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- Power Developed by Synchronous Motor
- Equivalent Circuit and Power Factor of Synchronous Motor
- Working of 3-Phase Synchronous Motor
- Losses and Efficiency of 3-Phase Alternator
- Output Power of 3-Phase Alternator
- Armature Reaction in Synchronous Machines
- Working of 3-Phase Alternator
- Construction of Synchronous Machine
- Introduction to 3-Phase Synchronous Machines
- Methods of Starting 3-Phase Induction Motors
- Speed Regulation and Speed Control
- Characteristics of 3-Phase Induction Motor
- Three-Phase Induction Motor on Load
- Construction of Three-Phase Induction Motor
- Three-Phase Induction Motor
- Single-Phase Induction Motor
- Introduction to Induction Motor
- Applications of DC Machines
- Losses in DC Machines
- Types of DC Motors
- Back EMF in DC Motor
- Working Principle of DC Motor
- Types of DC Generators
- EMF Equation of DC Generator
- Working Principle of DC Generator
- Types of DC Machines
- Construction of DC Machines
- Types of Transformers
- Three-Phase Transformer
- Efficiency of Transformer
- Losses in a Transformer
- Transformer on DC
- Ideal and Practical Transformers
- Turns Ratio and Voltage Transformation Ratio
- EMF Equation of Transformer
- Construction of Transformer
- Electrical Transformer
- Fleming’s Left Hand and Right Hand Rules
- Concept of Induced EMF
- Faraday’s Laws of Electromagnetic Induction
- Rotating Electrical Machines
- Singly-Excited and Doubly Excited Systems
- Energy Stored in a Magnetic Field
- Electromechanical Energy Conversion
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Working Principle of DC Generator
The working principle of DC generator is based on the Faraday’s law of electromagnetic induction. According to this law, when the magnetic flux pked to a conductor or coil changes an EMF is induced in the conductor or coil. The magnitude of this induced EMF is given by,
$$mathrm{mathit{e}:=:mathit{N}frac{mathit{dphi }}{mathit{dt}}:cdot cdot cdot (1)}$$
Where, $phi$ is the flux pnkage of the coil and N is the number of turns in the coil.
In case of a DC generator, the magnetic flux ($phi$) remains stationary and the coil rotates. The EMF induced where the coil is rotating and flux is stationary, is known as dynamically induced EMF.
![Working Principle](/electrical_machines/images/working_principle.jpg)
In order to understand the working principle of a DC generator, we consider a single loop DC generator (i.e. N = 1) as shown in above figure. Here, the coil is rotated by some prime mover (a source of mechanical energy), and there is a change in the magnetic flux pnkage to the coil.
Let $phi$ be the average magnetic flux produced by each magnetic pole of the machine, then the average induced EMF in the generator is given by,
$$mathrm{mathit{E_{av}}:=:frac{mathit{dphi }}{mathit{dt}}:=:mathrm{Flux: cut: per:sec:by: the :coil}}$$
$$mathrm{Rightarrow mathit{E_{av}}:=:mathrm{Flux: cut: in :one :rotation: imes :No.:of: rotations: per: sec}}$$
$$mathrm{Rightarrow mathit{E_{av}}:=:mathrm{left ( Flux:per:pole imes No.:of:poles ight )}: imes :mathrm{No.:of :rotations :per: sec}}$$
$$mathrm{ herefore mathit{E_{av}}:=:mathit{phi : imes P: imes :n}:cdot cdot cdot (2)}$$
Where, P is the total number of poles in the generator and n is the speed of the coil in rotation per second. The expression in the Equation-(2) gives the average induced EMF in a single loop DC generator.
The following points explain the working principle of a DC generator −
Position 1 − The induced EMF is zero because, the movement of coil sides is parallel to the magnetic flux.
Position 2 − The coil sides are moving at an angle to the magnetic flux, and hence a small EMF is generated in the loop.
Position 3 − The coil sides are moving at right angle to the magnetic flux, therefore the induced EMF is maximum.
Position 4 − The coil sides are cutting the magnetic flux at an angle, thus a reduced EMF is induced in the coil sides.
Position 5 − No flux pnkage with the coil side and the coil sides are moving parallel to the magnetic flux. Therefore, no EMF is induced in the coil.
Position 6 − The coil sides move under a pole of opposite polarity and hence the polarity of induced EMF is reversed. The maximum EMF will induce in this direction at position 7 and zero when it is at position 1. This cycle repeats with rotation of the coil.
In this way, EMF is induced in a DC generator. Though, this induced EMF is alternating in nature, which is then converted in the unidirectional EMF by using a device called commutator.
The direction of induced EMF in the armature conductor of the DC generator is determined by the Fleming’ right hand rule (FRHR) which we discussed in the module-1 (basic concepts) of this tutorial.
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