Design of an electric machine is a challenging task, since it makes use of assumptions, approximations, empirical relations derived out of experience, etc., at the time of design. Conventional design is based on the above and optimality of any of the quantity such as cost, weight, efficiency cannot be expected since there is no guarantee of optimum values for the variables used in the equations. Optimization of a quantity is the act of obtaining best result under given circumstances. In order to optimize an objective, it is mandatory to use optimum values for the variables that appear in the objective function equation. The variables which appear in a d.c. machine are many and they are to be suitably tackled while designing. Hence, in this paper, obtaining optimum values for the main dimensions, namely armature diameter and armature core length are taken as objective, which will be useful for further design and improve performance of the machine. The power of the machine is taken as constraint for the optimization problem. The required equations are formed with the help of only two variables, which enables to go for a simple graphical method. A design problem is taken for illustration and designed to find the values for the main dimensions both by conventional and proposed graphical method. Improved values are obtained from graphical method compared to conventional method, which indicates optimum values for the variables. Further the values are obtained simultaneously, which is a special feature of the proposed graphical method. The results obtained are compared and analyzed. The optimality of the proposed graphical method is verified by popularly available optimizing method.
Armature diameter, armature core length, optimum values,, Graphical method, tangent
