• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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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.

• 한국화재소방학회논문지
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• 제28권4호
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• pp.97-103
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• 2014

소방보호복은 고열유속에 의한 화상방지를 위해 3층 이상의 복합소재로 구성되어 있으며, 각 소재 사이는 공기 간극이 존재한다. 화재에 의한 고열유속 노출 시 공기 간극 내에서의 열전달은 대류와 복사에 의해 주로 발생하며, 그로 인해 간극의 크기에 따라서 비선형 특징의 열 저항 크기를 갖게 된다. 그러므로 본 연구에서는 보호복 소재 사이의 여러 가지 공기 간극(0~7 mm)에 대한 보호복의 열 보호성능을 자세히 파악하기 위한 실험을 수행하였다. 복사 열 유속 입사시에 시간에 따른 각 소재의 온도 변화뿐만 아니라, 열 보호성능을 가장 효과적으로 나타낼 수 있는 지표(Radiant Protective Performance, RPP) 값의 공기간극에 대한 변화 특성을 파악하였다. 공기간극이 증가할수록 단열효과가 커짐으로 인해 후면의 온도는 낮아지고, RPP는 커짐을 확인할 수 있었다. 특히 일정 열유속 조건에서 공기간극에 대한 RPP 값은 선형적인 특성을 나타내었고, 그러한 결과를 바탕으로 다양한 입사 열유속 및 공기 간극 조건에 대해 비교적 간단한 형태의 RPP 지표 예측 식을 제안하였고, 좋은 예측 결과를 얻을 수 있었다.

• Journal of Electrical Engineering and Technology
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• 제11권6호
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• pp.1614-1627
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• 2016

The purpose of this paper is to investigate the united Electromagnetic characteristics for the effective monitoring on the static air-gap eccentricity (SAGE) of turbo-generator. Different from other studies, this paper not only studies on the unbalanced magnetic pull (UMP) and the vibration characteristics of the stator and the rotor, but also investigates the harmonic features of the magnetic flux density and the circulating current inside the parallel branches (CCPB). The theoretical calculation, together with the finite-element-method (FEM) simulation and the experiment verification, is taken for a SDF-9 type non-salient generator. It is shown that, when SAGE occurs, apparent double-frequency UMP and vibrations will be produced both on the stator and the rotor, while the CCPB will have an obvious increment at the $1^{st}$ harmonic component. In addition, the amplitude of the magnetic flux density will be of cosine distribution in the circumferential position of the air-gap, while in normal condition it is a constant. Moreover, the pass-band amplitude, together with the $1^{st}$ harmonic of the magnetic flux density, will be enlarged as well. These united electromagnetic characteristics can be used as the diagnosis and monitoring criterion for SAGE.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제5B권1호
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• pp.34-38
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• 2005

The finite element method is very flexible for new shapes and provides flux distribution, magnetomotive force, eddy currents, and torques. However, it requires lengthy computational time in order to achieve desired accuracy. The magnetic equivalent circuit method takes less computation time than the finite element method. Therefore, the finite element method is mainly used to confirm the completed design. The magnetic equivalent circuit method is convenient for complicated analysis of the transient state of the induction motor. The magnetic equivalent circuit method is restricted to only one direction of magnetic flux. In this paper, the construction elements (that is, stator iron, rotor iron, yoke, air gap, etc.) of the squirrel cage induction motor were represented by a flux tube and the air gap magnetomotive force was calculated by the magnetic equivalent circuit method. Starting transient torque and phase current of the squirrel cage induction motor were verified by the theoretical calculation and the experiment.

• Journal of Electrical Engineering and Technology
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• 제6권5호
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• pp.666-670
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• 2011

In this paper, a method for detecting broken rotor bar and stator winding fault in a low voltage squirrel-case induction motor using an air-gap flux variation analysis is proposed to develop a simple and low cost diagnosis technique. To measure the leakage flux in radial direction, a radial flux sensor is designed as a search coil and installed between stator slots. The proposed method is able to identify two kinds of motor faults by calculating load condition of motors and monitoring abnormal signals those are related with motor faults. Experimental results obtained on 7.5kW three-phase squirrel-cage induction motors are discussed to verify the performance of the proposed method.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.95-97
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• 2006

Cogging torque is often a principal source of vibration, noise and difficulty of control in BLDC motors. Therefore, this paper will present a design method of magnetization system with sinusoidal air-gap flux density distribution of Nd-Fe-B magnets in ring type for reduction of Vibration and Noise and low manufacturing cost.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 추계학술대회 논문집 학회본부
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• pp.39-42
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• 1995

This paper analyzes air gap flux density of the induction motor with the rotor eccentricity and slot effects using Fourier series and FEM. We establishes the validity of results by analyzing the space harmonic order.

• 대한전기학회논문지
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• 제36권4호
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• pp.240-251
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• 1987

In this paper, with the end effect taken into consideration, the fundamental characteristics of a linear induction motor-the eddy currents of the secondary conducting sheet (traveller), the flux density in the air gap-are analysed by means of electromagnetic field theory. Accordingly, the derived governing eqations of the chatacteristics with goodness factor, presents that it was possible not only to predict the performance characteristics, but to obtain the data that needs to optimize a design of a motor with the reduction of the end effect.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제55권10호
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• pp.491-497
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• 2006

For high efficiency and easy speed control of brushless DC (BLDC) motor, the demand of BLDC motor is increasing. Especially demand of interior permanent magnet (IPM) BLDC with high efficiency and high power in electric motion vehicle is increasing. However, IPM BLDC basically has a high cogging torque that results from the interaction of permanent magnet magnetomotive force (MMF) harmonics and air-gap permeance harmonics due to slotting. This cogging torque generates vibration and acoustic noises during the driving of motor. Thus reduction of the cogging torque has to be considered in IPM BLDC motor design by analytical methods. This paper proposes the cogging torque reduction method for IPM BLDC motor. For reduction of cogging torque of IPM BLDC motor, this paper describes new technique of the flux barriers design. The proposed method uses sinusoidal form of flux density to reduce the cogging torque. To make the sinusoidal air-gap flux density, flux barriers are applied in the rotor and flux barriers that installed in the rotor produce the sinusoidal form of flux density. Changing the number of flux barrier, the cogging torque is analyzed by finite element method. Also characteristics of designed model by the proposed method are analyzed by finite element method.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.952-954
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• 2002

The effort for measuring the rotor vibration caused by the short of rotor winding or air-gap eccentricity has been carried on. This paper introduces on-line vibration monitoring technologies using search coils to measure flux for synchronous generators. A 3,300/6,600 (V), 150 [kW] synchronous generator is built, and search coils are designed and inserted in the wedges. Furthermore, air-gap eccentricity is analyzed by finite element method and compared with experiment tests. Induced voltages caused by different air-gap eccentricity on the search coils are compared as well.