Non-Synchronous Operation of a Hysteresis Machine

Abstract

A detailed study is made of the field distribution in a hysteresis machine, having a mechanically rotated magnetic field, for non-synchronous speeds. A qualitative theory of operation is developed and the Poynting vector concept of nett power flow used to predict the torque-excitation characteristic. Constructional details of the experimental machine are given and the tests performed for the measurement of torque and magnetic flux density are described. A comprehensive interpretation of the magnetic flux density waveforms is given, with special regard to those obtained in the non-magnetic regions. To demonstrate the significance of the low relative permeability of the rotor active material alone, experiments with a non-metallic, non-magnetic rotor and on analogue models are conducted, and verified analytically. In the light of these results, the spatial hysteresis effect of the rotor on the field distribution is discussed. The qualitative theory brings out clearly the physical operation of the machine. It establishes a new concept of ‘independent' rotor magnetisation, derived from the permanent magnet properties of the rotor, as the connecting link between the rotating magnetic field and the production of torque. The spatial hysteresis effect on the airgap magnetic field is explained by reference to this rotor magnetisation. Poynting's theorem is applied to calculate the power flow in the machine. The developed torque is obtained as the difference between the nett power flow in the airgap and arbor regions of the rotor. This eliminates the necessity of. measuring the magnetic field components within the rotor magnetic material. The calculated torque—excitation curve shows satisfactory correlation with the measured characteristic.