Question

What is the formula for the checking of rigidity of induction machines?

(a) moment of inertia ≥ radius / length of stator core * 90

(b) moment of inertia ≥ radius * length of stator core * 90

(c) moment of inertia ≥ radius * length of stator core / 90

(d) moment of inertia ≤  radius / length of stator core * 90

This question was addressed to me in final exam.

This intriguing question comes from Frames of D.C. & A.C. Machines in portion Aspects of Design of Mechanical Parts of Design of Electrical Machines

Answer 1

Right choice is (c) moment of inertia ≥ radius * length of stator core / 90

For explanation I would say: The radius and length of the stator core along with the moment of inertia is calculated.  If the moment of inertia is greater than or equal to the product of length and radius divided by 90, the machine is more rigid.