What is a Generator?
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.
FAQs on DC Generator
1. What is a DC generator?
A DC generator is an electrical machine designed to convert mechanical energy into direct current (DC) electrical energy. Its operation is based on the principle of dynamically induced electromotive force (EMF). These generators are particularly useful for supplying continuous power in off-grid applications, for DC welding, and for charging storage batteries.
2. What is the working principle of a DC generator?
A DC generator operates on the principle of Faraday's law of electromagnetic induction. This law states that an electromotive force (EMF) is induced in a conductor whenever it cuts through magnetic flux lines. In a DC generator, an armature coil is rotated within a magnetic field, which induces a current. The direction of this induced current is given by Fleming's right-hand rule. While the current induced in the rotating armature is initially alternating (AC), a component called a commutator converts it into direct current (DC) at the output.
3. What are the main parts of a DC generator and their functions?
The essential parts of a DC generator include:
- Yoke: The outer frame that provides mechanical support and a path for the magnetic flux.
- Stator (Field Coils & Poles): The stationary part that generates the constant magnetic field.
- Rotor (Armature Core & Winding): The rotating part containing the conductors where EMF is induced.
- Commutator: A segmented copper ring that reverses the current direction, converting the internal AC into output DC.
- Brushes: Carbon or graphite conductors that collect the current from the commutator and deliver it to the external load.
4. What is the key difference between a DC generator and a DC motor?
The fundamental difference between a DC generator and a DC motor is their function of energy conversion. A DC generator converts mechanical energy into electrical energy (e.g., a turbine spinning the armature to produce current). In contrast, a DC motor performs the opposite function, converting electrical energy into mechanical energy (e.g., using current to create rotational force). While their basic construction is very similar, their input and output are reversed.
5. Why is a commutator essential for the operation of a DC generator?
A commutator is essential because the current naturally induced in the rotating armature coil is alternating (AC), as it changes direction with every half rotation. The commutator acts as a mechanical rectifier. Its primary function is to reverse the connection to the external circuit at the same instant the current in the armature coil reverses. This action ensures that the output current always flows in a single direction, effectively converting the internally generated AC into the unidirectional DC required from the generator.
6. What are the different types of self-excited DC generators?
Self-excited DC generators use their own output to energise the field magnets. They are classified based on how the field winding is connected to the armature:
- Series Wound Generator: The field winding is connected in series with the armature.
- Shunt Wound Generator: The field winding is connected in parallel (shunt) with the armature.
- Compound Wound Generator: This type features both series and shunt field windings to combine their characteristics.
7. What causes energy losses in a practical DC generator?
In a practical DC generator, not all input mechanical energy is converted into useful electrical output. The energy losses are categorised as:
- Copper Losses: Heat generated (I²R loss) in the copper windings of the armature and field coils due to electrical resistance.
- Iron Losses (Core Losses): These occur in the armature's iron core and consist of hysteresis loss and eddy current loss due to the changing magnetic field.
- Mechanical Losses: Energy lost due to physical forces, such as friction in the bearings and air resistance (windage) against the rotating armature.
8. Where are DC generators commonly used in real-world applications?
DC generators are employed in various applications where a direct current supply is specifically needed. Common examples include:
- Charging large storage batteries, as they provide a direct current.
- Providing stable current for arc lamps used in cinema projectors and searchlights.
- Acting as boosters to compensate for voltage drops in DC power distribution lines.
- Supplying power for DC welding machines and electroplating processes.
