JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD

Prerequisite

Electrical Machines-I

Course Objectives:

• To deal with the detailed analysis of polyphase induction motors & Synchronous generators and motors
• To understand operation, construction and types of single phase motors and their applications in house hold appliances and control systems.
• To introduce the concept of parallel operation of synchronous generators.
• To introduce the concept of regulation and its calculations.

Course Outcomes

After this course, the student

• Identify different parts of transformers and induction motors and specify their functions
• Understand the operation of transformers and induction motors
• Carry out different testing methods and assess the performance of transformers and induction motors
• Start and control the induction motor

UNIT - I

Polyphase Induction Motors: Constructional details of cage and wound rotor machines- production of a rotating magnetic field - principle of operation - rotor EMF and rotor frequency - rotor reactance, rotor current and Power factor at standstill and during operation.

UNIT - II

Characteristics of Induction Motors: Rotor power input, rotor copper loss and mechanical power developed and their inter relation-torque equation-deduction from torque equation - expressions for maximum torque and starting torque - torque slip characteristic - equivalent circuit - phasor diagram - crawling and cogging -.No-load Test and Blocked rotor test – Predetermination of performance-Methods of starting and starting current and Torque calculations. Speed Control Methods: Change of voltage, change of frequency, voltage/frequency, injection of an EMF into rotor circuit (qualitative treatment only)-induction generator- principle of operation.

UNIT - II

Construction, Principle of operation, Characteristics & Regulation of Synchronous Generator: Constructional Features of round rotor and salient pole machines – Armature

windings – Integral slot and fractional slot windings; Distributed and concentrated windings – distribution, pitch and winding factors – E.M.F Equation. Harmonics in generated e.m.f. – suppression of harmonics – armature reaction - leakage reactance – synchronous reactance and impedance – experimental determination - phasor diagram – load characteristics. Regulation by synchronous impedance method, M.M.F. method, Z.P.F. method and A.S.A. methods – salient pole alternators – two reaction analysis – experimental determination of Xd and Xq (Slip test) Phasor diagrams – Regulation of salient pole alternators.

UNIT - IV

Parallel Operation of Synchronous Generator: Synchronizing alternators with infinite bus bars – synchronizing power torque – parallel operation and load sharing - Effect of change of excitation and mechanical power input. Analysis of short circuit current wave form – determination of sub-transient, transient and steady state reactances. Synchronous Motors – Principle of Operation: Theory of operation – phasor diagram – Variation of current and power factor with excitation – synchronous condenser – Mathematical analysis for power developed .- hunting and its suppression – Methods of starting – synchronous induction motor.

UNIT - V

Single Phase Motors & Special Motors:: Single phase induction motor – Constructional features-Double revolving field theory – split-phase motors – shaded pole motor.

TEXT BOOKS:

• 1. “I. J. Nagrath & D. P. Kothari”, “Electric Machines”, Tata Mc Graw Hill, 7 th Edition, 2009
• 2. “PS Bhimbra”, “Electrical machines”, Khanna Publishers, 2014

REFERENCE BOOKS:

• 1. “M. G. Say”, “Performance and Design of AC Machines”, CBS Publishers, 3 rd Edition, 2002.
• 2. “A.E. Fitzgerald, C. Kingsley and S. Umans”, “Electric machinery”, Mc Graw Hill Companies, 7th edition, 2013
• 3. “Langsdorf”, “Theory of Alternating Current Machinery”, Tata McGraw-Hill Companies, 2 nd edition, 1984.
• 4. “M.V Deshpande”, “Electrical Machines”, Wheeler Publishing, 2011