Il-Keun Song

Operation Schemes of Smart Distribution Networks With Distributed Energy Resources for Loss Reduction and Service Restoration

The integration of Distributed Energy Resources (DERs) into the future Smart Distribution Network (SDN) has challenging issues regarding the successful development of smart grids. The SDN offers new opportunities in the improvement of the efficiency of power distribution networks. The DERs will be distributed in the existing distribution networks, interconnected in customer areas and operated on its own schedule without communication to the control center of the existing distribution system. The DER units have both positive and negative effects regarding SDN operations. With the appropriate operation of the DER units in the SDN, losses can be reduced during normal operations and they can support local loads during abnormal conditions. Thus, the positive effects of the DER units need to be enabled in the SDN by adopting advanced operation schemes. In this paper, the smart control functions for the DER units in the SDN are defined and classified. In addition, the integration schemes for the SDN with DER units are introduced. The proposed operation strategies will be implemented into the Korean Smart Distribution Management System (KSDMS) as operation schemes used for loss reduction and service restoration. A sample case study shows the effectiveness of the proposed operation schemes to achieve smart operation functions for the SDN with DER units.

Design of Smart Distribution Management System for Obtaining Real-Time Security Analysis and Predictive Operation in Korea

The Development of smart grids offers new opportunities to improve the efficiency of operating and controlling distribution systems. It allows network operators to optimize the use of dispersed generation resources and enables real-time communication between customers and utility service providers to allow optimization and balancing of energy usage. Such an improvement in the flexibility and control of the distribution network is only possible if the control center operator has more accurate knowledge of the real-time situation of the network. The Korean Smart Distribution Management System (KSDMS) project was started in 2009 to achieve advanced distribution operation for potential smart grid systems in Korea. In this paper, we summarize two KSDMS design strategies for situational awareness in real-time distribution operation. One is the preparation of standardized data acquisition networks. In the KSDMS, numerous data related to the voltage, current, faults, power quality and load profiles of the network are gathered using a standardized communication method based on IEC 61850. The other is a real-time security analysis tools for smart distribution systems, designed to provide the distribution operator with accurate real-time situational information and predictive operation. We present a database design which can be used commonly for all security analysis programs in KSDMS.

An investigation of aging characteristics of polymer housed distribution surge arresters by accelerated aging test

The purpose of this paper is to verify the aging characteristics of domestic polymer housed distribution surge arresters. In this study accelerated aging test equipment was developed to simulate field condition of the distribution polymer housed surge arresters. Polymeric housing of distribution surge arresters should be degraded by environmental stress and the interface between housing and inner module can be affected by moisture ingress. This moisture absorption should increase leakage current and make tracking damage at the interface. Proposed aging test equipment can simulate UV, temperature, humidity, voltage, salt fog and rain and it can monitor total and resistive leakage current of arresters. In addition we carried out field exposure test at the outdoor test yard and characteristic analysis of field operated arresters. And then electrical performance of arresters, insulation condition of housing material and surface condition of the housing were compared.

The Coordinate Control Method of LTC Transformer and Capacitor Banks at Distribution Substation

The Load Tap Changing (LTC) transformer and Shunt Capacitor (SC) bank are major devices for voltage and reactive power control in a distribution substation. Thus, the coordination operation of a LTC transformer and a SC bank is required to achieve better voltage and reactive power compensation at a distribution substation in the same time. This paper proposes coordinate control method of LTC transformer and SC bank to achieve better voltage and reactive power compensation and operation times of these two devices in the same time. The mathematical formulations of the proposed coordinate control method are introduced. Sample case studies are shown to verify the effectiveness of the proposed coordinate control method.

Correlation between the AC breakdown strength and space charge distribution of water tree aged XLPE

To understand the electrical characteristics of water tree aged XLPE, artificially aged XLPE specimens of which the water tree with uniform length grew on the large area have been fabricated. The AC breakdown strength of the specimens has been reduced as the growth length increased and the trend of the reduction has been similar to that of water tree growth rate. Space charge distributions in the virgin and aged specimens have been measured by the PEA method and, as a result, it has been shown that the homo-charge is heavily concentrated at the tip of the water tree path while a little hetero-charge is gathered in front of electrode contacted to the water tree. Through the electric field calculation using the charge distribution, the local field enhancement at the tip of water tree path was also verified. Based on the experimental results and analysis, it can be said that the water tree reduces the breakdown strength of XLPE because of the homo-charge concentration at the tip of water tree path, which results in the reduction of effective insulating thickness.

A study on the oscillating wave voltage test as an after-laying test for distribution power cables

In this study, experimental investigation has been carried out for the defect detecting capability of two different way of the OW (oscillating wave) voltage test, such as with-cable-charging and without-cable-charging method. For this purpose, two types of OW voltage tests have been performed at the laboratory on the 22.9 kV CN/CV cables in which artificial needle-type and knifecut-type defects were well integrated. Based on the test results, it could be remarked that the with-cable-charging method is more appropriate to the after laying test due to its consistency of the test condition regardless of the cable length under testing.

The Characteristics of Winding Temperature for the Natural Ester Filled Transformer up to and Including 500 kVA

Because of environmental friendly and higher fire point, Natural ester fluids are widely used for transformer cooling materials. Natural ester has higher viscosity than that mineral oil. Top oil temperature and hottest temperature will be warmer when using natural ester fluid in transformers designed for conventional transformer oil. Although natural ester has less influence on deterioration of cellulose paper than mineral oil, an increased hottest temperature might have an effect on the aging of insulating paper in coil winding. When comparing natural ester with mineral oil at the same designed transformers up to 500 kVA. The deviation of hottest temperature between the two is increased with load. For preventing additional aging of insulation paper, design changes are required when substituting natural ester for conventional transformer oil.

An Optimization of the Distributed Generator Combination for Microgrid using Linear Programming

MG(Microgrid) is a small power supply system located on-site that can supply both the electricity and the hot-water simultaneously. Engineering S/W is requested to construct Microgrids economically. We developed Engineering S/W that can combine DERs (Distributed Energy Resources) most economically using the linear programming and estimate of the economic. Developed S/W was programed using GAMS(General Algebraic Modeling System) and it is composed of the optimal DER combination module and forecasting module of renewable energy`s output. We embody it based on MS Excel considering the user`s convenience and we show its validity through a case study. We think that developed S/W will be very useful for planning MGs and energy supply.

Thermal analysis of varnish treated insulating papers for transformers

This paper describes the thermal characteristics of varnish treated Kraft and aramid papers in order to understand the effect of the varnish concentration on the heat flow pattern. The insulating papers were impregnated by the varnish diluted with solvent and then dried completely. The heat flow of the specimens was obtained using a differential scanning calorimeter (DSC) and analyzed. As a result, the heat flow curves of varnish and varnish treated insulating paper linearly changed with the varnish concentration and it was confirmed that the varnish concentration could be determined by comparing with the changing patterns in heat flow of the varnish treated insulating papers with temperature.

Development of simulation platform of distribution systems with DGs and SVR for voltage control studies

In this paper, we develop the simulation platform of the distribution systems with distributed generations (DGs). The detailed simulation models of a DG and a step voltage regulator (SVR) are developed as PSCAD user defined model (UDM). The control schemes of SVR and DGs to regulate the local voltages are proposed and implemented as a function block in the PSCAD platform. Some case studies to verify the effectiveness of the control schemes are performed in the developed simulation platform.