Designing Switched Reluctance Generators: The Machine Constant and Choice of the Main Dimensions

Abstract

The approach to designing electrical machines involving the use of a machine constant has been applied for already more than a century. By using the machine constant, the designer can select the volume of active parts for a machine of the preset capacity and rotation frequency proceeding from the chosen electromagnetic loads. Given the known volume of the machine active parts, the machine main sizes can be determined in a quite straightforward manner. A bank of machine constant values has been set up based on the experience gained for many years of engineering activities, which is used for designing electrical machines of conventional types. The conventional machine constant depends not only on the electromagnetic loads, but also on the machine mechanical design, applied materials, cooling system type, and a number of other factors. However, the conventional machine constant cannot be used in developing new designs of electrical machines, nor can it be used for comparing the characteristics of electrical machines of different types. The machine constant is defined as the ratio of the volume of machine active parts to the machine torque (the machine specific volume) and can be used for comparing machines of different types provided that the effect of design factors on its value is excluded. A new machine constant is proposed, in which the magnetic field strength in the machine air gap is used instead of the conventionally used electric loading. The proposed machine constant can be applied in designing machines of different types and for comparing the specific parameters of electrical machines, including their design modifications. Theoretical investigations and engineering calculations were carried out, the results of which were used to obtain the dependences of machine constant for reluctance machines having different tooth geometries and at different electromagnetic loads. It is shown that the proposed machine constant remains almost unchanged in a wide variation range of the reluctance machine tooth zone relative parameters at identical electromagnetic loads.