A proposed procedure for interpole winding design

This paper proposes a means of deterministically calculating the interpole strength of a DC machine. This is done by considering the DC machine as a primitive slip ring machine to obtain the voltage equation for the armature coil undergoing commutation. From this equation, an expression describing the current in this coil during the commutation event is obtained. The reason for deriving this expression is to determine what the current in the coil undergoing commutation will be at the end of the commutation period. In order to apply this expression, it is necessary to obtain values for the various inductances and rotational inductances that make up this expression. It is shown how finite element analysis is applied to obtain these quantities. One of the rotational inductances obtained from finite element analysis and used in this expression, is dependant on the number of interpole turns. By considering the conditions at the end of the commutation period, it is shown how the correct number of interpole turns can be determined for perfect commutation. The method is verified by applying the technique to a number of machines whose commutation is known to be adequate.