utilise mechanical energy to convert it into electrical energy. There are various examples where mechanical energy is utilised to produce electricity, such as wind turbines, steam turbines, gas turbines, internal combustion engines, etc.
The working of DC generators is based on Faraday’s law of electromagnetic induction detailed above.
Based upon the output; generators can be classified into two different types:
- AC (Alternating Current) generators.
- DC (Direct current) generators.
TYPES OF DC GENERATORS
There are two major types of DC Generators. This classification is based on the method of field excitation and is as shown below:
- Separately Excited DC generators: As the name implies in this type of generator, filed magnet winding is supplied from an external source.
- Self-Excited DC Generators: These generators have field magnet winding being supplied from the output of the generator itself. Furthermore, these types of generators can be classified into three different types:
- Series Wound Generators: In this type, the field winding is connected in series with armature winding due to the whole current flowing through the field winding and the load.
- Shunt Wound generators: In this type, the field winding is connected in parallel with the armature winding, due to which only a part of armature current flows through shunt field winding, and the remaining current flows through the load.
- Compound wound Generators: It is a combination of the above two. There are two sets of field windings on each pole, one is parallel to the armature, and one is in series with the armature.
Parts of DC Generator
DC generator consists of various parts, which are detailed in below table:
Part Description Armature core or rotor It is one of the essential parts of the DC generator, cylindrical in structure and laminated to avoid loss of currents due to eddy current. This cylindrical core includes slotted iron laminations with slots stacked together to give the core a cylindrical shape. Stator It is also one of the essential parts and consists of two sets of magnets whose purpose is to provide a stable magnetic field in the region where the coil spins. Both the magnets are placed with reverse poles facing each other. Yoke It is the external cylindrical structure of the DC generator. It provides the mechanical power for carrying the magnetic flux given through the poles. Commutator The primary purpose of a commutator is to convert alternating current into direct current. It is made up of copper segments, and each segment is protected from the other with the help of mica sheets. Poles Their primary purpose is to support the field windings which are wound on them. These filed windings can be connected in series or parallel and help increase the cross-sectional area of the magnetic circuit. Pole Shoe They help spread the magnetic flux and simultaneously protect the field coil from falling. Armature Winding These are present in the armature core and can be in series or parallel to increase the cross-sectional area of the magnetic circuit. Brushes They are made up of carbon blocks and ensure the electrical connection between the external load circuit and the commutator. Shaft It is made up of mild steel with maximum breaking strength, and all the rotating parts such as armature core, cooling fans, etc., are attached to it.
Applications of DC generator
There are various uses of DC generator, which are as mentioned below:
- Since DC type generators can produce a wide range of voltage output, they are used in laboratories and commercial testing.
- They are used for supplying power to DC motors.
- They are used in series arc lighting also for voltage boosting applications in the feeders.
- They can be used for battery charging applications as well as for lighting and power supply purposes.
Losses in DC generators
There is a loss of energy in DC generators, too, i.e. complete mechanical energy form is not converted 100% into electrical energy. These losses are majorly of three types:
- Copper Loss: This kind of loss occurs in the armature and field copper windings, which further consist of armature copper loss, field copper loss and brush contact resistance loss.
- Iron Loss: This type of loss consists of eddy current loss and hysteresis loss and occur in the armature iron core, thus classified in iron loss.
- Mechanical Loss: This loss is due to friction in bearings and commutator and contributes 10-20% of total loss.
Conclusion
Operating in accordance with Faraday’s laws of induction, DC generators serve great purposes in practical usage. Now that you know about DC generators, why not learn a bit more about AC Generators too?
