Yun-Sik Oh

An Adaptive Autoreclosure Scheme with Reference to Transient Stability for Transmission Lines

Autoreclosure provides a means of improving power transmitting ability and system stability. Conventional reclosure adopts the fixed dead time interval strategy, where the reclosure is activated after a time delay to restore the system to normal as quickly as possible without regard to the system conditions. However, these simple techniques cannot provide optimal operating performance. This paper presents an adaptive autoreclosure algorithm including variable dead time, optimal reclosure, phase-by-phase reclosure and emergency extended equal-area criterion (EEEAC) algorithm in order to improve system stability. The reclosure algorithm performs the operations that are attuned to the power system conditions. The proposed adaptive reclosure algorithm is verified and tested using ATP/EMTP MODELS, and the simulation results show that the system oscillations are reduced and the transient stability is enhanced by employing the proposed adaptive reclosure algorithm.

Algorithm for Fault Detection and Classification Using Wavelet Singular Value Decomposition for Wide-Area Protection

An algorithm for fault detection and classification method for wide-area protection in Korean transmission systems is proposed. The modeling of 345-kV and 765-kV Korean power system transmission networks using the Electro Magnetic Transient Program - Restructured Version (EMTP- RV) is presented and the algorithm for fault detection and classification in transmission lines is developed. The proposed algorithm uses the Wavelet Transform (WT) and Singular Value Decomposition (SVD). The Singular value of Approximation coefficient (SA) and part Sum of Detail coefficient (SD) are introduced. The characteristics of the SA and SD at the fault conditions are analyzed and used in the algorithm for fault detection and classification. The validation of the proposed algorithm is verified by various simulation results.

Development of Fault Detector for Series Arc Fault in Low Voltage DC Distribution System using Wavelet Singular Value Decomposition and State Diagram

It is well known that series arc faults in Low Voltage DC (LVDC) distribution system occur at unintended points of discontinuity within an electrical circuit. These faults can make circuit breakers not respond timely due to low fault current. It, therefore, is needed to detect the series fault for protecting circuits from electrical fires. This paper proposes a novel scheme to detect the series arc fault using Wavelet Singular Value Decomposition (WSVD) and state diagram. In this paper, the fault detector developed is designed by using three criterion factors based on the RMS value of Singular value of Approximation (SA), Sum of the absolute value of Detail (SD), and state diagram. LVDC distribution system including AC/DC and DC/DC converter is modeled to verify the proposed scheme using ElectroMagnetic Transient Program (EMTP) software. EMTP/MODELS is also utilized to implement the series arc model and WSVD. Simulation results according to various conditions clearly show the effectiveness of the proposed scheme.

Development of a Reclosing Scheme for Reduction of Turbine Generator Shaft Torsional Torques: A Decision Method to Achieve Optimal Reactor Capacity

It is well known that line switching operations like reclosing are able to cause transient power oscillations which can stress or damage turbine generators. This paper presents a reclosing scheme to reduce the shaft torsional torques of turbine generators by inserting an additional reactor. A novel method to determine optimal reactor capacity to minimize the torsional torque generated in a turbine generator is also proposed. In this paper, the turbine generator shaft is represented by a multi- mass model to measure torsional torques generated in the shaft between the turbine and the generator. Transmission systems based on actual data from Korea are modeled to verify the proposed scheme using ElectroMagnetic Transient Program (EMTP) software. The simulation results clearly show the effectiveness of the proposed scheme and torsional torque can be minimized by applying the proposed scheme.

Development of an Algorithm for Detecting High Impedance Fault in Low Voltage DC Distribution System using Accumulated Energy of Fault Current

Recently, new Low Voltage DC (LVDC) power distribution systems have been constantly researched as uses of DC in end-user equipment are increased. As in conventional AC distribution system, High Impedance Fault (HIF) which may cause a failure of protective relay can occur in LVDC distribution system as well. It, however, is hard to be detected since change in magnitude of current due to the fault is too small to detect the fault by the protective relay using overcurrent element. In order to solve the problem, this paper presents an algorithm for detecting HIF using accumulated energy in LVDC distribution system. Wavelet Singular Value Decomposition (WSVD) is used to extract abnormal high frequency components from fault current and accumulated energy of high frequency components is considered as the element to detect the fault. LVDC distribution system including AC/DC and DC/DC converter is modeled to verify the proposed algorithm using ElectroMagnetic Transient Program (EMTP) software. Simulation results considering various conditions show that the proposed algorithm can be utilized to effectively detect HIF.

Analysis of Human Safety and System Effect according to Grounding Scheme in LVDC Distribution System

Recent developments and trends in the electric power consumption clearly indicate an increasing use of DC in end-user equipment. According to the trends, new DC power distribution systems have been researched and developed although we presently enjoy a predominantly AC power distribution system. We can use various grounding schemes in DC distribution system as well as in AC distribution system to protect human body and equipments. However, we need to evaluate carefully which grounding scheme is appropriate for a specific system before applying those schemes. In this paper, we analyze the human safety and system effect according to various grounding schemes in Low Voltage DC (LVDC) distribution system. Some components in LVDC distribution system are modeled and computer simulations are conducted by using ElectroMagnetic Transient Program (EMTP).

Analysis of Secondary Arc Extinction Effects according to the Application of Shunt Reactor and High Speed Grounding Switches in Transmission Systems

When secondary arc is caused by single phase tripping, arc should be extinguished prior to high speed reclosing which can make the system restore. In this paper, we analyzes secondary arc extinction by applying two methods that are shunt reactor and High Speed Grounding Switches (HSGS). To verify the effects of these methods in arc extinction aspects, two factors are discussed. One is secondary arc extinction time, and another is recovery voltage. Especially, secondary arc waveform and amplitude value are analyzed to identify the effects of arc extinction methods. Simulation is conducted by using ElectroMagnetic Transient Program (EMTP) based on actual Korea 765kV transmission system.

Protection Coordination Using Superconducting Fault Current Limiters in Microgrids

Power generating units in the form of distributed generation (DG) are integrating with microgrid (MG) systems to supply reliable power to users. The trend of an integrated power supply is increasing continually to meet growing energy demands. Besides certain advantages of the MG system, some interconnection and system protection issues pose a challenge in terms of implementation. These problems need to be addressed in order to facilitate smooth operation of power systems. Superconducting fault current limiters (SFCLs) provide the best performance and unique protection features to electrical power systems during various fault conditions. This paper describes modeling, characterization, and implementation of SFCL in an MG system to enhance protection coordination. The proposed SFCL is modeled in MATLAB/ Simulink software and the performance of the system is validated through simulation results. It is also shown that the proposed SFCL provides a means of better relay coordination during various fault conditions. This is achieved by incorporating well-calculated design parameters of SFCL and its placement at optimal locations.

Analysis of peak shaving effect of demand power using Vehicle to Grid system in distribution system

AbstractIn general, most vehicles are parked during the peak load time so that if we could control these Electric Vehicles suitably and provide the stored electricity from vehicle (battery) to grid, electrical peak load would be reduced. Above function is called as a Vehicle to Grid (V2G). In this paper, we propose the peak load shaving scheme to reduce the peak demand and analyze the effect of V2G system for the peak load shaving in the actual distribution system considering various penetration level of EVs. With the proposed method, peak demand power is reduced considerably.

A study on applicability of Prony’s method to the analysis of the fault characteristics in low voltage DC distribution system

AbstractAs an area of interest in energy efficiency in power systems, low voltage DC (LVDC) distribution system has elicited attention as a potential solution. This system is closely associated with the increase of distributed generations, as well as digital loads. Until now, however, the related standards and research remain insufficient to commercialize the LVDC distribution system. In particular, the establishment of the protection schemes for LVDC distribution systems is the primary task because it can affect the overall aspects, including reliability of the system. For the establishment of reliable protection schemes, the fault characteristics of LVDC distribution system must be identified precisely in a practical system. Thus, this paper shows that Prony’s method can be used to analyze the fault characteristics of LVDC distribution system. For this purpose, the fault characteristics are theoretically analyzed first. The analysis results are then verified by using ElectroMagnetic Transients Program (...