- Electrical Machines - Discussion
- Electrical Machines - Resources
- Electrical Machines - Quick Guide
- 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
- Electrical Machines - Home
Selected Reading
- Who is Who
- Computer Glossary
- HR Interview Questions
- Effective Resume Writing
- Questions and Answers
- UPSC IAS Exams Notes
Types of DC Motors
In practical DC motors, the magnetic field is produced by electromagnets rather than permanent magnets. DC motors are then classified based on the connection of field winding in the motor circuit. On this basis, DC motors are classified into the following two types −
Separately Excited DC Motors
Self-Excited DC Motors
Separately Excited DC Motor
A DC motor whose magnetic field winding is excited from an independent source of DC electric supply pke a battery is called a separately excited DC motor. Figure-1 shows the connection diagram of a separately excited DC motor.
![S DC](/electrical_machines/images/s_dc.jpg)
The speed of a separately excited DC motor depends upon the supply voltage and field current, i.e. magnetic flux in the machine. However, the separately excited DC motors are rarely used in practical apppcations because these require an external source of DC power for field excitation.
Self-Excited DC Motors
The type of DC motor whose magnetic field winding is excited from the same power supply from which the armature is suppped, is known as a self-excited DC motor.
Depending upon the manner in which the field winding is connected with the armature winding, self-excited DC motors are classified in the following three types −
Series DC motor
Shunt DC motor
Compound DC motor
Series DC Motor
A DC motor whose field winding is connected in series with the armature winding so that whole armature current passes through the field winding is called a series DC motor. Figure-2 shows the connection diagram of a series DC motor.
![DC Series](/electrical_machines/images/dc_series.jpg)
In case of a series DC motor, the field winding carries the whole armature current, thus it is made up of thick wire with less number of turns so that it possesses minimum resistance.
The following are some important expressions for the series DC motor −
$$mathrm{mathrm{Armature:current},mathit{I_{a}}:=:mathit{I_{se}}:=:mathit{I_{s}}}$$
Where, $mathit{I_{se}}$ is the series field current and $mathit{I_{s}}$ is the supply current.
$$mathrm{mathrm{Supply:voltage},mathit{V_{s}}:=:mathit{E_{b}+I_{a}left ( mathit{R_{a}+R_{se}} ight )}}$$
Where, $mathit{E_{b}}$ is the back EMF, $mathit{R_{a}}$ is the armature circuit resistance, $mathit{R_{se}}$ is the series field resistance.
Shunt DC Motor
A DC motor whose field winding is connected in parallel with the armature winding so that total supply voltage is appped across it, is known as a shunt DC motor. Figure-3 shows the connection diagram of a shunt DC motor.
![DC Shunt](/electrical_machines/images/dc_shunt.jpg)
In a shunt DC motor, the shunt field winding has a large number of turns of thin wire so that it has high resistance, and therefore only a part of supply current flows through it and the rest flows through the armature winding.
Following are the important expressions of a shunt DC motor −
$$mathrm{mathrm{Armature:current,}mathit{I_{a}}:=:mathit{I_{s}-I_{sh}}}$$
$$mathrm{mathrm{Shunt:field:current,}mathit{I_{sh}}:=:mathit{frac{V_{s}}{R_{sh}}}}$$
$$mathrm{mathrm{Supply:Voltage,}mathit{V_{s}}:=:mathit{E_{b}+I_{a}R_{a}}}$$
Compound DC Motor
A compound DC motor is one which has two sets of field windings on each magnetic pole – one is in series and the other is in parallel with the armature winding.
Compound DC motors are sub-spanided into the following two types −
Short-shunt compound DC motor
Long-shunt compound DC motor
A short-shunt compound DC motor is one in which only shunt field winding is in parallel with the armature winding as shown in Figure-4.
![short ShuntDC](/electrical_machines/images/short_shuntdc.jpg)
A long-shunt compound DC motor is one in which shunt field winding is in parallel with both series field winding and armature winding as shown in Figure-5.
![Long ShuntDC](/electrical_machines/images/long_shuntdc.jpg)
The following are the important expressions for compound DC motors −
For short-shunt motor,
$$mathrm{mathrm{Armature:current,}mathit{I_{a}}:=:mathit{I_{s}-I_{sh}}}$$
$$mathrm{mathrm{Series:field:current,}mathit{I_{se}}:=:mathit{I_{a}}}$$
$$mathrm{mathrm{Shunt:field:current,}mathit{I_{sh}}:=:frac{mathit{V_{s}}-mathit{I_{se}R_{se}}}{R_{sh}}}$$
$$mathrm{mathrm{Supply:voltage},mathit{V_{s}}:=:mathit{E_{b}+I_{a}R_{a}+I_{se}R_{se}}}$$
For long-shunt motor,
$$mathrm{mathrm{Armature:current,}mathit{I_{a}}:=:mathit{I_{s}-I_{sh}}}$$
$$mathrm{mathrm{Series:field:current,}mathit{I_{se}}:=:mathit{I_{s}}}$$
$$mathrm{mathrm{Shunt:field:current,}mathit{I_{sh}}:=:frac{mathit{V_{s}}}{R_{sh}}}$$
$$mathrm{mathrm{Supply:voltage},mathit{V_{s}}:=:mathit{E_{b}+I_{a}left ( R_{a}+R_{se} ight )}}$$
Advertisements