DC Machines Chapter 1: Theory Of Operation & Construction  Chapter 2: DC Machines On Load  Chapter 3: DC Generators  Chapter 4: DC Motors  1 References S.J. Chapman, "Electric Machinery Fundamentals", McGraw Hill, 4th edition, 2005. 2 Chapter 1 Theory Of Operation & Construction 1. Introduction 2. Electromechanical Energy Conversion 3. DC Machines Theory of Operation 4. Construction 5. Classification of DC Machines 6. Armature Voltage and Developed Torque 3 Electric Machine Mechanical Electrical Electrical Mechanical Motor Generator Input Output Input Output Electromechanical Energy Conversion i + w T Mechanical system v Electrical system Ideal Electric Machine _ Motor Energy Flow v i=T w Generator 4 Principle of Operation If a conductor of length l moves at a linear speed v in a magnetic field the induced voltage in the conductor is Faraday’s law or e=Blv e e flux cutting rule N v v B S B Right hand rule 5 Principle of Operation For the current carrying conductor of length l the force known as Lorentz force produced is i i N F F F=Bli B S B Left hand rule 6 Induced e.m.f e e  N v v B e = B l v S B Right hand rule Electromagnetic Force  i i N F F B F = B l i S B Lift hand rule 7 DC Machines theory of operation N N e N e e w w w S S S and for multiturn machine 8 Generated Voltage (EMF) For counter-clockwise motion the rotor terminal under  the N pole is always positive with respect to that under the S pole. The brush terminal B1 is always positive and B2 is  negative so e12 is unidirectional 9 DC Machines DC currents are required for both its field winding ( stator ) and armature winding (Rotor) DC machine mainly used as DC motors DC motors is characterized by superior torque and a wide range of speed DC machine is more costly than comparable AC machine and their maintenance cost is higher. 10