• Title/Summary/Keyword: Energy stability

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Evaluation of Electrochemical Stability of Graphite Current Collector for Electric Double Layer Capacitor Based on Acid Electrolyte (산성 전해질 기반의 전기 이중층 커패시터용 흑연 집전체의 전기화학적 안정성 평가)

  • Park, Sijin;An, Geon-Hyoung
    • Korean Journal of Materials Research
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    • v.31 no.5
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    • pp.272-277
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    • 2021
  • Owing to its low cost, easy fabrication process, and good ionic properties, aqueous supercapacitors are under strong consideration as next-generation energy storage devices. However, the limitation of the current collector is its poor electrochemical stability, leading to low energy storage performance. Therefore, a reasonable design of the current collector and the acidic electrolyte is a necessary, as well as interfacial engineering to enhance the electrochemical performance. In the present study, graphite foil, with excellent electrochemical stability and good electrical properties, is suggested as a current collector of aqueous supercapacitors. This strategy results in excellent electrochemical performance, including a high specific capacitance of 215 F g-1 at a current density of 0.1 A g-1, a superior high-rate performance (104 F g-1 at a current density of 20.0 A g-1), and a remarkable cycling stability of 98 % at a current density of 10.0 A g-1 after 9,000 cycles. The superior energy storage performance is mainly ascribed to the improved ionic diffusion ability during cycling.

Direct Energy Method of Power System Stability Analysis and its Application by using Energy Conservation Law (에너지보존법칙을 이용한 전력계통 안정도 직접 해석법에서의 응용)

  • Lee, Yong-Hoon;Cho, Byoung-Hoon;Ryu, Heon-Su;Moon, Young-Hyun
    • The Transactions of the Korean Institute of Electrical Engineers A
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    • v.48 no.10
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    • pp.1207-1214
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    • 1999
  • Many papers have recently been presented to develop energy functions for power systems. However, earlier studies adopted case-by-case approaches, which failed to give a general approach to deal with various kinds of generator models. In this paper, two useful theorems are developed regarding the integral relationships of the generator power versus its phasor current and voltage. By using the proposed theorems, an exact energy conservation law can be derived from the complex integral. The proposed energy conservation law, which is free of the generator model, can be utilized to develop energy functions for various kinds of generator models including the speed governors and exciters. An illustrative example is given for a multimachine system with the Eq' model of generator. This thesis also shows a possibility of more accurate and fast stability analysis by using the proposed Energy Conservation Law.

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Energy Conservation Law and its application for Direct Energy method of Power System Stability (에너지 보존법칙과 전력계통 안정도 직접 해석법에서의 응용)

  • Moon, Young-Hyun;Lee, Yong-Hoon;Cho, Byoung-Hoon;Ryu, Heon-Su;Choi, Byoung-Kon
    • Proceedings of the KIEE Conference
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    • 1998.11a
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    • pp.263-268
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    • 1998
  • Many papers have recently been presented to develop energy functions for power systems. However, earlier studies adopted case-by-case approaches, which failed to give a general approach to deal with various kinds of generator models. In this paper, two useful theorems are developed regarding the integral relationships of the generator power versus its phasor current and voltage. By using the proposed theorems, an exact energy conservation law can be derived from the complex integral. The proposed energy conservation law, which is free of the generator model, can be utilized to develop energy functions for various kinds of generator models including the speed governors, and exciters. An illustrative example is given for a multimachine system with the Eq' model of generator. This thesis also shows a possibility of more accurate and fast stability analysis by using the proposed Energy Conservation Law.

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The Annual Averaged Atmospheric Dispersion Factor and Deposition Factor According to Methods of Atmospheric Stability Classification

  • Jeong, Hae Sun;Jeong, Hyo Joon;Kim, Eun Han;Han, Moon Hee;Hwang, Won Tae
    • Journal of Radiation Protection and Research
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    • v.41 no.3
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    • pp.260-267
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    • 2016
  • Background: This study analyzes the differences in the annual averaged atmospheric dispersion factor and ground deposition factor produced using two classification methods of atmospheric stability, which are based on a vertical temperature difference and the standard deviation of horizontal wind direction fluctuation. Materials and Methods: Daedeok and Wolsong nuclear sites were chosen for an assessment, and the meteorological data at 10 m were applied to the evaluation of atmospheric stability. The XOQDOQ software program was used to calculate atmospheric dispersion factors and ground deposition factors. The calculated distances were chosen at 400 m, 800 m, 1,200 m, 1,600 m, 2,400 m, and 3,200 m away from the radioactive material release points. Results and Discussion: All of the atmospheric dispersion factors generated using the atmospheric stability based on the vertical temperature difference were shown to be higher than those from the standard deviation of horizontal wind direction fluctuation. On the other hand, the ground deposition factors were shown to be same regardless of the classification method, as they were based on the graph obtained from empirical data presented in the Nuclear Regulatory Commission's Regulatory Guide 1.111, which is unrelated to the atmospheric stability for the ground level release. Conclusion: These results are based on the meteorological data collected over the course of one year at the specified sites; however, the classification method of atmospheric stability using the vertical temperature difference is expected to be more conservative.

Transient Stability Enhancement of Power System by Using Energy Storage System (에너지저장시스템을 이용한 전력계통의 과도안정도 향상)

  • Seo, Gyu-Seok
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.18 no.12
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    • pp.26-31
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    • 2017
  • The conventional method of improving the transient stability in a power system is the use of reactive power compensation devices, such as the STATCOM and SVC. However, this traditional method cannot prevent the rapid voltage collapse brought about by the stalling of the motor due to a system fault. On the other hand, the ESS (Energy Storage System) provides fast-acting, flexible reactive and active power control. The fast-acting power compensation provided by an energy storage system plays a significant role in enhancing the transient stability after a major fault in the power system. In this paper, a method of enhancing the transient stability using an energy storage system is proposed for power systems including a dynamic load, such as a large motor. The effectiveness of the energy storage system compared to conventional devices in enhancing the transient stability of the power system is presented. The results of the simulations show that the simultaneous injection of active and reactive power can enhance the transient stability more effectively.

Transient Stability Enhancement of Power System by Using Energy Storage System (풍력터빈 발전기가 연계된 전력계통에서 에너지저장시스템이 과도안정도에 미치는 영향)

  • Seo, Gyu-Seok
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.20 no.6
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    • pp.592-597
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    • 2019
  • A conventional method to improve transient stability in power system is the use of reactive power compensation devices such as STATCOM and SVC. However, this traditional method cannot prevent a rapid voltage collapse brought on by motors stalling due to system fault. On the other hand, ESS(Energy Storage System) provides fast-acting, flexible reactive and active power control. The fast active power compensation with energy storage system plays a significant role in transient stability enhancement after a major fault of power system. In this paper, transient stability enhancement method by using energy storage system is proposed for the power system including a dynamic load such as large motor. The effectiveness of energy storage system compared to conventional devices in enhancing transient stability of power system is presented. The results of simulations show that the simultaneous injection of active and reactive power can enhance more effectively transient stability.

Real-time Stability Assessment and Energy Margin Estimation using Fuzzy (퍼지를 이용한 실시간 안정도 판별과 에너지 마진의 추정)

  • Choi, Won-Chan;Kim, Soo-Nam;You, Seok-Ku
    • Proceedings of the KIEE Conference
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    • 1999.07c
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    • pp.1239-1241
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    • 1999
  • In this paper, we propose real time transient stability assessment and energy margin estimation using fuzzy approximate reasoning. The proposed method used rotor angle, kinetic energy and acceleration power of generators at clearing time as fuzzy input. In order to calculate energy margin in transient energy function (TEF), we obtained controlling unstable equilibrium point (UEP) using mode of disturbance procedure (MOD). The proposed algorithm is tested on 4-machine, 6-bus, 7-line power system to prove of effectiveness.

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Transient Stability Analysis of Power System by Transient Energy Method (과도에너지법에 의한 전력계통의 과도안정도 해석에 관한 연구)

  • 김준현;설용태
    • The Transactions of the Korean Institute of Electrical Engineers
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    • v.32 no.2
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    • pp.59-64
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    • 1983
  • This paper deals with the transient energy method of transient stability analysis of multi-machine power system by improving the transfer conductance, the kinetic energy and the critical transient energy. The tranfer conductance is considered more correctly, the generators of system are seperated to two states (critical and the rest state)and the correction term of critical transient energy (to reference point) is added. This analysis is performed by digital computer simulation and the application of this method to two model systems has shown its superiority to other available methods.

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Analysis of Control Stability and Performance of Magnetically-Levitated Flywheel Energy Storage System using Flexible Rotor Model (유연체 회전축 모델을 이용한 자기부상형 플라이휠 에너지 저장장치의 제어시스템 안정성 및 성능 해석)

  • Yoo, Seong-Yeol;Lee, Wook-Ryun;Bae, Yong-Chae;Noh, Myoung-Gyu
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2009.10a
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    • pp.258-263
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    • 2009
  • This paper describes an analysis of the stability and performance of a large-capacity flywheel energy storage system (FESS) supported by active magnetic bearings. We designed and manufactured the system that can store up to 5kWh of usable energy at the maximum speed of 18,000 rpm. In order to analyze the stability of the systems accurately, we derived a rigid body rotor model, flexible rotor model using finite-element method, and a reduced-order model using modal truncation. The rotor model is combined with those of active magnetic bearings, amplifiers, and position sensors, resulting in a system simulation model. This simulation model is validated against experimental measurements. The stability of the system is checked from the pole locations of the closed-loop transfer functions. We also investigated the sensitivity function to quantify the robustness of the systems to the disturbances such as mass imbalance and sensor noises.

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Mesh Stability Study for the Performance Assessment of a Deep Geological Repository Using APro

  • Hyun Ho Cho;Hong Jang;Dong Hyuk Lee;Jung-Woo Kim
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.21 no.2
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    • pp.283-294
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    • 2023
  • APro, developed in KAERI for the process-based total system performance assessment (TSPA) of deep geological disposal systems, performs finite element method (FEM)-based multiphysics analysis. In the FEM-based analysis, the mesh element quality influences the numerical solution accuracy, memory requirement, and computation time. Therefore, an appropriate mesh structure should be constructed before the mesh stability analysis to achieve an accurate and efficient process-based TSPA. A generic reference case of DECOVALEX-2023 Task F, which has been proposed for simulating stationary groundwater flow and time-dependent conservative transport of two tracers, was used in this study for mesh stability analysis. The relative differences in tracer concentration varying mesh structures were determined by comparing with the results for the finest mesh structure. For calculation efficiency, the memory requirements and computation time were compared. Based on the mesh stability analysis, an approach based on adaptive mesh refinement was developed to resolve the error in the early stage of the simulation time-period. It was observed that the relative difference in the tracer concentration significantly decreased with high calculation efficiency.