Effects of external yoke and clamping-plates on AC motor external field

This study focuses on the external flux in the vicinity of AC electrical rotating machines. The influence of the external housing, constituted of the external yoke and the clamping-plates, is studied with a finite-element modelling, an analytical model and experimental measurements. Two induction machines are analysed; the first is equipped of an external yoke made of cast iron, whereas the second is made of aluminium. Those machines have been instrumented with magnetic flux sensors placed each side of the flanges and each side of the external yoke border. The conclusions of this study have a double interest. On the one hand, they can be used to understand what the influence of the external housing in the flux transmission is. That allows using the external magnetic flux as information to diagnose the rotating machines. On the other hand, the study can help machine designers to define motors with a discreet magnetic signature.