Question

A 50 Hz, 4-pole turbo generator rated 100 MVA, 11 kV has an inertia constant of 10 MJ/MVA. If the mechanical input is suddenly raised to 90 MW for an electrical load of 60 MW. Neglect mechanical and electrical losses. Then the rotor acceleration is ______electrical degrees /sec${}^2$.

• A. 270

Answer 1

The correct option is A 270
The rating of the machine, $G=100MVA$

Inertia constant, $H=10MJ/MVA$

Accelerating power, $P_a=90MW-60MW=30MW$

Angular momentum, $M=\frac{GH}{180f}=\frac{100\times 10}{180\times 50}=\frac{1}{9}MJ-s/electricaldegree$

Acceleration, $\alpha =\frac{P_a}{M}=\frac{30}{1/9}=270elec.degree/s^2$