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.
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.
Read More: AC 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.
Read More: Eddy Current
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.
The emf equation of the DC generator is given by the equation:
\(\begin{array}{l}E_g=\frac{P\phi ZN}{60 A}\end{array} \)
where
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.
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:
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.
A few applications of DC generators are:
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
Q1
A DC generator is an electrical machine whose main function is to convert mechanical energy into electricity.
Q2
Types of generators are:
Q3
True.
Q4
The external structure of the DC generator is known as Yoke.
Q5
Types of self excited generator are:
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Machines that convert mechanical energy into electrical energy are called Electric Generators. The electrical energy generated is further transmitted and distributed through power lines for domestic, commercial use. There are two types of generators,
AC Generator
DC Generator
A DC generator is the type of electrical generator that converts mechanical energy into direct current electricity. However, a generator that converts mechanical energy into alternating current electricity is an AC generator.
Do you know why we study generators in their working principle? On this page, we will get to resolve all our queries on the DC generator's parts,working principle and how we describe it in mathematical terms.
What About DC Generators?
In DC generators, the energy conversion is based on the principle of dynamically induced EMF production. These generators are most suitable for off-grid applications. DC generators supply continuous power to electric storage instruments and power grids (DC).
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DC Generator consists of the following parts -
Stator - A stator is a set of two magnets placed in such a way that opposite polarity faces each other. The purpose of the stator is to provide a magnetic field in the region where the coil spins.
Rotor - A rotor is a cylindrical laminated armature core with slots.
Armature Core - The armature core is cylindrical in shape and has grooves on the outer surface. These slots accommodate armature winding in it.
Armature Winding - These are the insulated conductors placed in the armature core. Because of them, the actual conversion of power takes place.
Field Coils - To produce the magnetic field, field coils are placed over the pole core. The field coils of all the poles are connected in series. When current flows through them, adjacent poles acquire opposite polarity.
Yoke - The outer hollow cylindrical structure is known as Yoke. It provides support to main poles and inter poles and gives a low reluctance path for the magnetic flux.
Poles - The main function of the poles is to support the field coils. It increases the cross-sectional area of the magnetic circuit, which results in a uniform spread of magnetic flux.
Pole Shoe - To protect the field coil from falling and to enhance the uniform spread of magnetic flux pole shoe is used. The pole shoe is fixed to Yoke.
Commutator - The commutator is cylindrical in shape. Several wedge-shaped, hard drawn copper segments form a commutator. The functions of a commutator:
To connect stationary external circuits to the rotating armature conductors through brushes and
To convert induced alternating current into direct current.
Working Principle of a DC Generator
A DC generator operates on the principle of Faraday&#;s laws of electromagnetic induction. According to Faraday&#;s law, whenever a conductor is placed in a fluctuating magnetic field (or when a conductor is moved in a magnetic field) an EMF is induced in the conductor.
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If the conductor is guided with a closed path, the current will get induced. The direction of the induced current (given by Fleming&#;s right-hand rule) changes as the direction of movement of the conductor changes.
For example, consider the case, an armature rotating in clockwise direction and conductor at the left moving in an upward direction. As the armature completes its half rotation the direction of movement of the conductor will get reversed downward. The direction of the current will be alternating. As the connections of armature conductors get reversed, a current reversal takes place. Thus, we get unidirectional current at the terminals.
EMF Equation of a DC Generator
The EMF equation for DC generator is expressed as:
Eg = (PØNZ)/60A
Where,
Eg - Generated EMF across any parallel path
P - Total number of poles in the field
N - Rotational speed of armature(rpm)
Z - Total number of armature conductors in the field.
Ø- Magnetic flux produced per pole.
A - number of parallel paths in the armature.
Losses in DC Generators
While converting the mechanical energy into electrical energy, there are losses of energy i.e. whole input isn&#;t converted into output. These losses are classified into mainly three types:
Copper Loss- These losses occur while current flows through windings and are of three types: armature copper loss, field copper winding loss and losses because of brush resistances.
Iron Losses- Due to the induction of current in the armature, eddy current losses and hysteresis loss occur. These losses are also called Core losses or Magnetic losses.
Mechanical Losses- Losses which occur because of friction between the parts of the generator are called mechanical losses.
Types of DC Generators
The three types of self-excited DC generators are:
Series Wound Generators.
Shunt Wound Generators.
Compound Wound Generators.
Applications of DC Generators
Applications of DC generators are as follows:
The separately excited type DC generator is used for power and lighting purposes using the field regulators.
The series DC generator is used in arc lamps for stable current generator, lighting and booster.
Level compound DC generators are used to supply power to hostels, offices, lodges.
Compound DC generators are used for supplying power to DC welding machines.
A DC generator is used to compensate for the voltage drop in the feeders.
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