Stevenson J. Power system analysis

CHAPTER

BASIC

CONCEPTS

Normal and abnormal conditions of operation of the sys tem are the concern of

the power system engineer who must be very familiar with steady-state ac

circuits, particularly three-phase circuits. The purpose of thi s chapter is to

review a few of the fund3mental ides of such circuits; to establish the notation

used throughout the book; and to introduce the expression of values of voltage,

current, impedance , and power i n per unit. Modern power system analysis relies

almost exclusively on nodal nerwork representation which is introduced in the

form of the bus admittance and the bus impedcce matrices.

1.1 INTRODUCTION

The waveform of voltage at the buses of a power system can be assumed to be

purely sinusoidal and of constant frequency. In developing most of the they in

this book, we are concerned with the phasor representations of sinusoidal

volt?ges and currents and use the capital letters

and

to indicate these

phasors (with appropriate subscripts where necessary). Vertical bars enclosing

and I, that is, I VI and I

I, designate the magnitudes of the phasors. Magnitudes

of complex numbers such as impedance

and admittance Yare also indicated

by vertical bars. Lowercase letters generally indicate instantaneous values.

Where a generated voltage [electromotive force (emf)] is specied, the letter E

rather than V is often used for voltage to emphasize the fact that an emf rather

than a general poten tial di