Myong-Chul Shin

Fuzzy logic-based relaying for large power transformer protection

Power transformer protective relay should block the tripping during magnetizing inrush and rapidly operate the tripping during internal faults. The frequency environment of power system has been made more complicated and the quantity of 2nd frequency component in inrush state has been decreased because of the improvement of core steel. Then, traditional approaches will likely be maloperated in the case of magnetizing inrush with low second harmonic component and internal faults with high second harmonic component. This paper proposes a new relaying algorithm to enhance the fault detection sensitivities of conventional techniques by using a fuzzy logic approach. The proposed fuzzy-based relaying algorithm consists of flux-differential current derivative curve, harmonic restraint, and percentage differential characteristic curve. The proposed relaying was tested with relaying signals obtained from Salford EMTP simulation package and showed a fast and accurate trip operation.

Extended integral control for load frequency control with the consideration of generation-rate constraints

This paper presents an extended integral control to load frequency control (LFC) scheme with the presence of generation rate constraints (GRC) in order to get rid of overshoot of the conventional proportional-integral (PI) control. The conventional LFC scheme does not yield adequate control performance with the consideration of the singularities of speed-governor such as rate limits on valve position and GRC. In order to overcome this drawback, an extended integral control is developed for the PI control of the speed governor in the presence of GRC. The key idea of the extended integral control is using a decaying factor to reduce the effects of the error in the past. The decaying factor greatly affects the control performance, and should be carefully selected. This study determines the decaying factor in proportion to the degree of deviation in several levels. The computer simulation has been conducted for the single machine system with various load changes. The simulation results show that the proposed controller based on extended integral control yields much improved control performance, compared to the conventional PI controller.

A Study on Fault Location Estimation Technique Using the distribution Ratio of Catenary Current in AC Feeding System

In AC feeding system, the fault location is calculated by using ratio of current absorbed in the neutral point of AT(Automatic Transformer) or by measuring reactance. In this way, however, an estimation error can be happened due to the many reasons. In addition, for measuring currents in the neutral point of AT, other measuring devices and communication equipments are additionally required. In order to solve the disadvantages, this paper suggests a novel technique using the distribution ratio of catenary current. The proposed technique uses existing protective relays and measures catenary current. With the measured data, we can calculate the distribution ratio of catenary current and determine fault location. Through the simulated results, we derived the correlation between current ratio and fault location. Using this technique, additional equipments and expenses can be reduced. Besides, fault location can be determined more correctly.

Protection profile for software development site

A PP defines an implementation-independent set of IT security requirements for a category of TOEs. Consumers can therefore construct or cite a PP to express their IT security needs without reference to any specific TOE. Generally, PPs contain security assurance requirements about the security of development environment for IT product or system and they are described in ALC_DVS (Development Security) family in the part 3 of the Common Criteria (CC). This paper proposes some security environments for development site by analyzing the compliance between ALC_DVS.1 of the CC and Base Practices (BPs) of the Systems Security Engineering Capability Maturity.

Study of data acquisition and communication equipment for micro-grid system

Recently power systems reduce the use of the fossil fuel and use environment friendly resources. Specially, power systems have more Distributed Generation, which installs near the consumer, increasingly. The resources of Distributed Generation are more clean and economical than conventional generation and fit into the variable power demand. Generally, Distributed Generator installs in consumer or near consumer for reducing transmission cost. The large-scale Distributed Generators connect with Power Company, and supplies electrical power energy to consumer via power grid. On the contrary, small-scale renewable energy resources in consumer side can supply the electrical power to the local consumer and other consumers, which connect with power system. The change of the power system configuration needs for development of the equipment that controls and/or monitoring the power system. There are too many efforts in development of the monitor and control the power system. From these results lead to develop the EMS (Energy Management System) and SCADA (Supervisory Control And Data Acquisition) system. Nevertheless, these systems are too huge and too expensive to install in consumer side that works with small-scale renewable energy source. From that reason, it is need that develop a small size and inexpensive equipment that role of EMS or SCADA. In this paper describes development process of the inexpensive monitoring equipment that works with Distributed Generator at consumer side, and shows validity of measuring data. The roles of developed equipment is measuring voltage/current and storing measured data into hard disk drives in the general PC via USB communication. Further, that is calculating active/reactive power and detecting abnormal conditions and communicates with a higher control system.

A multi-functional platform for implementing intelligent and ubiquitous functions of smart substations under SCADA

For more efficient and economical management of substations under SCADA (Supervisory Control and Data Acquisition) systems, the concept of a smart substation has been introduced using intelligent and ubiquitous IT (Information Technology) techniques. A multi-functional platform needs to perform more intelligent and ubiquitous functions of smart substation effectively. In this paper, we propose a multi-functional platform to implement smart substations effectively. A prototype hardware, functions and communication interfaces on an embedded platform are introduced. Also, we suggest operating system architecture for smart substations.

Research for data acquisition equipment with Micro-Grid system

Micro-grid system, which is connected with power system, should not affect on power quality. Therefore, micro-grid system needs to control system to minimize effect of power quality. In this paper represents the measurement equipment for voltage/current of micro-grid system and the result. This system monitors the state of micro-grid system, such as steady state, islanding operation and reconnection with conventional power system. The equipment has real-time measure function and communication with PC via USB port. This equipment can use various purposes such as investigation of transient state, monitoring of real-time operation and evaluate the power system quality.

A study on an ASIC design technique for digital protective relays

This research presents core-based VLSI design for digital protective relays based on the generalized CORDIC processor. It has high-speed processing capability which is fully sufficient for parallel 12-channel sources at high sampling rate (256 samples per cycle). Required hardware can be quite reasonable in most ASIC technologies. Relaying accuracy is remarkably guaranteed through hardware exponentiation. It also provides re-programmability as in typical instruction set architectures for appropriate parameterization. The entire design was successfully built by 0.35 /spl mu/m CMOS technology with a the size of 5mm /spl times/ 5mm.

Adaptive modulation based power line communication system

In this paper, we present an adaptive modulation/demodulation methods based on each load fluctuation after measuring and modeling of noise pattern due to the various load fluctuations of PLC (power line communication) transmission channel. Additionally, we proposed adaptive modulation for PLC using Decision Making Algorithm that could select the optimum modulation/demodulation methods adaptively according to the various load fluctuation. And we certified the availability of adaptive modulation for PLC using the computer simulation and hardware implementation. The newly proposed adaptive modulation can be widely used to attain the high performance PLC implementation in the severe noise environment due to the load fluctuations.

Generator fault detection technique using detailed coefficients ratio by daubechies wavelet transform

An AC (alternating current) generator is one of the important components in producing a electric power and so it requires highly reliable protection relays to minimize the possiblity of demage occurring under fault conditions. Conventionally, a RDR (ratio differential relaying) based on DFT (discrete Fourier transform) has been used for protecting the stator winding of a generator. However, when DFTs based on Fourier analysis are used, it has been pointed out that defects can occur during the process of transforming a time domain signal into a frequency domain one which can lead to loss of time domain information. This paper proposes the adoption of a protection algorithm for the stator by applying a WT (wavelet transform) to overcome the defects in the DFT process. Moreover, a new ratio equation is proposed for easy utilization of the detailed coefficients by DWT (Daubechies wavelet transform) through the course of MLD (multi-level decomposition) using MATLAB. For the case studies reported in the paper, a model system was established for the simulations utilizing the ATP (alternative transient program), and this verified the effectiveness of the proposed technique through various off-line tests carried out on the collected data. The propose method is shown to be able to rapidly identify internal faults and did not operate a miss-operation for all the external faults tested.