What I understand is that: the total inertia of the power system is constant and depends mainly on the number of committed synchronous generators; high number of connected generators means high inertia. few number of connected generators mean low inertia.
why there are many papers try to calculate and estimate the system inertia?
Hello Shraf Eldin Sati ,
Forgive my ignorance, but I thought knowing the system inertia was necessary for stability analysis via the swing equations of the various synchronous machines in the system. Because of the complexity of examining system stability algebraically, I thought that the usual approach was to combine several machines together, which were assumed to approximately swing together, in a bid to make the solution of the stability problem more manageable. Even if, as you say, the total inertia is constant, don't you still need to know the values of the individual inertias for the full-up analysis, or the values of the combined inertias for the condensed analysis? I mean, don't you need to be able to generate numbers from your analysis? If you don't know the inertias how do you get to the numbers?
Or are you saying that we should simply get the inertias from the nameplates of the various machines instead of trying to estimate them from the behavior of the system as a whole?
Perhaps I do not understand your question, in which case, please, ignore my ramblings.
Regards,
Tom Cuff
Thomas Cuff; I mean, we can calculate the total system inertia by summing individual generators' inertia as the generator's inertia does not change. So H total = sum(H of all generators). So why do we need to estimate the inertia if it can be calculated?
Hi Shraf Eldin Sati ,
The inertia constant, H, is, in fact, not constant, see [1]. Since H is a nonlinear function of some of the machine parameters, see [1], it may be that for a system of machines, the totality of the system behavior may be greater or less than the sum of its individual behaviors, i.e., superposition may not work: Hsystem≠ΣHi. Perhaps the papers you have consulted are simply trying to model the system of machines as one or two machines, and the H they are estimating is a composite value or set of values.
[1] Edward Wilson Kimbark; Power System Stability, Volume 1; John Wiley & Sons, Inc.; 1948; p. 25.
In addition, it is not clear to me, even in the case of one machine, that you can derive its H from first principles, i.e., without extensive modelling and curve fitting.
I am sure one of the RG members can provide you with a better answer so I will step aside.
Regards,
Tom Cuff
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