• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.4
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• pp.428-432
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• 2014

Rotating machines are an integral part of large electrical power machinery in most of the industries. Any degradation or outages in the rotating electric machinery can result in significant losses in productivity. It is critical to monitor the equipment for any degradation's so that it can serve as an early warning for adequate maintenance activities and repair. Prior research and field studies have indicated that the rotating machines have a particular type of signal structure during the initial start-up transient. A machine performance can be studied based on the effect of degradation in signal parameters. In this paper a data-acquisition system and the FFT algorithm has been design and model using the MATLAB and Simulink. The implementation had been carried out on the TMS320 DSP Processor and various testing and verification of the machine performance had been carried out. The results show good agreement with expected results for both simulated and real-time data. The real-time data from AC water pumps which have rotating motors built-in were collected and analysed. The FFT algorithm provides frequency response and based on this frequency response performance of the machine had been measured.The FFT algorithm provides only approximation about the machine performances.

• Progress in Superconductivity and Cryogenics
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• v.22 no.3
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• pp.13-19
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• 2020

This study presents the experiment and simulation results on the magnetic field response and electrical stability behaviors of no-insulation (NI) and metal insulation with stainless steel tape (MI-SS) which wound in form of racetrack type coils. First of all, the structural design of the racetrack type bobbin was shown along with its parameters. Then, the current-voltage tests were carried out to measure the critical current of both test coils. Also, the sudden discharging and charging tests were performed in the steady state to estimate the decay field time and magnetic field response, respectively. Finally, the overcurrent tests were conducted in the transient state to investigate the electrical stability of these test coils. Based on the experimental results, the contact surface resistances were calculated and applied to the field coils (FCs) of 10-MW-class second generation high temperature superconducting generator (2G HTSG) used in wind offshore environment. The charging delay time and electrical stability for NI and MI-SS HTS FCs of 10-MW-class 2G HTSG are analyzed by the equivalent circuit model and the key parameters which were obtained from the electromagnetic finite element analysis results.

• Journal of computational fluids engineering
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• v.6 no.2
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• pp.22-31
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• 2001

The two-dimensional unsteady incompressible viscous flow behind rectangular bluff bodies between two parallel plates was analyzed numerically. The steady state flow and the vortex flow behind rectangular bluff bodies in the channel were investigated for two regimes i.e., the laminar(Re = 100, 300, 500) and the turbulent flows(Re = 10⁴∼10/sup 6/). The vortex shedding was generated by a physical disturbance(6%) numerically imposed at the rear of the bluff bodies for a short time. It was observed that the perturbed flow became periodic after a transient period. And in the case of unsteady inflow, the sinusoidal pulsatile flow was applied as the inlet condition in the turbulent flow of Reynolds number of 1.0×10/sup 5/. FLUENT code was employed to solve the problems. The power-law scheme was used to get stable linearized equations and the PISO algorithm was applied to finding the solution of them.

• New & Renewable Energy
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• v.3 no.4
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• pp.8-15
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• 2007

Liquid water in flow channel is an important factor that limits the steady and transient performance of PEM fuel cells. A computational fluid dynamics study based on the volume-of-fluid [VOF] multi-phase model was conducted to understand the two-phase flow behavior of liquid water in cathode gas channels. The liquid water transport in $180^{\circ}{\Delta}$ bends was investigated, where the effects of surface characteristics (hydrophilic and hydrophobic surfaces], channel geometries (rectangular and chamfered corners], and air velocity in channel were discussed. The two-phase flow behavior of liquid water with hydrophilic channel surface and that with hydrophobic surface was found very different; liquid water preferentially flows along the corners of flow channel in hydrophilic channels while it flows in rather spherical shape in hydrophobic channels. The results showed that liquid water transport was generally enhanced when hydrophobic channel with rounded corners was used. However, the surface characteristics and channel geometries became less important when air velocity was increased over 10m/s. This study is believed to provide a useful guideline for design optimization of flow patterns or channel configurations of PEM fuel cells.

• Journal of Ocean Engineering and Technology
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• v.28 no.6
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• pp.508-516
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• 2014

A numerical method to investigate the non-linear motion characteristics of a TLP is established. A time domain simulation that includes the memory effect using the convolution integral is used to consider the transient effect of TLP motion. The hydrodynamic coefficients and wave force are calculated using a potential flow model based on the HOBEM(higher order boundary element method). The viscous drag force acting on the platform and tendons is also considered by using Morison’s drag. The results of the present numerical method are compared with experimental data. The focus is the nonlinear effect due to the viscous drag force on the TLP motion. The ringing, springing, and drift motion are due to the drag force based on Morison's formula.

• Journal of the Korean Society of Safety
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• v.29 no.6
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• pp.104-110
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• 2014

The Han River is the only waterway in Korea where estuary is not blocked by dykes so that tidal water is flowing in and out through the tidal reach. The extreme tidal range in the Yellow Sea causes an intense flood current, stretching over horizontal extents of tens of kilometers into the rivers. To elucidate the flow reversal by discharge conditions and transient tidal level in the Han river, numerical simulations were conducted under 7 boundary conditions for two days with 10 minute time step. As the flow conditions changed from low discharge and high tidal difference to high discharge and low tidal difference, the flow reversals became weaker and the velocity of forward flow direction became higher due to the increased flow momentums and decreased tidal differences. In the case of normal flow, the maximum reverse velocity was 0.4 m/s, which was equivalent to the maximum forward velocity. In addition, the pattern of the development and decay of forward and reverse flow was presented.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.9
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• pp.59-64
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• 2015

IEC is an international standards which are used in many countries with Europe as the center. IEC standard is introduced in Korea according to WTO/TBT agreements, however until now there are no buildings in Korea which are designed applying IEC standard. Therefore, KEA(Korea Electric Association) is scheduled to construct Korean low voltage electrical installation integration test site which is designed applying IEC standard. In this paper, before being under construction of Korean low voltage electrical installation integration test site, power substation is modeled based on real design parameters and method to select circuit breakers and cables is presented applying IEC standard in the modeled power substation. EMTP(ElctroMagnetic Transient Program) is used for simulation program. EMTP which is power system analysis program is easy to model power system and power substation.

• Journal of Power Electronics
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• v.18 no.4
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• pp.1111-1126
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• 2018

In modern power systems, distributed generators (DGs) result in high stress on system frequency stability. Apart from the intermittent nature of DGs, most DGs do not contribute inertia or damping to systems. As a result, a new control method referred to as a virtual synchronous machine (VSM) has been proposed, which brought new characteristics to inverters such as synchronous machines (SM). DGs employing an energy storage system (ESS) provide inertia and damping through VSM control. Meanwhile, energy storage presents some physical constraints in the VSM implementation level. In this paper, a VSM mathematical model is built and analyzed. The dynamic responses of the output active power are presented when a step change in the frequency occurs. The influences of the inertia constant, damping factor and operating point on the ESS volume margins are investigated. In addition, physical constraints are proposed based on these analyses. The proposed physical constraints are simulated using PSCAD/EMTDC software and tested through RTDS experiment. Both simulation and RTDS test results verify the analysis.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.2152_2153
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• 2009

In this study, the dynamic characteristic of a contact wire and pantograph suppling electrical power to high-speed trains are investigated from an electrical response point of view. To analysis power line disturbance by induced contact loss phenomenon for high speed operation, a hardware Simulator which considered contact loss between contact wire and the pantograph as well as contact wire deviation is developed. It is confirmed that a contact wire and pantograph model are necessary for studying the dynamic behavior of the pantograph system. One of the most important needs accompanied by increasing the speed of high-speed train is reduced that an arc phenomenon by loss of contact brings out EMI. In case of a high-speed train using electrical power, as comparison with diesel rolling stock, PLD(Power Line Disturbance) such as harmonic, transient voltage and current, EMI, dummy signal injection etc usually occurs. Throughout experiment, it is verified that an arc phenomenon is brought out for simulator operation and consequently conducted noise is flowed in electric circuit by power line disturbance.

• Journal of Electrical Engineering and Technology
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• v.12 no.4
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• pp.1495-1502
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• 2017

The Theory of operation of switched reluctance motors (SRM) depends on the reluctance torque, where energy is transferred to stator winding only. Although its construction is simple, the electrical design is complex, due to the switching configuration needed to deliver power to stator coils. However, because of the nonlinearly of magnetic circuit, SRM has torque ripple. This paper proposes a new strategy to drive SRM from a single-phase AC supply. Each stator winding is connected to AC-DC or AC-AC converters, which is called branch. All branches are connected in parallel to a single-phase AC supply. A shaft encoder allows current production in stator winding during the positive torque production region and terminates it during the negative torque production region. A magnetic flux is produced between stator poles when current is supplied from AC supply to stator coil and repeats many cycles as long as the rate of change of stator inductance is positive. Different possibilities for the configurations of AC-AC or AC-DC converters are introduced to drive SRM from the single-phase AC supply. A case study is presented for a SRM fed from AC supply through semi-controlled AC-DC converter is presented. A simulation model is introduced and verified by experimental rig for two-phase SRM.