Evaluation of the voltage supply unbalance and detection of the short-circuit faults in induction machine through the neighboring magnetic field

This paper presents a new way to use magnetic field analysis for the detection of two electrical dissymmetries which appear in the asynchronous machine. The magnetic field is an interesting variable to exploit for the diagnosis of electrical machines because its measurement is easy, completely noninvasive, and uses inexpensive coil flux sensors. The advantage to use this variable is that it is more sensitive to electrical faults than to current or vibration. In the faulty case or voltage supply unbalance, a magnetic dissymmetry occurs which can be found in the external magnetic field measured near the electrical machine. The sensitive harmonics are extracted from the signals delivered by a pair of flux sensors placed around the machine and the data obtained from several positions are analyzed. The amplitude ratio and the correlation coefficient are the parameters used by the proposed diagnosis method. In practice, the user needs to detect whether there is a fault but also to know its origin. The originality of the proposed method is that can detect and classify the type of fault at the same time. The tests are applied for unbalance voltage and short-circuit faults. Obtained results show that the proposed approach makes it possible to detect and to determine the type of fault and for an easy analysis a graphic interpretation is proposed. Thus, the results presented in this paper pave the way to the better classification of different types of faults that appear in electrical machines and so to ensure safe operation in various technical processes