Power system stability implies that its ability to return to normal or stable operation after having been subjected to some form of disturbances. From the classical point of view power system instability can be seen as loss of synchronism (i.e., some synchronous machines going out of step) when the system is subjected to a particular disturbance.

From the classical point of view power system instability can be seen as loss of synchronism (i.e., some synchronous machines going out of step) when the system is subjected to a particular disturbance. Three type of stability are of concern: Steady state, transient and dynamic stability.

The requirement of stability studies depends on the operating conditions of the industrial power systems. This sub clause is intended to summarize the so-called “things to look for” under different operating conditions and disturbance scenarios.

There are three types of power system stability: steady-state, transient, and dynamic. Steady-state stability, discussed in Chapter 5, involves slow or gradual changes in operating points. Steady-state stability studies, which are usually performed with a power-flow computer program (Chapter 6), ensure that phase angles across