فهرست مطالب منصور اوجاقی

Many investigations have been conducted to detect single incipient faults in squirrel cage induction motors. However, there is much less research on detecting and discriminating simultaneous faults within the induction motor. The simultaneous presence of eccentricity fault with some other faults is unavoidable due to some manufacturing imperfections or the possible misalignment of the motor-load shafts. Neglecting the intrinsic eccentricity and simultaneous faults might cause mistakes in the condition motoring of the motor. This article presents an analytical and experimental approach to detecting the simultaneous mix of eccentricity and broken rotor bar faults. Theoretical analyses represented how the indicators appear in the stator current due to mechanical faults according to dynamic equations, MWFA, and Fourier series. Thus, a new frequency indicator was introduced to identify simultaneous faults. The suggestive index is monitored in the modified winding function (MWFA), and finite element (FE) simulations and its amplitude was studied in motors with healthy conditions and separate and simultaneous faults. Simulation and experimental results confirmed the capability of the proposed index to distinguish simultaneous faults from other cases. This method is non-invasive, low-cost, load-independent, and can be implemented in the monitoring system of any motor.

Due to the widespread usage of three-phase induction motors in various industries, including power plants, refineries, petrochemicals, mining, transportation, shipping, etc., requirements for monitoring their conditions to detect various incipient defects are increasingly growing. It is necessary to detect the induction motor faults, which may cause the motor to stop unintentionally, in the shortest time with the highest accuracy in order to eliminate the problem with prior planning before spreading it. Some effective indices for detecting different types of the rolling-element bearing localized faults are derived from the motor vibration signal. In this paper, the mentioned indices are measured and analyzed in different scenarios to evaluate their reliability using laboratory test results. The results show that the influence of the motor temperature in the range from 30 to 75oC on the magnitudes of the indices is between 1 to 3 dbs; considering the magnitudes of the indices, such influence is rather negligible. Similarly, increasing the motor load from no-load up to full-load can influence the magnitude of the best selected indices by up to 2 dbs. In addition, increasing the localized defect severity (the hole diameter) from 2 to 5 mm usually affects the indices magnitudes by an oscillating manner with a maximum oscillation amplitude of 20 dbs.

Induction motors play an indispensable role in setting up the industry’s wheel and production cycle. Therefore, much research is being done to improve their construction and production and to monitor their condition. This paper aims to study and investigate a common fault related to these motors, i.e. the oil whirl fault within their sleeve bearing, and try to provide a useful and effective solution in order to diagnose this fault. For this purpose, firstly, an induction motor that has one of its bearings with oil whirl fault, is modeled and simulated by appropriate definition of the air gap function and using the modified winding function approach. Then, the stator current is obtained under both the healthy and faulty conditions to detect an effective and non-invasive method for the fault diagnosis. The stator current signal is processed using a combination of the empirical mode decomposition and Hilbert transform, called Hilbert-Huang transform and a suitable index for detecting oil whirl fault is proposed. Then, the efficiency of the proposed index is evaluated by applying it to the stator current signal obtained from the practical induction motor and its efficiency is proved in practice.

Harmful impacts of oil whirl fault in sleeve bearing can be avoided by early detection of the fault. In this paper, after describing the oil whirl fault, an analytic approach is applied to determine frequency of the harmonics produced by the fault in instantaneous power waveform of induction motor. Then, using appropriate air gap function, winding function approach is used for simulating squirrel cage induction motor with bearing oil whirl fault. The instantaneous power spectrum, plotted using simulation results, approves creation of the proposed harmonics. These harmonics are also evident in instantaneous power of an induction motor that operates on oil pipe line, where vibration analysis shows presence of oil whirl fault in its bearing. Finally, the most appropriate harmonic as the oil whirl fault index is selected using simulation by considering their relative amplitudes as well as their sensitivity to the fault type, fault degree, motor load level and three-phase unbalance of the stator voltages.