• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.401-407
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• 2004

This study is on the constant-current stress corrosion test related to the load stress in welded zone and non-welded zone of high tensile strength steel for natural gas transmission. The surface corrosion pattern of the welded zone of API 5L-X65 specimens for natural gas transmission showed global corrosion and narrow pitting, and the pitting was increased by increasing the load stress. Initially, the average relative electrode potential and the average relative current of the high tensile strength steel for natural gas transmission specimens was decreased suddenly, and the average relative electrode potential was higher and the average relative current was lower in welded zone than base metal. and the average relative electrode potential was decreased by increasing the load stress, and the average relative current was somewhat increased by increasing the load stress. The corrosion rate was less in welded zone than base metal, and the corrosion rate was decreased by increasing the load stress.

• Proceedings of the KIPE Conference
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• 2006.06a
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• pp.492-494
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• 2006

Neutral line current is analyzed by the neutral line CF in nonlinear load balanced and unbalanced conditions. The worst nonlinear load condition is nonlinear balanced load condition, and It is below CFNL=1.194 that a neutral line current could not excess the rated value

• Journal of Power Electronics
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• v.17 no.2
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• pp.551-560
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• 2017

The present study proposes an angle droop controller for converter interfaced (dispatchable) distributed generation (DG) resources in the islanded mode of operation. Due to the necessity of proper real and reactive power sharing between different types of resources in microgrids and the ability of systems to respond properly to abnormal conditions (sudden load changes, load uncertainty, load current disturbances, transient conditions, etc.), it is necessary to produce appropriate references for all of the mentioned above conditions. The proposed control strategy utilizes a current controller in addition to an angle droop controller in the discrete time domain to generate appropriate responses under transient conditions. Furthermore, to reduce the harmonics caused by switching at converters' output, a LCL filter is used. In addition, a comparison is done on the effects that LCL filters and L filters have on the performance of DG units. The performance of the proposed control strategy is demonstrated for multi islanded grids with various types of loads and conditions through simulation studies in the DigSilent Power Factory software environment.

• Journal of Power Electronics
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• v.18 no.1
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• pp.300-308
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• 2018

An online estimation method for wireless power transfer (WPT) systems is presented without using any measurement of the secondary side or the load. This parameter estimation method can be applied with a controlling strategy that removes both the receiving terminal controller and the wireless communication. This improves the reliability of the system while reducing its costs and size. In a wireless power transfer system with an LCCL impedance matching circuit under a rectifier load, the actual load value, voltage/current and mutual inductance can be reflected through reflected impedance measuring at the primary side. The proposed method can calculate the phase angle tangent value of the secondary loop circuit impedance via the reflected impedance, which is unrelated to the mutual inductance. Then the load value can be determined based on the relationships between the load value and the secondary loop impedance. After that, the mutual inductance and transfer efficiency can be computed. According to the primary side voltage and current, the load voltage and current can also be detected in real-time. Experiments have verified that high estimation accuracy can be achieved with the proposed method. A single-controller based on the proposed parameter estimation method is established to achieve constant current control over a WPT system.

• Journal of IKEEE
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• v.26 no.3
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• pp.462-467
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• 2022

The feedback buffer structure is proposed to alleviate the overshoot and undershoot phenomenon and the regulation of the output voltage. The conventional LDO regulator undergoes a regulation voltage change caused by a constant load current change. An LDO regulator with a feedback voltage sensing structure operates in the input voltage range of 3.3 to 4.5 V and has a load current of up to 150 mA at output voltage of 3 V. According to the simulation results, a regulation value of 6.2 mV was ensured when the load current uniformly changed to 150 mA.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.7
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• pp.363-368
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• 1999

The parallel operation system of multiple uninterruptible power supplies(UPSs) is used to increase power capacity of the system or to secure higher reliability at critical loads. In the parallel operation of the two UPSs, the load-sharing control to maintain the current balance between them is a key technique. Because a UPS has low output impedance and quick response characteristics, in case of an unbalanced load inverter output current changes very rapidly and thereby can instantaneously reach an overload condition. In this study, high precise load-sharing controller is proposed and implemented for the parallel operation system of two UPSs with low impedance characteristics and this controller controls the frequency and the voltage to minimize the active power component and the reactive power component which are gotten from the current difference between two UPSs. And then a good performance of the proposed method is verified by experiments in the parallel operation system with two 40KVA UPSs.

• Progress in Superconductivity and Cryogenics
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• v.6 no.1
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• pp.43-48
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• 2004

This paper deals with design and fabrication of heater-triggered switching system for the high-Tc superconducting (HTS) power supply with series-connected double-pancake load. Amongst all components, heater triggering is the most important element for the performance of HTS power supply. To fabricate the optimal heater-triggered system, its characteristics have been analysed through the simulation and expriment. The thermal analysis of switching parts of the Bi-2223 solenoid according to the heater input was carried out. Based upon the analysis, 8A electromagnet current and 1.5A DC Heater current were optimally derived, and 8s and 20s for the pumping period were selected in this experiment. In the experiment. the maximum pumping current reached about 24A with Bi-2223 pancake load of 6mH.

• International Journal of Ocean System Engineering
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• v.3 no.4
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• pp.164-168
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• 2013

Tidal-current power is now recognized as a clean power resource. The turbine blade is the fundamental component of a tidal current power turbine. The kinetic energy available within a tidal current can be converted into rotational power by turbine blades. While in service, turbine blades are generally subjected to cyclic fatigue loading due to their rotation and the rotor-tower interaction. Predicting the fatigue life under a hydrodynamic fatigue load is very important to prevent blade failure while in service. To predict the fatigue life, hydrodynamic load data should be acquired. In this study, the vibration characteristics were analyzed based on three-dimensional unsteady simulations to obtain the cyclic fatigue load. Our results can be applied to the fatigue design of horizontal-axis tidal turbines.

• Proceedings of the KIEE Conference
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• summer
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• pp.1370-1372
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• 2004

At present. distance relay and ${\Delta}I$ current increment relay are used as primary and secondary protection in the AC feeder system. However. electric railway vehicles according to power electronic's development had developed resistance control, thyristor phase control and PWM control system. and operation of train is increasing in a feeder section. Therefore this paper analyzes the load characteristics and situation of relay's maloperation caused by load current increase, harmonics, regenerative braking current and operation of the different vehicles in same feeder section. Based on this analysis. this paper proposes consideration items for relay correction and advanced adaptive relay that can change operation area according to load current.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.65 no.3
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• pp.210-215
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• 2016

The transient characteristics of the Mg/Air fuel cell were ascribed to the load current, electrolyte concentrations, air electrode area and electrode distance. It was found that transient phenomena occurred in the load current, which is due to activate of the oxidation and reduction reaction process. The transient time increase with the load current increase. The transient characteristics were investigated with regard to internal resistance. The maximum power output analysis was employed in order to explain the delayed action under various experimental conditions. The internal resistances had a significant effect on the transient characteristics. The transient curves thus obtained were in almost agreement with internal resistance characteristics.