Electrical generators are standalone machines that provide electricity when power from the local grid is unavailable. These generators supply backup power to businesses and homes during power outages. Generators do not create electrical energy, but they convert mechanical or chemical energy into electrical energy. Based on the output, generators are classified into two types as AC generators and DC generators. In this article, we will be discussing DC generators in detail. You can check out our article on the AC generator to understand its working principle, construction and more.
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What is a DC Generator?
A DC generator is an electrical machine whose main function is to convert mechanical energy into electricity. When the conductor slashes magnetic flux, an emf will be generated based on the electromagnetic induction principle of Faraday’s Laws. This electromotive force can cause a flow of current when the conductor circuit is closed.
Parts of a DC Generator
A DC generator can also be used as a DC motor without changing its construction. Therefore, a DC motor, otherwise a DC generator, can be generally called a DC machine. Below we have mentioned the essential parts of a DC Generator.
The main function of the stator is to provide magnetic fields where the coil spins. A stator includes two magnets with opposite polarities facing each other. These magnets are located to fit in the region of the rotor.
A rotor in a DC machine includes slotted iron laminations with slots that are stacked to shape a cylindrical armature core. The function of the lamination is to decrease the loss caused due to eddy current.
Armature windings are in a closed circuit form and are connected in series to parallel to enhance the produced current sum.
The external structure of the DC generator is known as Yoke. It is made of either cast iron or steel. It provides the necessary mechanical power for carrying the magnetic flux given through the poles.
The function of a pole is to hold the field windings. These windings are wound on poles and are either connected in series or parallel by the armature windings.
Pole shoe is mainly utilized for spreading the magnetic flux to prevent the field coil from falling.
A commutator works like a rectifier that changes AC voltage to DC voltage within the armature winding. It is designed with a copper segment, and each copper segment is protected from the other with the help of mica sheets. It is located on the shaft of the machine.
The electrical connections can be ensured between the commutator as well as the exterior load circuit with the help of brushes.
How does a DC Generator Work?
According to Faraday’s law of electromagnetic induction, we know that when a current-carrying conductor is placed in a varying magnetic field, an emf is induced in the conductor. According to Fleming’s right-hand rule, the direction of the induced current changes whenever the direction of motion of the conductor changes. Let us consider an armature rotating clockwise and a conductor at the left moving upwards. When the armature completes a half rotation, the direction of the motion of the conductor will be reversed downward. Hence, the direction of the current in every armature will be alternating. But with a split ring commutator, connections of the armature conductors get reversed when a current reversal occurs. Therefore, we get a unidirectional current at the terminals.
Read more about Fleming’s right-hand rule here.
E.M.F Equation of DC generator
The emf equation of the DC generator is given by the equation:
Z is the total number of armature conductor
P is the number of poles in a generator
A is the number of parallel lanes within the armature
N is the rotation of armature in r.p.m
E is the induced e.m.f in any parallel lane within the armature
Eg is the generated e.m.f in any one of the parallel lane
N/60 is the number of turns per second
The time for one turn will be dt=60/N sec.
Losses in DC Generator
The input power is not fully transformed into the output power in a DC machine. Some part of input power gets wasted in various forms. In a DC machine, the losses are broadly classified into four types:
- Copper Loss
Copper loss takes place when the current flows through the winding. These losses occur due to the resistance in the winding. The copper loss is categorized into three forms armature loss, the field winding loss and brush contact resistance loss.
- Core Losses or Iron Losses
Some losses in the iron core occur when the armature rotates in the magnetic field. These losses are known as core losses. These losses are categorized into two losses as Hysteresis loss and Eddy current loss.
Types of DC generator
The DC generator can be classified into two main categories as separately excited and self-excited.
The field coils are energized from an independent exterior DC source in a separately excited type generator.
In a self-excited type, the field coils are energized from the generated current within the generator. These types of generators can further be classified into a series of wounds, shunt-wound, and compound wound.
Applications of DC Generators
A few applications of DC generators are:
- The separately excited type DC generators are used for power and lighting purposes.
- The series DC generator is used in arc lamps for lighting, stable current generator and booster.
- DC generators are used to reimburse the voltage drop within Feeders.
- DC generators are used to provide a power supply for hostels, lodges, offices, etc.
This was a comprehensive explanation about DC generators. From the information above, we can conclude that the main advantages of a DC generator are its simple construction and design.
Frequently Asked Questions – FAQs
What is a DC generator?
What are the types of generators?
Types of generators are:
State true or false: Without changing the construction, DC generator can be used as a DC motor.
What are the types of self excited generator?
Watch the video and explore the differences between AC and DC.
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