Stability of Reluctance Motors from Freely Accelerating Torque Speed Curves

The limits of stability in reluctance machines are known to be narrow, especially in machines of improved design with high reactance ratio. These stability limits can usefully be investigated with the aid of computed and measured freely accelerating torque speed curves. The machine equations are developed using a frame of reference fixed with respeot to the rotor. Machine performance is then simulated on an analogue computer. A large number of freely accelerating torque speed curves are then generated for different values of machine parameters. The model is designed to cope simply with different motors and is based on a per unit system. All parameters can be simply varied, so that their effect on performance can be demonstrated . The torque speed curves that result can be said to be characteristic. of amachine with given parameters and contain information about starting torque, transient torque dips, synchronisation ability and stability. Since changes in parameters cause marked changes in shape of the freely accelerating torque speed curve, it is possible, by matching the results obtained from a practical test with those from a computer study, to determine where the total performance of the machine lies with respect to the optimum and to decide what changes are necessary to improve design.