Upon the introduction of four-year courses for the bachelor of engineering degree based on the (10 + 2) year pattern, AICTE (The All India Council of Technical Education) came up with a model curriculum. Following this curriculum two compulsory courses, namely Electrical Science I and II, have been introduced in most engineering institutions and colleges across the country for students of all engineering disciplines. These courses form the foundation for higher level courses in electrical and electronics engineering degrees, and also serve to introduce electrical sciences to students of other disciplines. Electrical Science-I comprises electric circuit theory and electromechanical energy conversion, while Electrical Science-II covers electronics and instrumentation.

There are some foreign books which cover the above four topics of electrical sciences. However, these are largely beyond the reach of Indian students because of their high cost. Further these books are found unsuitable for the syllabus as defined in the AICTE model because of which these have not appeared in cheap editions. So for quite some time a strong need has been felt for textbooks in this area.

This book is designed to fulfil the need of the Electrical Science-I course. It covers all the essential topics in electric circuit theory and electromechanical energy conversion. It follows the pattern suggested by the Teachers’ Manual for Electrical Science-I, April, 1984, Indian Society of Technical Education, IIT Campus, New Delhi. It is written in a style which lends itself to easy adaptation to the exact syllabi of various universities, and teaching plans of individual teachers. Certain topics can be altogether left out without loss of continuity and others can be partly covered without going into all the details.

Since Electrical Science-I is the only electrical course offered to non-electrical students, it is desirable that the course encompasses the total span of the book. This would in my view requires 5 lectures/week plus preferably a tutorial hour. Where such time is not warranted by the curriculum design of a discipline, a judicious choice of topics must be made.

Electric circuit theory is covered in Chapters 1 to 7 and it encompasses all the basic techniques of circuit analysis. The first chapter introduces circuit elements including sources; elemental relationships and the two basic laws of circuit theory namely Kirchhoff’s Voltage and Current Laws (KVL and KCL). Various types of excitations namely, dc, sinusoidal, step function and other periodic wave shapes are presented in the text as and when the need arises. The techniques of circuit reduction and mesh and nodal analysis are treated through simple resistive circuits (in Chapter 2), and later extended to the more general circuits. A similar approach is used to introduce various network theorems.

In the third chapter, simple techniques of obtaining natural and forced response are illustrated through first and second order circuits. At this stage the forced response is restricted to the case of step functions (dc excitation). The total circuit response is then obtained by combining the two responses with application of initial conditions.

The phasor representation of sinusoidal function is introduced in Chapter 4, before presenting the steady state sinusoidal analysis of circuits. This is followed by a section explaining the transformation from a time domain circuit to a frequency domain circuit. Mesh and nodal analysis and various network theorems are then applied to frequency domain circuits. Concepts of active and reactive power are illustrated here. Response of a circuit to sudden application of sinusoidal excitation is also obtained.

Certain miscellaneous topics—frequency response, Bode diagrams, resonance, Fourier series and analysis, two-port networks—which are a prerequisite for Electrical Science-II are covered in Chapter 5. Chapter 6 discusses the sinusoidal steady state analysis of three-phase balanced circuits and three-phase power. Using these techniques the student can analyse any circuit for determining its transient and/or steady state response.

A full chapter is then devoted to the analysis of circuits using Laplace transformation with various theorems and inversion techniques. The circuit analysis follows the method of transformed networks. The general concept of network function (transfer function) is introduced and the steady state sinusoidal response obtained. This chapter is included for completeness of the text but may be altogether skipped in teaching Electrical Science-I.

Electromechanical energy conversion is covered in Chapters 8 to 13 which treat the basic concepts, transformers and complete range of electric machines including single-phase motors. Steady-state sinusoidal circuit analysis, active and reactive powers and 3-phase circuits discussed in the earlier chapters are used here. The circuit model of each device (static/rotational) is introduced which is then employed in performance calculations.

Beginning with the treatment of magnetic circuits and magnetic materials in Chapter 8, Faraday’s laws are discussed before presenting the generalised article on electromechanical energy conversion. Wherever the teacher is pressed for time he may altogether skip this article. It is independent and is not needed at a later stage.

Chapter 9 covers the circuit model of the transformer, determination of model parameters, voltage regulation and efficiency. Articles on autotransformer and three-phase transformers are also included.

Basic groundwork for rotating machines is laid in the chapter on emf and torque. While the derivation of emf equation is sufficiently detailed, the treatment of mmf is brief and comprises a section on the rotating magnetic field. These ideas are then extended to torque development in a rotating machine with illustrations of the synchronous machine, induction machine and dc machine. If the teacher so desires, he may take up this portion along with the relevant machine chapters. Losses, efficiency, rating and cooling are touched upon briefly and from a general viewpoint.

Chapter 11 discusses dc machines with stress on motors. Armature reaction and commutation are discussed and so are the methods of excitation. Characteristics and speed control of shunt and series type dc motors immediately follow and are treated through the assumption of linear magnetization. Starting and efficiency are also touched upon.

The twelfth chapter discusses ac machines—both synchronous and induction machines. For the synchronous machine it is suggested that the teacher need follow only the heuristic treatment for the circuit model in the class. Experimental determination of synchronous reactance and its use in voltage regulation, synchronisation of a machine to mains and operating characteristics of the machine are covered here.

For the induction machine the circuit model is derived through ideas presented earlier and the concepts illustrated in the transformer. To save time, the teacher may skip the derivational steps and directly introduce the circuit model. Stress is laid upon the concept of power across the gap. The complete torque-speed characteristic and its dependence on rotor resistance is explained with the help of several solved examples. No-load and blocked rotor tests for parameter determination are also discussed. Methods of starting and speed control are briefly discussed. A short account is given of the double-cage induction motor. Some of the solved examples on induction motor may be taken up partly or completely ignored.

At the end, a brief descriptive chapter is devoted to single-phase induction and synchronous motors, servomotor, ac series motor and stepper motor.

As an aid to both students and teachers, the book gives as many as 110 typi-cally illustrative solved examples, and 204 unsolved problems with answers.

This book is based upon my experience of teaching similar courses and writing books in allied areas. My efforts have immensely benefitted from the opportunities for classroom experimentation provided by the flexible system of the Birla Institute of Technology & Science (BITS), Pilani.

I J Nagrath