Detection of Eccentricity Faults in Induction Machines Based on Nameplate Parameters
ABSTRACT Eccentricity-related faults in induction motors have been studied extensively over the last few decades. They can exist in the form of static or dynamic eccentricity or both, in which case it is called a mixed eccentricity fault. These faults cause bearing damage, excessive vibration and noise, unbalanced magnetic pull, and under extreme conditions, stator-rotor rub which may seriously damage the motors. Since eccentricity faults are often associated with large induction machines, the repair or replacement costs arising out of such a scenario may easily run into tens and thousands of dollars. Previous research works have shown that it is extremely difficult to detect such faults if they appear individually, rather than in mixed form, unless the number of rotor bars and the pole-pair number conform to certain relationships. In this paper, it is shown that the terminal voltages of induction machines at switch-off reveal certain features that can lead to the detection of these faults in individual form, even in machines that do not show these signatures in line-current spectrum in steady state, or to the detection of the main contributory factor in case of mixed eccentricity.
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ABSTRACT: Abstract—This work shows a method to quantify rotor eccentricities in synchronous machines by exploiting the unbalance caused in the split-phase currents. The paper first develops a machine model comprehensive of eccentricities and parallel circuits in the stator, by using symmetrical components. Then, the model is used for formal calculation of the unbalanced currents. Finally, the equations are reversed to obtain eccentricity degrees from current measurements. Practical formulas are given for fault assessment, only requiring machine line voltage and synchronous reactance. The method can be applied on load. This paper provides full details of the theory underlying the method. The theory also clarifies some aspects about split-phase currents, not deepened before. It is proven that the air gap flux modulation due to eccentricities, acting through additional 2(p±1)- pole flux waves in 2p-pole machines, stimulates additional currents which circulate in the stator and turn into 2(p±1)-pole rotating space-vectors in the complex domain. Vector trajectories have shape and amplitude dictated by eccentricity type and degree, respectively. This study is limited to 2p-pole machines with p≥2. The theory is corroborated by simulations of a practical 1950kVA generator in this Part I. Experimental proofs and simulations of a laboratory 17kVA machine are provided in Part II of the paper.IEEE Transactions on Industrial Electronics 08/2014; 61(8):4193-4205. · 5.17 Impact Factor
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ABSTRACT: Many papers are available in the literature about detection of faults in induction machines. However, they generally deal only with a single fault. Instead, in practice, the case of mixed faults is quite common: the simultaneous presence of broken rotor bars and an intrinsic eccentricity or a coupling misalignment occurs often in an induction machine. The aim of this paper is to analyze theoretically and experimentally the stator current of an induction machine operating with mixed faults: broken rotor bars and static eccentricity (SE). First, an analytical expression for the mutual inductances under SE is derived using a mixture of modified winding function and Fourier series approach. Then, both theoretical and simulation studies are presented to show how the stator current is influenced by the simultaneous presence of (SE) and broken rotor bars with the consideration of the speed ripple effect. It is demonstrated that, in addition to the well-known characteristic frequencies of broken bars, and the rotor slot harmonic (RSH) used for the detection of (SE), this kind of mixed fault introduces in the stator current a series of additional harmonics, in the form of sidebands centered around the fundamental and RSH. More important, it is shown that some of these harmonics are similar to the frequencies introduced by the mixed eccentricity. Finally, experimental results have been presented to validate the analytical and simulation results.IEEE Transactions on Industrial Electronics 01/2014; 61(5):2452-2463. · 5.17 Impact Factor
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ABSTRACT: The fault diagnosis of rotating electrical machines has received an intense amount of research interest during the last 30 years. Reducing maintenance costs and preventing unscheduled downtimes, which result in losses of production and financial incomes, are the priorities of electrical drives manufacturers and operators. In fact, both correct diagnosis and early detection of incipient faults lead to fast unscheduled maintenance and short downtime for the process under consideration. They also prevent the harmful and sometimes devastating consequences of faults and failures. This topic has become far more attractive and critical as the population of electric machines has greatly increased in recent years. The total number of operating electrical machines in the world was around 16.1 billion in 2011, with a growth rate of about 50% in the last five years .IEEE Industrial Electronics Magazine 06/2014; 8(2):31-42. · 3.76 Impact Factor