Power system stability

POWER SYSTEM STABILITY

 Introduction

The stability of an interconnected power system is its ability to return to normal or stable
operation after having been subjected to some form of disturbance.
The study of stability is one of the main concern of the control engineer whose methods
may be applied to electrical power system.

Power system stability is classified into three, namely
(a) Steady state stability
This is primarily concerned with the ability of the system generators to remain in
synchronism after minor disturbances such as gradual load changes, changes in
excitation, line switching and so on.
(b)Transient stability
This is concerned with generators synchronism after a large or sudden disturbance such
as large load drop or addition, line switching, short circuit, sudden loss of big generating
(c)Long term stability
This forms the transition between transient and steady state stability.
(d)Swing curves
The swing curve is a plot of the rotor angle against time, and is used to determine
transient stability of a power system. A figure is used to illustrate the characteristics of a
system subject to disturbance.
(e)Equal area criterion
The equal area criterion is used to predict transient stability without solving the swing
equation for simple system such as one machine supplying an infinite bus-bar or two
machine systems.