Power System Stabilty : Basic Concepts and Important Terms

This article deals with the basic concept of power system stabilty and types of power system stability like steady state stability, transient state stability and transient stability limit etc.

Power System Stability


The term stability is closely related with synchronism. Synchronous generators or alternators and synchronous motors have a tendency to remain in synchronism or in step with each other. During system disturbance such as sudden increase in load, sudden switching, power swings etc. The synchronous machines experience oscillations of torque angle about the mean position. However, the synchronous machines have inherent tendency or maintaining synchronism. Loss of synchronism is called loss of stability.

What is stability ?


Ability of synchronous machine or part of a system to develop restoring forces equal to more than disturbing forces so as to remain in synchronism is called stability.
The disturbance may be sudden or the change in load may be very gradual. Accordingly, there are two distinct terms called transient stability and steady state stability.
The term steady state stability refers to ability of a system or its part to respond to small, gradual change in power at a given point of the system. Steady state stability limit is the maximum possible power that can be transferred at a given point of the system without loss of synchronism, with very gradual increase in power.
The term transient stability limit refers to the maximum possible power that can be transferred at a given point of the system without loss of synchronism for given sudden large change in power.
The concept of stability can well be explained by means of two machine system. The system is used as a conceptual aid.

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