Geared synchronous generator inertia constant H 1

[Carlos Melim]

Good evening everybody.

I want to calculate the inertia constant of a 1500 rpm synchronous generator with a 8304 rpm steam turbine prime-mover, both attached through a gear box.

I have the J figures for both. The generator has a J of 789 Kgm^2 and the turbine a J of 40 kgm^2.

I’ve come across the Equivalent moment of inertia concept. The constant inertia H the of generator alone is 0.9 seconds but, for the whole turbine-generator set, the H is around 2.3 seconds.

Some colleagues told me that for grid disturbances studies I should consider the generator alone.

That a steam turbine does not respond to a grid disturbance since its typical governor is slow.

Does it make sense? The governor can be slow but there is the synchronous inertial response of the generator that depends on the inertia constant of the set, right?

Am I missing something? The steam turbine is small but runs at a high speed so its inertia is not negligible.

I wish to hear your experts informations.

Thanks for your help.

 

[aussiejohn2]

G'day Carlos,
You are correct, your colleagues have it wrong. You need the total referred inertia (or inertia constant). Usually the gearbox, and often ancillaries like the exciter, coupling, and on small machines fan can be significant enough to include. The total mass is accelerated. And for the studies where inertia is important (large-disturbance stability), steam turbine governor response is certainly significant and *does* need to be included.

I am uncertain about your numbers - on the (larger - no gearbox) STs I am familiar with i think the turbine (particularly LP) dominates the inertia.

JD.