• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1894-1895
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• 2007

It is excitation system for nuclear emergency generator that is to startup automatically and sequentially supply essential loads with power. There are static type and alternating exciter, etc in its excitation system. An object of study is static excitation system which power is taken from power potential transformer and power current transformer. It is to complement curtailment of excitation system ability at happening short accidents. And Startup mode are quick startup and slow startup, etc. Its characteristic is looked into in this paper.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.3
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• pp.624-631
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• 2011

In this paper, the RCF method is used in sensitivity analysis problems of the discrete power systems including both series FACTS equipments such as TCSC in transmission lines and generator controllers such as Exciter and PSS in generator terminal. To apply the RCF method in small signal stability problems of discrete power systems, state transition equations of controllers and TCSC are derived and the sensitivity calculation algorithm using state transition equations in discrete time domain is devised. The results of eigenvalue analysis showed that the variations of eigenvalues after periodic switching operations of TCSC can be calculated exactly by the RCF method and the change of firing angles in TCSC have important effect to determine the stability of power systems.

• Proceedings of the KIEE Conference
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• 1998.07f
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• pp.2024-2026
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• 1998

Many power plants built 20-30 years ago are facing problems associated with the excitation system used for controlling generator output voltage. After years of reliable operation, generation is experiencing increased down time due to maintenance associated with the exciting excitation equipment. Reliability of the excitation system has become an issue, especially where many of these generation plants may be critical to the internal processes used for manufacturing. Wear out mechanisms such as those associated with the wire wound rheostat the electromechanical voltage regulator, insulation failures of the rotating exciter and commutator deterioration have become real problems typical of many older installations. These are some of the issues that are affecting system reliability for older power plants. This paper will address typical problems associated with the old excitation systems and the justification for a replacement static excitation system used in many Paper Mills.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.294-296
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• 1995

In this paper, a vector control method for a AC-Excited BLSM(Brushless Synchronous Motor) is proposed. The BLSM has a feature that separate exciter is not needed for excitation. The proposed method is described in two parts as follow, one is the design of drive and the other is a modeling for its implementation. Rotor flux is estimated using indirect sensing method based on voltage equation in the synchronously rotation reference frame. And rotor position is calculated from rotor angular velocity and stator current. Through computer simulation results of this proposed system, it is shown that the BLSM drive has a ability of precision torque control from the static and dynamic performance.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.156-160
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• 2000

When the structure supporting the rotor as well as the rotor itself is in the resonant range, it cause the vibration problem. Although the static characteristics of structures was considered during the design process, we must consider the resonance problem between the excitation(the main revolution frequency of the rotor) between the dynamic characteristics of its structures. This paper presents we improved the dynamic characteristic of a bearing support system to remove a resonance problem so that stabilized the turbine-generator system.

• Tribology and Lubricants
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• v.37 no.6
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• pp.261-272
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• 2021

This study investigates the structural characteristics of oil-free, gas beam foil journal bearings (GBFJBs) for use in high speed motors. Mathematical modeling was carried out, and reaction force modeling for static load was performed to predict the structural characteristics of the GBFJB. Mathematical modeling and reaction force modeling for static load are performed to predict the structural characteristics of GBFJBs. The reaction force of the test bearing against static loads was measured during experiments and compared with the predicted results. The measured experimental data reveal the nonlinear stiffness characteristics of the GBFJB against varying displacement and agree well with the predictions. Dynamic load tests using an exciter allow to identify the vibration characteristics of the GBFJB. Test results show that the vibration displacement, dynamic force, and acceleration measured on the test bearing are most dominant at the applied dynamic load (synchronization) frequency. Futhermore, the test results show that the hysteresis area recorded during the dynamic tests increases with the excitation amplitude and frequency, and that the beam stick phenomena occurr at high excitation frequencies. The single degree of freedom (DOF) vibration model aids to identify the stiffness and damping coefficient of the GBFJB, which decrease as the excitation frequency increases.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.7
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• pp.627-634
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• 2014

Machine tool vibration is well known for reducing machining accuracy. Because vibration response of a linear structure generally depends on its transfer function if the magnitude of excitation were kept constant, this study introduces a RET(Random Excitation Test) based on FRF method to evaluate stiffness of a prototype HDMTL(Heavy-Duty Multi-Tasking Lathe) for large crankshaft of marine engine. Firstly, two force loops of the lathe and corresponding structural loops were identified:1) workpiece - spindle - head stock - main bed, 2) workpiece - tool post - carriage bed. Secondly, compliances of each structural loop were measured respectively using RET with a hydraulic exciter and then converted into stiffness. Finally, the measured stiffness was compared with that obtained previously by FEM analysis. As the result, both measured and computed stiffness were closely in agreement with each other. And the prototype HDMTL has evidently sufficient rigidity above ordinary heavy-duty lathes.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.993-999
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• 2008

A girder height limitation is the critical parameter for rapid construction of bridge deck and construction space limitation especially in urban area such as high population area and high density habitats. A standard post-tensioned I-shaped concrete girder usually demands relatively higher girder height in order to retain sufficient moment arm between compression force and tensile force. To elaborate this issue, a small U-shaped section with wide flanges can be used as a possible replacement of I-shaped standard girder. This prestressed concrete box girder allows more flexible girder height adjustment rather than standard I-shaped post-tensioned girder plus additional torsion resistance benefits of closed section. A 30m-long, 1.7m-high and 3.63m-wide actual small prestressed concrete box girder is designed and a laboratory test for its static behaviors by applying 6,200kN amount of load in the form of 4-point bending test was performed. The load-deflection curve and crack patterns at different loading stage are recorded. In addition, to extracting the dynamic characteristics such as natural frequency and damping ratio of this girder, several excitation tests with artificial mechanical exciter with un-symmetric mass are carried out using operational frequency sweep-up. Nonlinear finite element analysis of this 4 point bending test under monotonic static load is investigated and discussed with aids of concrete damaged plasticity formulation using ABAQUS program.

• Structural Engineering and Mechanics
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• v.71 no.4
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• pp.391-405
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• 2019

Compared to the ambient vibration test mainly identifying the structural modal parameters, such as frequency, damping and mode shapes, the impact testing, which benefits from measuring both impacting forces and structural responses, has the merit to identify not only the structural modal parameters but also more detailed structural parameters, in particular flexibility. However, in traditional impact tests, an impacting hammer or artificial excitation device is employed, which restricts the efficiency of tests on various bridge structures. To resolve this problem, we propose a new method whereby a moving vehicle is taken as a continuous exciter and develop a corresponding flexibility identification theory, in which the continuous wheel forces induced by the moving vehicle is considered as structural input and the acceleration response of the bridge as the output, thus a structural flexibility matrix can be identified and then structural deflections of the bridge under arbitrary static loads can be predicted. The proposed method is more convenient, time-saving and cost-effective compared with traditional impact tests. However, because the proposed test produces a spatially continuous force while classical impact forces are spatially discrete, a new flexibility identification theory is required, and a novel structural identification method involving with equivalent load distribution, the enhanced Frequency Response Function (eFRFs) construction and modal scaling factor identification is proposed to make use of the continuous excitation force to identify the basic modal parameters as well as the structural flexibility. Laboratory and numerical examples are given, which validate the effectiveness of the proposed method. Furthermore, parametric analysis including road roughness, vehicle speed, vehicle weight, vehicle's stiffness and damping are conducted and the results obtained demonstrate that the developed method has strong robustness except that the relative error increases with the increase of measurement noise.