An online technique for monitoring the insulation condition of AC machine stator windings

A novel online technique for monitoring the insulation condition of ac machine stator windings is proposed in this paper. The concept is to measure the differential leakage currents of each phase winding from the terminal box in a noninvasive manner to assess the insulation condition during motor operation. The conventional differential CTs used for phase fault protection can be replaced with high performance current sensors to measure the leakage current with higher accuracy. Indicators for insulation condition such as the capacitance and dissipation factor are calculated based on the measurements to provide a low cost solution for online insulation condition assessment. A simplified online insulation system model is derived for analysis and interpretation of the measured data. Experimental results on a 15-hp induction motor under simulated insulation degradation conditions show that the proposed technique is a very sensitive method capable of detecting incipient signs of insulation degradation.     

Novel high-speed induction motor for a commercial centrifugalcompressor

This paper describes the electrical, mechanical and metallurgical design, construction, and testing of a novel low-cost high-speed high-efficiency induction motor to drive a new type of small centrifugal compressor in industrial cooling applications. The 28-shaft-hp 50-kr/min motor features a unique laminated rotor with a multifunction high-strength copper-alloy cage brazed with a novel process. Relatively thin high-silicon steel laminations were used to achieve low losses and high mechanical strength at low cost, Different heat treatments for the stator and rotor laminations were used to optimize the mechanical and magnetic properties, The preprototype motors achieved about 94% (electromagnetic) efficiency at the rated point, including inverter harmonics, while meeting cost (less than one-tenth of aerospace practice) and produceability goals     

MASHA separator on the heavy ion beam for determining masses and nuclear physical properties of isotopes of heavy and superheavy elements

The MASHA mass spectrometer designed for identifying superheavy elements by their masses is described. The separation efficiency has been measured in the autonomous mode using four calibrated leakages of noble gases. The total separation efficiency of the mass spectrometer with a hot catcher and an ion source based on the electron cyclotron resonance has been determined using the ⁴⁰Ar beam. Test experiments have been carried out, in which α-active Hg isotopes produced in complete fusion reaction ⁴⁰Ar + ¹⁴⁴Sm → ^{184 ? xn} Hg + xn, have been detected in the focal plane of the mass spectrometer. The separation time and efficiency have been determined for short-lived Hg isotopes.     

Methods of Motor Current Signature Analysis

ABSTRACT

Recently a technique for monitoring and diagnosing mechanical problems, associated with rotating machines driven by electric motors, has been proposed and is now being offered by several commercial suppliers. This technique, known as “Motor Current Signature Analysis” or MCSA, seeks to apply much of the long experience in vibration signature analysis to the analysis of motor current in effect using the motor as a sensor akin to an acceleromeier This paper explores some of the history of the technique, presents several examples, and demonstrates a first order approach to the theory with associated cautions.     

Fatigue life of randomly loaded notched components

We generalize the results of the investigation of the fatigue life of structural components with notches under random loads. For this purpose, we analyze various blocks of random loads, both stationary and nonstationary, and their influence on the stress concentration near notches. An attempt is made to determine the critical sites of a structure according to the measured levels of strains on smooth surfaces. We propose a method for reducing stress concentration by applying localized plastic deformation of notches. This method is experimentally checked for specimens of low-carbon steel. In particular, it is shown that the realization of technological operations of this sort after long-term operation of a structure may significantly increase its safety. Institute of Materials and Machine Mechanics, Slovakian Academy of Sciences, Bratislava, Slovakia. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 5, pp. 75–86, September–October, 1998.     

Sensitive,On-Line Turn-to-Turn Fault Detection in AC Motors

Turn-to-turn fault detection is based on the principle that symmetrical (unfaulted) motors powered by symmetrical multiphase voltage sources will have no negative sequence currents flowing in the leads. A turn-to-turn fault will break that symmetry and give rise to a negative sequence current which may then be used as a measure of fault severity or to initiate protective action, such as a circuit breaker trip. A new way of looking at the effects of turn faults has been developed that improves sensitivity andspeedwhile reducing the probability of misdetection, taking into account voltage balance, load or voltage variation, and instrument errors. The method has been implemented on a PC and tested, in real time, with controllable faults in a small motor. Reliable detection of one shorted turn out of 648 turns per phase (in a Y-connected motor) was demonstrated with the fault indicator becoming fully developed in two cycles of line frequency after initiation of the fault.     

Diamond-Coated Laminations for High-Performance Motors

ABSTRACT

The high thermaJ conductivity and electrical resistivity of diamond make it an attractive material for enhancing heat transfer in the lamination stack of high-performance electric motors provided that it can be effectively and economically applied to the laminations. This brief study shows that, in principle, diamond core plate could double the radial thermal conductivity. Coating experiments, while not complete, show that many of the problems could be solved and that further development is warranted.     

An adaptive statistical time-frequency method for detection ofbroken bars and bearing faults in motors using stator current

It is well known that motor current is a nonstationary signal, the properties of which vary with respect to the time-varying normal operating conditions of the motor. As a result, Fourier analysis makes it difficult to recognize fault conditions from the normal operating conditions of the motor. Time-frequency analysis, on the other hand, unambiguously represents the motor current which makes signal properties related to fault detection more evident in the transform domain. In this paper, the authors present an adaptive, statistical, time-frequency method for the detection of broken bars and bearing faults. Due to the time-varying normal operating conditions of the motor and the effect of motor geometry on the current, they employ a training-based approach in which the algorithm is trained to recognize the normal operating modes of the motor before the actual testing starts. During the training stage, features which are relevant to fault detection are estimated using the torque and mechanical speed estimation. These features are then statistically analyzed and segmented into normal operating modes of the motor. For each mode, a representative and a threshold are computed and stored in a database to be used as a baseline during the testing stage. In the testing stage, the distance of the test features to the mode representatives are computed and compared with the thresholds. If it is larger than all the thresholds, the measurement is tagged as a potential fault signal. In the postprocessing stage, the testing is repeated for multiple measurements to improve the accuracy of the detection. The experimental results from their study suggest that the proposed method provides a powerful and a general approach to the motor-current-based fault detection     

Quantitative evaluation of induction motor broken bars by means ofelectrical signature analysis

The paper reports the comparison and performance evaluation of different diagnostic procedures that use input electric signals to detect and quantify rotor breakage in induction machines supplied by the mains. Besides the traditional current signature analysis based on one-phase current spectrum lines at frequencies (1±2s)f, the procedures based on analysis of the line at frequency 2sf in the spectrum respectively of electromagnetic torque, space vector current modulus and instantaneous power are considered. These last procedures have similar features and the comparison is developed on the basis of instantaneous torque. It is addressed that the speed ripple introduces two further terms in the instantaneous torque, decreasing the accuracy of the diagnosis. It is shown that there is a link between the angular displacement of the current sideband components at frequencies (1±2s)f. This allows a more correct quantitative evaluation of the fault and shows the superiority of the side band current components diagnostic procedure over the other proposed methods