The arrival of cheap and fast microcomputers has stimulated the development of machine condition monitoring systems. Such systems measure one or more machine performance parameters, with a view to detecting the early signs of failure and initiating some form of action. To help developing these systems, a thorough knowledge of the behaviour of the machine in its post-fault condition must be well known and well understood. With this view in mind, a simple, yet reasonably accurate method of analysing the induction machine magnetic circuit under normal and abnormal conditions at moderate cost has been developed. Numerical field analysis is applied to the calculation of induction motors. It is based on a very simple Magnetic Network Technique (MNT) solution of the magnetic field. The field is assumed to be two-dimensional. The three dimensionality of the machine is taken into account within the two dimensional model. The general time-dependence of the field and the motion of the rotor are modelled correctly in a step-by-step solution. The model uses relatively small amount of computation time when compared with the previous methods of analysis. This technique is used for the evaluation of the broken bars effects on the machines performance and magnetic field variation. A series of experimental tests have been carried out. The results obtained are directly compared with the computed ones and they showed a good correlation. Finally, suggestions for suitable methods for the detection of broken bars are given along with some suggestions for future work.