• Journal of Magnetics
• /
• v.18 no.2
• /
• pp.117-124
• /
• 2013

Single-phase, brushless DC (BLDC) motors have unequal air-gaps to eliminate the dead-point where the developed torque is zero. Unfortunately, these unequal air-gaps can deteriorate the motor characteristics in the cogging torque. This paper proposes a novel design for a single-phase BLDC motor with an asymmetric notch to solve this problem. In the design method, the asymmetric notches were placed on the stator pole face, which affects the change in permanent magnet shape or the residual flux density of the permanent magnet. Parametric analysis was performed to determine the optimal size and position of the asymmetric notch to reduce the cogging torque. Finite element analysis (FEA) was used to calculate the cogging torque. A more than 28% lower cogging torque compared to the initial model with no notch was achieved.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.22 no.4
• /
• pp.801-810
• /
• 1998

Modeling and analysis of dynamic systems generally demand their resutls to be interpreted each other with a physical sense. It sometimes requires that there should exist a unified tool in the treatment of dynamic systems which can be applied to both their modeling and analysis equally. This paper shows how models just after the progress of modeling via bond graph standards are converted to ones which are appropriate for analyzing a dynamic system in the frequency domain. Four bond graph prototypes are introduced to obtain frequency properties of dynamic systems such as zero stability, relative order, zero and pole dynamics, etc. directly from bond graphs, and the method are proposed which reduces nearly all models of bond graph standards to one of the prototypes without any change of physical similarity. This procedure as a tool for the structural reduction of bond graphs and finding frequency properties of a dynamic system is further investigated to survey its effectiveness through an example.

• Proceedings of the KIEE Conference
• /
• 1991.07a
• /
• pp.86-89
• /
• 1991

In recent years, Vacuum Circuit Breaker(VCB) has been widely used to enhance the confidence and at the same time to ease maintenance of waterworks requipment as the power supply breaker of high voltage motor. When making and breaking the sources as VCB the powerful surge voltage, repetitive reignition phenomenon resulted from exceeding inter-pole endurance voltage of CB, has occured. It has transmitted to the winding of motor stator through the cable, and this surge voltage is repeated over and over again before finishing making and breaking action of CB according to cumulation of repetitive reignition surge, motor has become burned in the end. This paper describes surge voltage occuring in making and breaking of VCB as circuit parameters by transient phenonenon and examines closely the variance of peak values, wavefront-length, wavetail-length, when changing inductance and capacitance of a cable. Finally we will expect to protect motor winding breakdown from surge voltage through parallel connection of suitable-size in the motor.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.28 no.4
• /
• pp.21-28
• /
• 2014

Daily use characteristics of apparent power supplied to distribution transformer can be separated into two different time zone of waking hours and sleeping hours. In sleeping hours, using amount of power is decreasing. The actual curve of power seemed to be quite similar to this kind of separation. Inserting a condenser into a circuit in each different time zone led to maximize power factor of the transformer. The compensating condenser's on/off time is controlled by hysteresis circuit utilizing op amp and power factor of the transformer was improved from 0.945 to 0.999. As a result, the average of current reduction was 2.53A per hour of transformer.

• Transactions of Materials Processing
• /
• v.7 no.6
• /
• pp.610-619
• /
• 1998

The superplastic blow forming technology has advantages of cost reduction and low material consumption. compared to the conventional sheet metal forming technology due to the capability of precisely forming with high elongation and low flow stress. however it has a disadvantage that its partial thickness distribution is non-uniform. A processing technology like diaphragm forming has been developed even though it is difficult to prepare materials for superplastic blow forming. in this study a hemisphere forming of sheet before superplastic forming. It was found that the rotary forming material was less in quantity of cavitation at pole than that of hemisphere part that was superplastic formed without rotary forming treatment. Also discussed are the critical strain which is closely related to cavity shape and size.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.60 no.4
• /
• pp.739-745
• /
• 2011

This paper proposes a method for reducing the negative spatial harmonics of the radial flux density of an interior-type permanent magnet (IPM) motor. The reliability of the motor is increased by minimizing its vibrations under dynamic eccentricity (DE) state and normal state due to reduction of a negative spatial harmonics component through the influx of a zero spatial harmonics component in the radial flux density. To minimize the vibrations, optimal notches corresponding to the distribution shape of the magnetic field are designed on the rotor pole face. The variations of vibration computation by finite element method (FEM) and the validity of the analysis and rotor shape design are confirmed by vibration and performance experiments.

• Archives of Plastic Surgery
• /
• v.42 no.4
• /
• pp.438-445
• /
• 2015

Background Breast auto-augmentation (BAA) using an inferior pedicle dermoglandular flap aims to redistribute the breast tissue in order to increase the fullness in the upper pole and enhance the central projection of the breast at the time of mastopexy in women who want to avoid implants. The procedure achieves mastopexy and an increase in breast volume. Methods Between 2003 and 2014, 107 BAA procedures were performed in 53 patients (51 bilateral, 2 unilateral and 3 reoperations) with primary or secondary ptosis of the breast associated with loss of fullness in the upper pole (n=45) or undergoing explantation combined with capsulectomy (n=8). Six patients (11.3%) had prior mastopexy and 2 (3.7%) patients had prior reduction mammoplasty. The mean patients' age was 41 years (range, 19-66 years). All patients had preoperative and postoperative photographs and careful preoperative markings. Follow-up ranged from 6 months to 9 years (mean, 6.6 months). Results The range of elevation of the nipple was from 6 to 12 cm (mean, 8 cm). The wounds healed completely with no complications in 50 (94.3%) patients. Three patients had complications including 2 (3.7%) hematomas and 1 (1.9%) partial necrosis of the nipple-areola complex. Three (5.7%) patients were dissatisfied with the level of mastopexy achieved underwent a further procedure. No patient complained of scar hypertrophy. Conclusions BAA is a versatile technique for women with small breasts associated with primary or secondary ptosis. It is also an effective technique for the salvage of breasts after capsulectomy and explantation.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.6 no.2
• /
• pp.235-243
• /
• 1998

For motor operation at low speeds and loads, torque pulsation by the cogging torque is often a source of vibration and control difficulty. In this paper, the magnetic field of a motor is calculated by finite element method. The periodic cogging torque is determined using Maxwell stress method and time stepping method, and then decomposed using fourier series expansion, The purpose of this paper is to characterize design parameters on the cogging torque and to design a permanent magnet motor with a cogging torque less vulnerable to vibration, without sacrificing the motor performance. The design parameters include stator slot width, permanent magnet slot width, airgap length and magnetization direction. A new design with a less populated frequency spectrum of the cogging torque is proposed after characterizing individual effect of design parameters. Magnet pole edge shaping, by gradually increasing the cogging torque with reduced higher harmonics.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.6 no.4
• /
• pp.39-46
• /
• 1998

For permanent magnet brushless DC motors used for high speed fuel pumps, torque ripple is an important origin of vibration, acoustic noise and speed fluctuation. In this paper, the output torque profile of a PM motor with one phase energized is decomposed into the commutation torque, the reluctance torque and the armature reaction torque according to their source origins. It verifies that the output torque profile is qualitatively equivalent to the BEMF profile for low reluctance motors. This paper discusses the effect of magnet pole shaping and magnet arc length on the output torque and torque ripple. A magnet edge shaping is proposed to design a trapezoidal BEMF motor without torque ripple, with minimal sacrifice of the maximum output torque.

• Journal of Satellite, Information and Communications
• /
• v.1 no.2
• /
• pp.63-70
• /
• 2006

This paper presents the results of Ka band qualification model multiplexers for COMS Payload to be launched in 2008. These are the input and output multiplexers of the satellite transponder to use available frequency resources effectively and the diplexer of the satellite antenna to use the same reflector for both transmitting and receiving frequency bands, respectively. The input multiplexer with four frequency channels has four(4) independent channel filters which consist of an 8-pole elliptic band-pass filter for high frequency selectivity and a 2-pole equalizer for group delay equalization. For low insertion loss, mass and volume reduction, manifold type os employed for output multiplexer. E-plane T-junction is used for either splitting or combining a frequency band into two sub-bands. Asymmetric inductive irises are used to tune the receiving filter easily. The electrical performance and environmental test such as vibration test, mechanical shock test, thermal vacuum test and EMC test are performed and the results of all qualification model multiplexers are compliant to the requirement of each multiplexer. Followed by this qualification, the flight model equipment will be developed.