Rotor Cage and Winding Fault Detection Based on Machine Differential Magnetic Field Measurement (DMFM)

This (patent-pending) paper presents a new method for detection of rotor winding intercoil short circuits of synchronous machines and slip rings induction machines, as well as rupture of rotor bars and cage ring of induction machines. It is based on differential measurement of magnetic field by using two measuring coils. Measuring the coil-induced voltage enables us to detect rotor winding faults, which means that measured voltage is approximately zero without fault and increases in the presence of fault. Analysis of the measuring signal enables us to detect and locate fault. This new method enables rotor winding fault detection with high sensitivity, which enables more reliable fault detection. In comparison with the motor current signature analysis method, this new method gives 200 times higher sensitivity to fault occurrence. Numerous finite-element (FE) simulations have been carried out to verify the method. Also, this method was experimentally validated via series of laboratory tests on the specially designed electric machines for fault study (broken rotor bars, broken ring and intercoil short circuit in a rotor winding). Additionally, this method is applied on more than 20 real machines in industry. This patent-pending method is already implemented in three innovative products placed on market, so this method is fully confirmed in practice.