In a 428 RPM, 25 MW horizontal hydrogenerator with a 40 ton rotor, the dc exciter armature has to be removed (due to new static excitation system). The dc exciter armature, weighing about one ton, is located inboard between the ODE sleeve bearing and the rotor spider.

Will removing this one ton exciter armature create dynamic unbalance at 428 RPM ? or worse, will it bring the critical speed towards the running speed?

The rotor spider dia/length is about 2.85 M/1.2 M and the exciter armature dia/length is about 1 M / 1.2 M. Distance between the bearings is 6.85 M. Shaft dia ODE - 500 mm and DE - 700 mm.

This message has been edited. Last edited by: edison123,

The unbalance will change with the amount that the exciter rotor has inherent and which is compensated in another plane. If there are correction in the rotor you remove, chance is that the change is small. Crit speed will increase a bit. I do not fear a problem, but it can be calculated. If you make a bump test now, hor and vert, you know where you stand. However, why remove the rotor at all. Cheaper to let it stay? Regards Arne

Thx Arnie. Exactly my advice - Let sleeping dogs lie. But, consultants + little knowledge = big issues. I am sticking with my advice. Let them eat cake.