Effect of Alternator’s Inertia Constant ‘H’ on Small Signal Oscillations in Power System

A Power System consists of the generating machines and transmission network in which the generating machine includes turbine, alternator and excitation system. Every synchronous generator has rotating rotor which has some inertia that depends upon the stored rotating energy in the system. There are various types of disturbances which are occurring on the power system. A stable power system should be designed such that it can withstand with the disturbances and remain in synchronism. The dynamic or small signal stability of an interconnected power system is its ability to return to normal or stable operation after subjected to some form of small disturbances. Dynamic instability is more probable than steady state instability. Small disturbances such as variations in loading, changes in turbine speed etc. which are small enough not to cause the system to lose synchronism but do excite the system into the state of natural oscillations. Machine inertia significantly affects the rate of rise and fall of system frequency. This paper discusses the effect of variation in machine inertia on the frequency of rotor oscillations. A Single machine infinite bus (SMIB) system is taken as the test system and its Eigen values are obtained by changing machine inertia constant.