Electrical Machines

At the end of the course the student should be able to: 1. explain operating principles of fundamental components of Electric Machines: motors, generators and transformers including synchronous, asynchronous, DC and special purpose motors, AC, DC generators and autotransformers, CTs, PTs, step-up and step- down transformers; 2. examine the magnetic field, reluctance of magnetic materials, flux and mmf in magnetic circuits and perform transformer analysis using standard testing procedures including open-circuit and short-circuit tests, voltage regulation, efficiency and circuit analysis involving transformers; 3. examine construction, working principles, characteristics and equivalent circuit of three phase synchronous generators, synchronous motors and induction motors, single phase induction and special purpose motors; and 4. analyse voltage-current characteristics, commutation of DC generators, torque speed characteristics and speed regulation of DC motors.

DC Machine, Introduction to Machinery Principles, Rotational motion, Newton’s Law and power relationships, the Magnetic field, Magnetic Circuit with air gap, Faraday’s law, Production of induced force on wire, Induced voltage on a conductor moving in a magnetic field, Linear DC machine.; DC Machinery Fundamentals: Simple rotating loop between curved pole faces, Commutation, Construction, Simple armature winding, Armature reaction, Interpoles, compensating winding and brush shifting, Internal generated voltage and induced torque equations of real machines; DC Generators, Introduction, Voltage regulation, Magnetization curve, Equivalent circuits, Working and characteristics of separately excited, shunt, series and compounded generators, Parallel operations of direct current generators; DC Motors, Introduction, Speed regulation, Equivalent Circuits, Working and Characteristics of separately excited, Shunt and Permanent magnet, Working and Characteristics of series and compounded motors, Torque–speed Equations, Efficiency calculations, Stepper Motor and Drive circuit.; AC Machines Topics, Transformer Fundamentals, Importance of transformers, Types and construction, The ideal transformer, Leakage reactance, Theory and operation of single phase transformer, Losses and phasor diagram, the equivalent circuit of a real transformer, No load and short circuit test, the per unit system, the transformer voltage regulation and efficiency, Autotransformers and concept of its power rating advantages, Current transformer (CT) and Potential transformer (PT), Three phase Transformers, Construction of power Transformer, Three phase connections and harmonics suppression, Vector groups, Three phase transformer using two transformers, Transformer ratings and related problems, Transformer Inrush Current, AC Machines Fundamentals, A simple loop in a uniform magnetic field, Review of three phase generation, Proof of the rotating magnetic field concept and its relation with no. of poles, the relationship between electrical and mechanical degree, the relationship between electrical frequency and the speed of the magnetic field rotation Induced voltage and induced torque, Losses and power flow diagram, Voltage regulation and speed regulation.; Synchronous Generator, Construction, Excitation system, Equivalent circuit of Synchronous Generator, Phasor diagram, Power and Torque, Measurement of model parametres, Effect of load changes on a generator, Parallel operation of generators; Synchronous Motor, Basic principle of motor operation, Equivalent circuit, Torque speed characteristics, Power and torque equation, Phasor diagram, the effects of load change, and field current change, V- curves of synchronous motor and power factor correction, Starting of synchronous motor, Synchronous motor ratings; Three Phase Induction Motor, Construction, Basic concepts and working principles, Synchronous speed, Slip and its effect on rotor frequency and rotor voltage, Equivalent circuit, Power and torque, Torque speed characteristics, losses, efficiency and power factor; Single Phase and Special Purpose Motors, The Universal motor, Introduction to single phase induction motor, Starting single phase induction motors, Split phase windings, Capacitor start motor, Permanent split capacitor motor, Capacitor start and capacitor run motors, Shaded pole motors, Reluctance motors, the Hysteresis motor.