Rotor-surface flux distributions in Lorenz-type medium-frequency inductor alternators

The paper considers the fluxes existing in the air gap of a single-phase Lorenz-type inductor alternator under load conditions. From the interaction of the field and armature reaction m.m.f.s with the rotor permeance, expressions are derived for the air-gap flux-density waves. These can be separated into (a) components stationary with respect to the rotor, resulting in distortion of the no-load waveform, which can be used to calculate voltage and load waveforms, and (b) components moving with respect to the rotor, of varying wavelength, which produce surface losses in the rotor. Experimental verification is given for the flux-density distribution under load, using search coils attached to the rotor surface of a 30kW model, making use of the heteropolar nature of the machine. The measurements of the load flux-density distribution are complicated by the presence of the nonsynchronous waves, which also generate signals in the rotor search coils. A novel method of interpretation of the search-coil signals is given that substantially eliminates the unwanted components. A computer program was used to synthetise the load flux-density curve from the no-load waveform using an angle ¿, which can be derived from a simple phasor diagram. It is shown to predict the load waveform under various conditions.