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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 inter-coil 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 to detect rotor winding faults. That means that measured voltage is approx. zero without fault and increases in presence of fault. Analysis of the measuring signal enables 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 (MCSA) method, this new method gives 200 times higher sensitivity to fault occurrence. Numerous Finite element (FE) simulations has 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 inter-coil 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.

finite element ; inter–coil shorted turns ; rotor cage faults ; induction machine ; synchronous generator ; rotor bars

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