Research On Rotor Broken Bar Fault Diagnosis Of Induction Motor With DC Injection

A motor failure not only can result in damage to the motor, but also can result in unscheduled machine downtime and the shutdown of a production line, which will cause heavy financial losses and catastrophic failure. Statistical studies have shown that the rotor broken bar fault, which account for nearly 10% of total induction motor failures, is the most familiar fault for induction motors. Consequently, researches on rotor broken bar fault diagnosis able to detect this kind of fault at an early stage and also to allow for carefully planed repair actions are of great theoretical significance and socioeconomic benefits. Firstly, the principle of injecting a small DC signal into line-connected induction machines for diagnosis of rotor faults is proposed in this paper. Then, the feasibility and validity of testing rotor broken bar fault based on twice PQ transformation and Extended Park's Vector Approach is verified.The equivalent DC injection is not actually injecting a dc bias into the stator winding, but causing the voltage drop across the circuit to be asymmetrical by means of the asymmetrical resistance in a period. Under DIM (DC Injection Mode) , when there is a fault in the rotor, therewill be conspicuous frequency component at 2(1-s)f_s Hz which is far away from the main frequency in the spectrum. The main task of this paper is to detect the rotor broken bar fault by means of extracting and describing the conspicuous frequency component at 2(1-s)f_s Hzquantificationally.With the positive sequence fundamental voltage components and its minus Hilbert transformation as elements, the new PQ transformation matrix is constructed and the rotor broken bar fault diagnosis method based on the twice PQ transformation is presented. And the results obtained from laboratory size motors demonstrate the effectiveness of the proposed technique, for detecting broken rotor bars in operating three-phase induction machines.This paper also introduces another new approach, based on the spectral analysis of the motor current Park's Vector modulus, for detecting the occurrence of rotor cage faults in operating three-phase induction machines. The major theoretical principles of the Extended Park's Vector Approach are described. Laboratory test results demonstrate how the presence of rotor cage faults can be effectively detected by the application of this new approach.. These results are also correlated with the ones obtained by the conventional motor current spectral analysis and by the classic Park's Vector Approach.