• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.825-826
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• 2006

This paper describes the effects of air gap eccentricity in induction machines. Asymmetric electro-magnetic force caused by the frictional worn bearing, rotor misalignment and unbalanced rotor etc. generates an asymmetrical operation, vibration and electro-magnetic noise. In this paper, we focus on investigating the asymmetrical operation considering of unbalanced magnetic force in squirrel-cage induction motor with 380 [V], 7.5 [kW], 4P, 1,768 [rpm]. The effects of the rotor eccentricity, magnetic force are investigated by finite element method (FEM) and experiment. The results can be useful for on-line monitoring of an induction motor.

• Proceedings of the KIEE Conference
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• 1999.07a
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• pp.67-69
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• 1999

This study deals with the unbalance response of a rotor of Switched Reluctance Motor(SRM) due to unbalanced mass. The method to analyze SRM with rotor-bearing system is based on an extension of the well-known Transfer Matrix Method(TMM). Most of the calculation results present the natural frequencies as a function of the speed of rotation which yields critical speeds and response to unbalanced mass.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.9
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• pp.499-508
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• 2002

This paper presents a finite element analysis of the electromechanical field in the spindle motor of a computer hard disk drive considering the speed control and mechanical flexibility. The driving circuit equation is modified by considering the switching action of PWM inverter, and is coupled with the Maxwell equation to obtain the nonlinear time-stepping finite element equation for the analysis of magnetic field. Magnetic force and torque are calculated by the Maxwell stress tensor. Mechanical motion of a rotor is determined by a time-stopping finite element method considering the flexibility of shaft, rotor and bearing. Both magnetic and mechanical finite element equations are combined in the closed loop to control the speed using PWM. Simulation results are verified by the experiments, and they are in food agreement with the experimental results.

• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.801-803
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• 2003

Faults in induction motors can be categorized into mechanical faults and electrical faults, and most mechanical faults result from inferiority or damage of the bearing, while most electrical faults derive from insulation faults of stator windings and rotor bar cracks. When a crack appears on the rotor bar, its efficiency decreases, which increases energy consumption and temperature, reducing the life span of the motor. This kind of fault can only be sensed by the protection relay after the condition has worsened to a certain degree, bringing massive economic loss. This paper will deal with the diagnosis method of rotor bar faults through the load current analysis method of the motor used during operation.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1057-1058
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• 2007

This paper proposes an alternative vibration detection method in a squirrel-cage induction motor using flux sensors. The air-gap flux will be changed when mechanical vibration occurs by bearing fault as well as broken rotor bar and air-gap eccentricity. For detecting those flux variations due to vibration, search coils are installed at stator slots. The induction motor with 380 [V], 7.5 [kW], 4 [Poles], 1,760 [rpm] ratings is used. Magnitudes and distortion of the induced voltage from flux sensors are used to discriminate faulted types. As a result, the flux sensor has been proven to be useful for vibration detection. It is compared to the result with vibration sensor as well.

• Proceedings of the KSR Conference
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• 1998.11a
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• pp.329-336
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• 1998

The characteristics of vibration and sound signals which occurs at the driving system of electric train are investigated in this study since the vibration of driving system is one of the main sources of vibration and sound in electric train. The vibration signals are changed its signal patterns during the transmission from the source to passengers due to noise or several unknown factors. To avoid the complexity of actual signals of electric train, signals from experimental apparatus of motor/gear driving system are analyzed to find the appropriate method of analysis and to characterize the signal patterns. The used methods are waterfall diagram, transfer function and modal analysis. The results shows that the vibration signals are usually originated from motor bearing and gear meshing and these signals are transmitted to bottom or bogie. Also, the sound signal is similar to the vibration of bottom or bogie, but it is not so clear to figure out the source of vibration.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.10a
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• pp.171-172
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• 2012

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.879-884
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• 2007

Flywheel energy storage systems have advantages over other types of energy storage devices in such aspects as unlimited charge/discharge cycles and environmental friendliness. In this paper we propose a millimeter scale flywheel energy storage device. The flywheel is supported by a pair of passive magnetic bearings and rotated by a toroidally wound electric motor/generator. The geometry of the bearings is optimized for the maximum dynamic performance.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.307-311
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• 1997

This paper describes influence of thermal deformation on nosic characteristics in high speed spindle systems. Heat generation in front, rear spindle bearings and built in motor lead to diverse thermal deformation of headstock with time. This deformation changes assemble tolerance in bearing housing, especially to elliptic form. The elliptic assemble tolerance generate high nosie level with dominant amplitude in double rotational frequency.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.452-457
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• 1998

This paper deal with problems of leakage current, shaft voltage, bearing current, and EMI, in valiable-speed AC drives. The originating mechanism is illustrated with a high-frequency equivalent circuit. Reduction methods are classified in to six categories based on the equivalent circuit. Some experimental results show that a common-mode transformer (CMT) and a common-noise canceler (ACC) can solve the problems, which have been proposed the authors.