Question

Q5
(a) Briefly explain power system stability

Answer 1

Power System Stability:-

Power system stability involves the study of the dynamics of the power system under disturbances. Power system stability implies that its ability to return to normal or stable operation after having been subjected to some form of disturbances. Disturbances of the system may be of various types like sudden changes of load, the sudden short circuit fault, switching etc. From the classical point of view power system instability can be seen as loss of synchronism when the system is subjected to a particular disturbance.

The stability of the power system is mainly divided into three types depending upon the magnitude of disturbances: Steady state, transient and dynamic stability.

1) Steady-state Stability:-

Steady-state stability relates to the response of synchronous machine to a gradually increasing load. It is basically concerned with the determination of the upper limit of machine loading without losing synchronism, provided the loading is increased gradually.

2) Dynamic Stability:-

Dynamic stability involves the response to small disturbances that occur on the system, producing oscillations. The system is said to be dynamically stable if theses oscillations do not acquire more than certain amplitude and die out quickly. If these oscillations continuously grow in amplitude, the system is dynamically unstable. The source of this type of instability is usually an interconnection between control systems.

3) Transient Stability:-

Transient stability involves the response to large disturbances, which may cause rather large changes in rotor speeds, power angles and power transfers. Transient stability is a fast phenomenon usually evident within a few second.