Question

The inertia constant h of a machine of 200 mva is 2 p.U. Its value corresponding to 400 mva will be:

Answer 1

The new inertia constant of the system will be 1 PU

Explanation :

Given data;

Inertia constant of machine, Hm = 2

base rating of machine, Gm = 200 mva

base rating of system Gs = 400 mva

Inertia constant of the system, Hs = ?

We know that the product of inertia constant and base power rating is constant, i.e.

H x G = constant

=> Hs x Gs = Hm x Gm

=> Hs x 400 = 2 x 200

=> Hs = 1 pu

Hence the new inertia constant of the system on 400 mva base rating will be 1 PU