The synchronous reactances of a salient-pole synchronous machine are functions of the load of the machine because of the non-linearity caused by magnetic saturation. In the d-axis the machine is more saturated than in the q-axis, and for exact analysis appropriate saturated reactances have to be used. A three dimensional numerical solution of the field problem, based on network method is developed to calculate the reactance. The non-linearity of the magnetic materials, the complicated contours of the cross section of the machine, and the currents in the various windings are fully considered. The analysis is applied to the predetermination of flux and flux density in a homopolar linear synchronous machine. The flux densities are used to predict the magnetising inductances, by the use of a flux linkage method. The normal forces acting between the rotor and stator are also calculated in a number of different ways including the use of Maxwell's stress. The field is described and the simplifying assumptions arid boundary conditions are discussed. The governing equations for scalar potential in terms of network properties are developed from Maxwell's equations. The numerical solution of the linear set of network equations is obtained by successive over-relaxation and the nonlinearity is considered by an alternating relaxation procedure. The difficulties associated with the use of scalar potential have been overcome by considering the permeable region to be current free. All the current-carrying conductors are placed in the surrounding air. Equations for a simple air-gap calculation of the inductances and normal forces in a homopolar linear synchronous machine are derived. The leakage inductances produced by air-gap flux which fails to reach the rotor have been considered as parts of the magnetising inductances. Inclusion of these leakage components enables close agreement to be obtained with the measured voltages. The leakage components have no influence on the forces produced by the homopolar LSM. The good agreement achieved in a comparison between the calculated and experimental results for the homopolar linear synchronous motor, confirms the validity and accuracy of the network field calculation method. The mechanical and electrical characteristics of the homopolar LSM are compared with those already found for a heteropolar machine. The advantages and disadvantages of both these machines for advanced transport system are discussed in details. Methods for improvement of power factor and for reducing pole losses are also mentioned.
|Date of Award||1984|