- Electrical Machines Tutorial
- Electrical Machines - Home
- Basic Concepts
- Electromechanical Energy Conversion
- Energy Stored in a Magnetic Field
- Singly-Excited and Doubly Excited Systems
- Rotating Electrical Machines
- Faraday’s Laws of Electromagnetic Induction
- Concept of Induced EMF
- Fleming’s Left Hand and Right Hand Rules
- Transformers
- Electrical Transformer
- Construction of Transformer
- EMF Equation of Transformer
- Turns Ratio and Voltage Transformation Ratio
- Ideal and Practical Transformers
- Transformer on DC
- Losses in a Transformer
- Efficiency of Transformer
- Three-Phase Transformer
- Types of Transformers
- DC Machines
- Construction of DC Machines
- Types of DC Machines
- Working Principle of DC Generator
- EMF Equation of DC Generator
- Types of DC Generators
- Working Principle of DC Motor
- Back EMF in DC Motor
- Types of DC Motors
- Losses in DC Machines
- Applications of DC Machines
- Induction Motors
- Introduction to Induction Motor
- Single-Phase Induction Motor
- Three-Phase Induction Motor
- Construction of Three-Phase Induction Motor
- Three-Phase Induction Motor on Load
- Characteristics of 3-Phase Induction Motor
- Speed Regulation and Speed Control
- Methods of Starting 3-Phase Induction Motors
- Synchronous Machines
- Introduction to 3-Phase Synchronous Machines
- Construction of Synchronous Machine
- Working of 3-Phase Alternator
- Armature Reaction in Synchronous Machines
- Output Power of 3-Phase Alternator
- Losses and Efficiency of 3-Phase Alternator
- Working of 3-Phase Synchronous Motor
- Equivalent Circuit and Power Factor of Synchronous Motor
- Power Developed by Synchronous Motor
- Electrical Machines Resources
- Electrical Machines - Quick Guide
- Electrical Machines - Resources
- Electrical Machines - Discussion
Construction of DC Machines
An electromechanical device which can convert direct current (dc) electricity into mechanical energy or mechanical energy into direct current (dc) electricity is known as a DC machine.
If the DC machine converts DC electrical energy into mechanical energy, it is known as DC motor. If the machine converts mechanical energy into DC electrical energy, then it is known as a DC generator. Both DC motor and DC generator have the similar construction.
A typical DC machine consists of the following major parts −
Yoke or Frame
Armature
Field System
Commutator
Brushes
Bearings
The schematic diagram of a DC machine is shown below −
Let us now discuss each of these components in greater detail.
Yoke or Frame
The yoke is the outer frame of the DC machine. It is made up of such materials that have high permeability and high mechanical strength. In practice, the yoke of DC machine is made up of cast steel.
The yoke or frame of the DC machine serves the following main purposes −
It protects the internal machine parts like armature, windings, field poles, etc. against mechanical damages.
The yoke houses the magnetic field system.
It provides a low reluctance path to the working magnetic flux.
It supports the rotor or armature through bearings.
Armature
In DC machines (motor or generator), armature is a system of conductors or coils that can rotate freely on the supporting bearings. The working torque and EMF are developed in coils of the armature. The armature consists of two main parts namely, armature core and armature winding.
The armature core is a solid cylindrical structure, made up of high permeability thin silicon steel laminations. On the outer periphery of the core slots are cut to carry the armature winding.
The armature winding is made up of copper wires. The armature winding of DC machine is generally former wound. Depending upon the end connections of the armature conductors, the armature winding may be of two types namely lap winding and wave winding. The type of winding decides the voltage and current rating of the machine. In case of the lap winding, the number of parallel paths (A) for current to flow are equal to the number of poles (P) in the machine. On the other hand, for wave winding, the number of parallel paths (A) are equal to 2.
Field System
Field system is the part of a DC machine which produces the working magnetic flux in the machine. It is basically a system of electromagnets which is excited by a DC supply. In case of DC machine, the field system is a stationary part of the machine and it is bolted to the yoke or frame of the machine. There are three main parts of a field system in dc machines namely pole core, pole shoes, and field coils.
The pole core is made up of thin steel laminations. One end of the pole core is bolted to the frame and other end has pole shoe. The pole core carries the field winding.
The pole shoe is a projected part of the pole core and has a large area of cross-section. Pole shoes help in spreading the magnetic flux uniformly in the air gap, and offers low reluctance path to the magnetic flux. Also, it supports the field winding.
The field coil or winding is made up of copper wire. The field winding is former wound and inserted around the pole core. When field windings are excited by DC supply, they become electromagnets and produce magnetic flux in the machine.
Commutator
The commutator is one of the important parts of the DC machine. It is basically mechanical rectifier. It is a cylindrical shaped device and is made up of copper. The outer periphery of the commutator has V-shaped slots to carry commutator segments. Where, the commutator segments are copper bars inserted in the slots. These segments are insulated from each other by mica. The commutator is mounted on the shaft of the DC machine on one side of the armature. The armature conductors are connected to the commutator segments with the help of copper lugs.
The commutator performs the following two major functions −
In a DC generator, it collects the current from the armature conductor. In a DC motor, it supplies the current to the armature conductors.
It converts the alternating current of the armature into unidirectional current in the external circuit with the help of brushes, and vice-versa.
Brushes
Brushes are used to make an electrical connection with the rotating commutator. These collect (or supply) current from (or to) the moving commutator. Brushes are usually made up of carbon. They are housed in brush holders and are in contact with the commutator surface with the help of spring pressure.
Bearings
Bearings are used in the DC machine to reduce the frictional losses. Thus, the main function of bearings in the DC machine is to support the machine shaft with minimum friction. In DC machines, ball bearings or roller bearings are commonly used.
To Continue Learning Please Login