Since the appearance of the second edition in 1989, the overall energy situation has changed considerably and this has generated great interest in non-conventional and renewable energy sources, energy conservation and management, power reforms and restructur-ing and distributed and dispersed generation. Chapter 1 has been therefore, enlarged and completely rewritten. In addition, the influences of environmental constraints are also discussed.

The present edition, like the earlier two, is designed for a two-semester course at the undergraduate level or for first-semester post-graduate study.

Modern power systems have grown larger and spread over larger geographical area with many interconnections between neighbouring systems. Optimal planning, operation and control of such large-scale systems require advanced computer-based techniques many of which are explained in the student-oriented and reader-friendly manner by means of numerical examples throughout this book. Electric utility engineers will also be benefitted by the book as it will prepare them more adequately to face the new challenges. The style of writing is amenable to self-study. The wide range of topics facilitates versatile selection of chapters and sections for completion in the semester time frame.

Highlights of this edition are the five new chapters. Chapter 13 deals with power system security. Contingency analysis and sensitivity factors are described. An analytical framework is developed to control bulk power systems in such a way that security is en-hanced. Everything seems to have a propensity to fail. Power systems are no exception. Power system security practices try to control and operate power systems in a defensive posture so that the effects of these inevitable failures are minimized.

Chapter 14 is an introduction to the use of state estimation in electric power systems. We have selected Least Squares Estimation to give basic solution. External system equivalencing and treatment of bad data are also discussed.

The economics of power transmission has always lured the planners to transmit as much power as possible through existing transmission lines. Difficulty of acquiring the right of way for new lines (the corridor crisis) has always motivated the power en-gineers to develop compensatory systems. Therefore, Chapter 15 addresses compensation in power systems. Both series and shunt compensation of lines have been thoroughly discussed. Concepts of SVS, STATCOM and FACTS have been briefly introduced.

Chapter 16 covers the important topic of load forecasting tech-nique. Knowing load is absolutely essential for solving any power system problem.

Chapter 17 deals with the important problem of voltage stability. Mathematical formulation, analysis, state-of-art, future trends and challenges are discussed.

MATLAB and SIMULINK, ideal programs for power system analysis are included in this book as an appendix along with 18 solved examples illustrating their use in solving representative power system problems. The help rendered by Shri Sunil Bhat of VNIT, Nagpur in writing this appendix is thankfully acknowledged.

Tata McGraw-Hill and the authors would like to thank the following reviewers of this edition: Prof. J.D. Sharma, IIT Roorkee; Prof. S.N. Tiwari, MNNIT Allahabad; Dr. M.R. Mohan, Anna University, Chennai; Prof. M.K. Deshmukh, BITS, Pilani; Dr. H.R. Seedhar, PEC, Chandigarh; Prof. P.R. Bijwe and Dr. Sanjay Roy, IIT Delhi.

While revising the text, we have had the benefit of valuable advice and suggestions from many professors, students and practising engineers who used the earlier editions of this book. All these individuals have influenced this edition. We express our thanks and appreciation to them. We hope this support/re-sponse would continue in the future also.

D P KOTHARI
I J NAGRATH