CAPACITANCE CALCULUS OF A BEARING

[logic5]

I would like to calculate theoretically the capacitance of a bearing with metallic rings and ceramic spheres (see

http://www.alibaba.com/catalog/10516334/Ceramic_Bearing_Balls.html).

The expression for a cylindrical capacitor is: (2*pi*eps0*l)/(lnb/a).

However, when adding some spherical balls inside the cylinder, how should I proceed?

Thank u,

logic