 # Electrical Machines - I

#### Features Includes:

• 150 - 3D/2D Animation
• 850 Pages of Content
• 60 Lecture Hours
• 80 Solved Problems
• 100 Quiz
• Suitable for All Technical University Syllabus

#### Course Description

This learning solution covers a whole range of machines that include D.C. Motors, D.C. Generators. It provides a comprehensive coverage of working principle, Types, Characteristics, testing and applications of DC machines.

#### OBJECTIVES:

• To introduce techniques of magnetic circuit analysis and introduce magnetic materials.
• To study the working principles of electrical machines using the concept of electromechanical energy conversion principles and derive expression for generated voltage and torque developed in all Electrical machines.
• To study the working principles of DC machines as Generator types, determination of thier no/load characteristics, starting and methods of speed control of motors.
• To Understand the working principle of DC motor, types,characteristics and applications.
• To estimate the various losses taking place in D.C. motor and to study the different testing methods to arrive at their performance.
###### UNIT I - MAGNETIC CIRCUITS

Introduction to engineering Mechanics - Introduction, Types of electrical machines. Magnetic circuits - Magnetic circuits, Series magnetic circuits, Parallel magnetic circuits, Problems based on magnetic circuits. Definitions of magnetism - Magnetic Flux, Definitions concerning magnetic circuit. Faraday's laws of electromagnetic induction - Introduction, Faraday's law of electromagnetic induction, Problem based on Faraday’s law. Lenz's law and Fleming's law - Direction of induced e.m.f. and current. Principle of self and mutual induction - Induced e.m.f, Dynamically induced E.M.F, Self inductance, Mutual inductance, Coefficient of coupling, Problem based on coefficient of coupling. Energy stored in a magnetic field - Energy stored in a magnetic field. Force on a conductor placed on a magnetic field - Force between two parallel current carrying conductors, The mechanical force on a current carrying conductor inside a magnetic field (Forward current), Magnetic field around a current carrying conductor. B-H relationship - B-H Curve or magnetization curve, B-H Curve and permeability, Steps in obtaining hysteresis loop, Theory behind hysteresis effect, Hysteresis loss per unit volume, Practical use of hysteresis loop. A.C. operation of magnetic circuits - A.C. Operation of magnetic circuits, Energy Stored under A.C. Operation. Introduction to permanent magnets - Permanent magnets, Transformer as coupled circuit.

###### UNIT II - ELECTROMECHANICAL ENERGY CONVERSION

Introduction - Law of Electromagnetism, Energy flow in Electromechanical energy conversion device. Magnetic system - Types of magnetic system, Singly excited magnetic system, Concept of co-energy, Mechanical force, Direction of mechanical force, Mechanical energy. Problems based on single excited magnetic system - Problems based on magnetic system, Comparision between lap winding and wind winding. Multiple excited magnetic system - Multiple excited magnetic system, Problem based on multiple excited magnetic system. Energy conversion via electric field - Analysis of energy conversion, Co-energy calculations. Elementary concept of rotating machines - Introduction, General construction of rotating machines, Basic d.c. machine, Basic synchronous machines, Working principle of synchronous machine, Generated voltage in d.c. machines, Three phase winding in a.c. machines, Types of three phase windings, Generated voltage in A.C. machines, Pitch factor or coil span factor (Kc), Generalized expression for E.M.F. equation of an alternator. MMF of distributed winding - M.M.F. of distributed a.c. windings, M.M.F. space wave of one phase of distributed winding, Flux and mmf. phasors in synchronous machines. Rotating magnetic field - Rotating Magnetic Field, Speed of Rotating Magnetic Field, Production of rotating field, Graphical representation, Mathematical Proof. Working principle of basic induction machine - Working principle of basic induction machine, Alternatively this can be explained, Torque in Round Rotor Machine, Derivation of Torque Equation for Round Rotor Machine. Selection of motor for industrial applications - Selection of motor for industrial applications, Cranes and Hoists, Coal and Mining Industry.

###### UNIT III - D.C.GENERATORS

D.C. Generator construction - Construction of D.C. generator, Magnetic frame or yoke, Pole cores and pole shoes, Pole coils, Armature, Commutator, Brushes, Bearings, End covers or end housings, Shaft and Pulley. Working principle of D.C. Generator - Working operation of simple loop generator, Working principle of D.C. generator. Lap and wave winding - Armature windings, Terms used in armature winding, Coil or winding element, Terms used in armature winding, Type of D.C. armature windings. EMF Equation -E.M.F. equation of D.C. generator, Problems & Exercises based on E.M.F equation of d.c. generator, Flux distribution. Types of generators - What do you mean by excitation?, Classification of D.C. generators, Types of D.C. generator, Series generator, Problems & Exercises based on d.c. series generator. Types of generators - D.C. shunt generator, Problems & Exercises based on d.c. shunt generator, Compound generator, Problems & Exercises based on long shunt compound generator. Armature reaction - Armature reaction, Demagnetising and cross-magnetising conductors, Demagnetising AT per pole, Cross-Magnetising AT per pole, Compensating windings. Problems - Problem based on demagnetising and cross magnetising of pole. Commutation – Commutation, Methods of improving commutation, E.M.F. commutation, Equalizing connections. Power flow diagrams - Power stages in D.C. generator, Types of generator efficiencies. Condition for building up and non-building up of EMF - Residual magnetism, Conditions for non-building up of E.M.F. in D.C. generator, Causes of failure to excite self excited generator. Calculation of critical field resistance and critical speed - Critical field resistance and critical speed, Critical resistance for shunt generator, Calculation of critical speed, Problem based on critical field resistance and critical speed. Characteristics of D.C. generators - Load Characteristics D.C. Generators, Load characteristics of D.C. Shunt Generator, Load characteristics of D.C. Series Generator, Load Characteristics D.C. Compound Generators. Applications of D.C. generators - Applications of D.C. generators. Necessity of parallel operation - Conditions necessary for parallel operation. Conditions for parallel operation of D.C. generators - Paralleling D.C. generator, Load sharing, Procedure for paralleling D.C. generator, Problem based on parallel operation of D.C. generators. Use of equalizer ring in parallel operation and applications of D.C. generators - Compound generator in parallel, problem based on compound generator in parallel, Series generator in parallel, Problem based on series generator in parallel.

###### UNIT IV - D.C. MOTORS

Working principle of D.C. Motor - Working of D.C. motor. Back e.m.f - Signification of the back E.M.F, Importance of back E.M.F. Torque and speed equation - Torque equation, Speed-torque equation, Problems based on motor torque and speed. Types of D.C. motor - Classification of D.C. motor, D.C. series motor, Problem based on d.c. series motor, D.C. shunt motor, Problem based on d.c. shunt motor, D.C. compound motor. Characteristics - D.C. Motor characteristics, Characteristics of D.C. shunt motor, Characteristics of D.C. series motor, Characteristics of D.C. compound motor, Application of D.C. motor. Effect of armature reaction on performance of a D.C. motor - Effect of armature reaction on performance of a D.C. motor. Speed control - Necessity of speed control, Methods of speed control, Armature control (or) Rheostatic control method, Voltage control method, Problem based on speed control of dc shunt motor. Speed control of series motor - Problem based on speed control of dc series motor. Starter - Necessity of starter, Three point starter, Function of no volt coil, Action of over load release, Speed control, Four point starter, Necessity of the starter for d.c. series motor, Drum controlled starter. Braking and it's applications - Electric braking, Plugging, Rheostatic braking (Dynamic braking), Regenerative braking, Comparison of Plugging, Regenerative and Rheostatic braking methods, Characteristics of D.C.compound motors, Differential D.C.compound motors. Permanent magnet dc motor - Permanent magnet D.C. motor.

###### UNIT V - TESTING OF D.C. MOTORS

Introduction - Losses in a D.C. machine. Efficiency of D.C. machine - Types of generator efficiencies, Problems based on efficiency. Testing of motors - Testing of d.c. motors, Brake test on d.c. shunt motor, Brake test on d.c. series motor, Brake test on d.c. cumulative compound motor, Swinburne’s test, Advantage and disadvantage, Regenerative or Hopkinson’s test (back-to-back test), Methods of procedure, Alternative connections for Hopkinson’s test, Merits of Hopkinson’s test, Problem based on testing of dc motor, Retardation or Running down test, Field’s Test For Series Motor. Separation of No load losses of D.C. Machines - Separation of No load losses of D.C. Machines, Problem based on separation of no load losses.