CURRENT MEASUREMENTS AND ANALYSIS FOR INDUCTION MOTOR DIAGNOSTICS

Additional motor vibrations are the result of a fau lty bearing. They are reflected in the harmonic content of stator currents. The object of the investigation presented in the paper are measurements related to diagnosti cs of induction motors, especially damages caused to bear ings. Due to the fact that the amplitude of the net work voltage basic harmonic in the current spectrum is high in comparison with components responsible for damages of bearings, preliminary elimination of this compon ent from the analog current signal has been propose d. The problem with interpretation of diagnostic measu rements in pr esent systems is the difference between measurement results of characteristic frequencies a nd theoretical calculations. In the proposed measurement system this problem was solved in such a way that the value of the angular speed and of the supply frequenc y is calculated on the basis of appropriate compone nts in the very same current spectrum that is further used in the search for dia gnostic components. The paper presents also the measuring system and pr ovides results of the investigations carried out on a motor encumbered with a specially prepared defect.