Gi-Hyeon Gwon

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 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).

Short-Circuit Fault Protection of a Low Voltage DC Distribution System using Superimposed Current Components

Low voltage DC (LVDC) distribution systems are gaining attention as customer loads are shifting towards power electronics-based equipment. The DC distribution system has the advantage of supplying power to these power electronic-based loads with high efficiency and without undergoing an energy conversion process. However, the power electronic components used in the LVDC distribution system are vulnerable during short-circuit faults. These components must be protected during the short-circuit faults for a safe and reliable operation. Therefore, this paper proposes a protection technique based on DC short-circuit fault current behavior. The fault is detected via a superposition principle. A fault current limiter (FCL) is used to suppress DC fault strength and reduce the stress from the circuit breaker. Finally, a solid state circuit breaker (SSCB) is used to isolate the fault point. The simulation results show that the proposed protection Scheme operates quickly enough as per expectations to avoid damage to sensitive power electronic devices.

A Study on Transient Characteristics in Low Voltage DC Distribution System resulted from the Operation of Protective Device in AC Side

In recent, DC-based power system is being paid attention as the solution for improving the energy efficiency as distributed generations based on renewable energy and digital devices increase. The interest is gradually extended to Low Voltage DC (LVDC) distribution system. To establish the standards for LVDC distribution system, the studies on various aspects based on the comparative analysis between AC system and DC system have conducted. Protection schemes for LVDC distribution system are also included, but most researches have focused on transient characteristics under DC faults so far. This paper, therefore, analyzes the transient characteristics in LVDC distribution system resulted from the operation of protective device by AC fault. Furthermore, it is proposed the considerations to construct the reliable protection schemes. For this purpose, theoretical analysis with the equivalent circuits of LVDC distribution system is performed, and then the analysis results are verified through simulations with ElectroMagnetic Transients Program.

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 (...

A Study on Applicability of Protection Algorithms of AC Distribution System to DC Distribution System

Low Voltage DC (LVDC) distribution system has paid attention because people are trying to improve energy efficiency and reduce loss of energy. In addition, many researches related to DC system are conducted to replace the AC-based power supply due to the increase of digital load and distributed generation. However, research on standard and protection scheme is still incomplete to achieve the stable and reliable operation of LVDC distribution system. Thus this paper studies protection algorithms in the LVDC distribution system. First, this paper analyzes proper protection algorithms in LVDC distribution system by comparing with those in AC distribution system. And then, it performs the modelling of a simple LVDC distribution system and the simulation by using EMTP(ElectroMagnetic Transients Program).

Detection of high-impedance fault in low-voltage DC distribution system via mathematical morphology

This study presents a method for high-impedance fault (HIF) detection in a low-voltage DC (LVDC) distribution system via mathematical morphology (MM), which is composed of two elementary transforma...

A Novel Method for Deriving Optimal Synchronism-Check Phase Angle in Transmission System

Most of faults occurring in transmission system are transient. To cope with such faults, automatic reclosing is applied and it is economic and effective method to improve the reliability and transient stability of power system. Many countries applying 3-phase and leader-follower reclosing scheme use a synchronism-check relay to limit impacts associated with automatic reclosing under Live-Bus/Live-Line (LBLL) conditions. Most utilities generally use a standardized conservative setting that is in the range of 20° to 30°. However, it might be sometimes not a good idea because each transmission line in system has different system conditions such as system structure, line length and load flow that might result in undesirable system impacts. Therefore, it is necessary to derive the Optimal Synchronism-Check (OSC) phase angle which is appropriate for each transmission system. In this paper, a novel method composed of three steps is proposed to derive the OSC phase angle. The proposed method is applied to transmission system based on actual data from Korea. Computer simulations are performed using ElectroMagnetic Transient Program (EMTP) and simulation results show that proposed method is valid and effective.

A Reliability Analysis in LVDC Distribution System Considering Power Quality

Recently, DC-based power system is being paid attention as the solution for energy efficiency. As the example, HVDC (High Voltage DC) transmission system is utilized in the real power system. On the other hand, researches on LVDC (Low Voltage DC) distribution system, which are including digital loads, are not enough. In this paper, reliability in LVDC distribution system is analyzed according to the specific characteristics such as the arrangement of DC/DC converters and the number of poles. Furthermore, power quality is also taken account of since LVDC distribution system includes multiple sensitive loads and electric power converters. In order to achieve this, LVDC distribution systems are modeled using ElectroMagnetic Transient Program (EMTP) and both the minimal cut-set method and Customer Interruption Cost (CIC) are used in the reliability analysis.