• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.321-322
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• 2006

Faults on power systems are inevitable phenomena. These faults can be classified by two categories, temporary and permanent faults. Without distinction of fault types, the faults would induce several changes on power system such as transmission line trip. Especially, the most common phenomena which loads experience by the power system fault is voltage sag. Voltage sags mean that the bus voltage maintains under 0.9 p.u. of rating for several cycles, and they give serious effects to operation of load devices. To ensure proper operation of the load, the flywheel systems, one of the energy storage system, are suggested in this paper. This paper demonstrates the efficiency of flywheel energy storage system against voltage sag by PSCAD/EMTDC simulation.

• Progress in Superconductivity
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• v.10 no.1
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• pp.55-59
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• 2008

A Superconductor Flywheel Energy Storage System(SFES) mainly consists of a pair of non-contacting High Temperature Superconductor(HTS) bearings that provide very low frictional losses, a composite flywheel with high energy storage density. The HTS bearings, which offer dynamic stability without active control, are the key technology that distinguishes the SFES from other flywheel energy storage devices, and great effort is being put into developing this technology. The Superconductor Journal Bearing(SJB) mainly consists of HTS bulks and a stator, which holds the HTS bulks and also acts as a cold head. Static properties of HTS bearings provide data to solve problems which may occur easily in a running system. Since stiffness to counter vibration is the main parameter in designing an HTS bearing system, we investigate SJB magnetic force through static properties between the Permanent Magnet(PM) and HTS. We measure stiffness in static condition and the results are used to determine the optimal number of HTS bulks for a 100kWh SFES.

• Korean Journal of Agricultural Science
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• v.20 no.1
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• pp.68-87
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• 1993

Data acquisition system and computer program developed in this study could be well used in engine vibration analysis. The system and program developed were also operated to be able to control measuring interval, number of channels, number of data. The flywheel was specially studied to provide the proper weight with rubber damper for the engine design at low level of vibration. This study was conducted to obtain basic data which affect the engine vibration. The experiment of this study was performed on original weight flywheel, weight-reduced flywheel, weight-reduced and rubber-coated flywheel, weight-reduced and damper-attached flywheel. Avarage of peak value, maximum vibration, power spectrum density based on FFT analysis are major factors of this experiment. Results were obtained as follows : 1. When rubber was inserted in the flywheel rim of which weight was reduced from 32.2kgf to 24.4kgf, maximum vibration of the engine was decreased 48.3% at X axis, 35.5% at Y axis and 34.6% at Z axis in comparison with the flywheel of original weight. 2. When the flywheel of rubber damper was compared with the original flywheel, the average of absolute vibration for rubber damped flywheel was decreased at X, Y, Z axis and especially its decreasing rate was so high at X-axis comparing with the other flywheel, which implied that rubber damper was very useful to reducing the vibration of the engine at X axis. 3. Hysteresis losses of X, Y, Z axis were greatly decreased in the flywheel with rubber damper on rim. 4. Damped oscillation effect on X and Y axis vibration above average peak vibration by the flywheel of rubber damper on rim was larger than those by the other flywheels. 5. Power spectrums of vibration at real and imaginery part were bi-mode type. The vibration frequency of rubber dampered flywheel which weight is decreased was slightly increased as compared with original flywheel.

• Progress in Superconductivity and Cryogenics
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• v.3 no.1
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• pp.50-55
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• 2001

A new type of flywheel energy storage system that has a horizontal axle with High $T_c$, superconductor bearings using Y123 single-domained crystals was developed.The dynamic Properties, stiffness and damping of the high $T_c$, superconductor radial bearings were experimentally estimated using a imbalance excitation method. The imbalance excitation method applied to this rotor- bearing system identified the identified stiffness and damping of the high temperature superconductor beatings to be 2.8 $3.3 {\times} 10^5 N/m and 775 204$ Nsec/m respectively.

• Journal of KSNVE
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• v.9 no.5
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• pp.891-898
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• 1999

The purpose of Superconducting Magnetic Bearing Flywheel Energy Storage System (SMB-FESS) is to store unused nighttime electricity until it is needed during daytime. An analytical model of the SMB-FESS is necessary to identify the system behavior. At first, we have to model the superconducting magnetic bearing. Modeling the SMB is same as estimating the bearing parameter. The theoretical modal parameter is calculated through the equation of motion and the experimental modal parameter is estimated through the impact testing (modal testing). The bearing parameter is searched by using the non-linear least square method until the theoretical result corresponds to the experimental result. The suggested modeling method is verified by comparing experimental and analytical frequency response function.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.272-277
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• 1997

The axial bearing using two ring type permanent magnets to support the weight of a flywheel is proposed to reduce the bearing loss in a flywheel energy storage , system. Two permanent magnet makes stable force in axial direction but unstable force in lateral direction. The lateral unstable stiffness is identified quantitatively using flux analysis, and then through the rotor dynamic analysis on a rigid flywheel system the unstable effects on the system by the stiffness is investigated.

• Proceedings of the KIPE Conference
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• 2004.11a
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• pp.128-132
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• 2004

This paper proposed a control strategy for flywheel energy/recovery system with induction machine. The system is based on a vector controlled induction machine driving a flywheel and address the problem of regulating the DC-Link system voltage against input power shut-down. And we proposed the method to damp the oscillation of DC-Link. Experimental results are presented which verify the performance of the strategy.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.8
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• pp.717-726
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• 2010

For the application into a 1 kWh flywheel energy storage system(FESS), this paper presents the design scheme of radial and axial hybrid magnetic bearings which use bias fluxes generated by permanent magnets. In particular, the axial hybrid magnetic bearing is newly proposed in this paper, in which a permanent magnet is arranged in axial direction so that it can support the rotor weight as well as provide a bias flux for axial magnetic bearing. Such hybrid magnetic bearings consume very low power, compared with conventional electromagnetic bearings. In this paper, to stably support a 140 kg flywheel rotor without contact, design process is explained in detail, and magnetic circuit analysis and three-dimensional finite element analysis are carried out to determine the design parameters and predict the performance of the magnetic bearings.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.10
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• pp.99-106
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• 2008

5kWh FESS(Flywheel Energy Storage System) using AMB(Active Magnetic Bearing) has been under development and 1st trial system has been finished and run the operating test. Unfortunately, the test result was not satisfactory because FESS could increase the rotational speed up to 9,000 rpm only although the target rotational speed is 18,000rpm. It's because 1st bending mode frequency of flywheel shaft was too low and imbalance response was too big. To achieve the target speed, 1st bending mode and imbalance response must be improved and the whole FESS needed to be designed again. This paper presents the newly designed FESS and what has been changed from the 1st trial FESS to improve 1st bending mode and imbalance response. The experimental results to see how much 1st bending mode frequency was improved are presented, too.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.310-314
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• 1999

A prototype of Flywheel Energy Storage System with high Tc superconducting bearings was fabricated and tested to verify its applicability for the energy industry. The moment of inertia of assembled wheel with rotor magnets is about 1.072${\times}$10$^{-1}$ Kg-m$^2$. The wheel was designed to withstand its integrity up to the rotation speed of 20,000 rpm. YBCO bulk superconductors prepared by seed growth method were used as bearing to levitate and stabilize the rotating wheel. High speed rotation of the flywheel without mechanical contact was achieved by using specially designed Halbach type motor. The flywheel system showed very high stability during test operation performed up to the speed of about 10,000rpm. The energy loss measured by free decay test performed between 9,300 rpm and 7,000 rpm was calculated as about 45 W.