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This paper presents the results of a study of a voltage management technology called parameter determination of voltage regulator (PDVR) implemented in a 22.9 kV distribution network. Korea Electric Power Corporation has developed this PDVR technology for increasing the hosting capacity without causing any voltage problems in LV (220/380 V) networks. PDVR calculates and provides the operation settings of voltage regulators such as on load tap changer, pole mounted automatic voltage regulator, and distributed generation (DG). Subsequently, these settings are applied to the voltage regulators, which further optimize the 22.9 kV network voltage without the control of the distribution management system (DMS). A study of the operations and performance of PDVR through the analysis of test results is presented in this paper.

This study is aimed at determining the optimal energy storage system (ESS) operation schedule to minimize the peak load on the feeder of a distribution network. To reduce the peak load, the feeder load profile needs to be predicted. A deterministic prediction is not reliable, however, because it may contain errors. This study proposes the use of prediction intervals (PIs) of estimated error based on prior predictions. The proposed algorithm is intended for the determination of an optimal ESS schedule using the PIs. To demonstrate the method’s validity, a case study is presented where a proposed optimal ESS schedule determined from PIs reduces the peak load during network operations over a one-year period. The performance of the proposed method is superior to that of the conventional method which uses deterministic load prediction.

With an increase in the mount of photovoltaic (PV) generators in a distribution network, the network requires flexible energy storage systems (ESSs) to accept additional PVs and prevent power overflow. This paper aims to find the best ESS operation schedule to minimize the peak load on the feeder. The load on the feeder needs to be predicted to determine the optimized ESS schedule; however, one deterministically predicted scenario is not reliable because the prediction contains certain error. In this paper, the forecasting error is reflected when the ESS schedule is optimized by using probabilistic load prediction. The proposed method doesn’t provide only one scenario but shows various scenarios with probability of peak load to distributed network operators (DNOs) as a result of ESS operation. The DNOs can choose the best scenario based on their principles. In the simulation, based on the probabilistic load prediction, the peak load is shaved and three scenarios—optimistic, realistic, and pessimistic—are shown.

A distribution system was designed and operated by considering unidirectional power flow from a utility source to end-use loads. The large penetrations of distributed generation (DG) into the existing distribution system causes a variety of technical problems, such as frequent tap changing problems of the on-load tap changer (OLTC) transformer, local voltage rise, protection coordination, exceeding short-circuit capacity, and harmonic distortion. In view of voltage regulation, the intermittent fluctuation of the DG output power results in frequent tap changing operations of the OLTC transformer. Thus, many utilities limit the penetration level of DG and are eager to find the reasonable penetration limits of DG in the distribution system. To overcome this technical problem, utilities have developed a new voltage regulation method in the distribution system with a large DG penetration level. In this paper, the impact of DG on the OLTC operations controlled by the line drop compensation (LDC) method is analyzed. In addition, a generalized determination methodology for the DG penetration limits in a distribution substation transformer is proposed. The proposed DG penetration limits could be adopted for a simplified interconnection process in DG interconnection guidelines.

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.

MicroGrids are small power supply system located on-site that can supply both the electricity and the hot-water simultaneously. MicroGrid system that consists of Distributed Energy Resources system, such as wind, solar, fuel-cell and co-generation, has been developed greatly during the last 10 years. It's concept assumes a cluster of loads and microsources operating as a single controllable system that provides a new paradigm for defining the operation of distributed generation. For example this cell could be controlled as a single dispatchable load, which can respond in seconds to meet the needs of the transmission system. It can be also designed to meet their special need; such as, enhance local reliability, reduce feeder losses. This paper introduces the case study of engineering to construct Microgrid with actual loading in KEPRI

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.

Maximum Power Point Tracking (MPPPT) techniques are employed in PV systems to make full utilization of PV array output power which depends on solar irradiation and temperature. Recently, many MPPT algorithms and control schemes of PV system have been proposed, but different control methods and different PID controller parameters lead to different output efficiency and dynamic response. Therefore, in this paper, a PSCAD/EMTDC user defined module of the solar array is established to easily simulate its inherent characteristics with the basic specification data. Moreover, we also compare the advantages and weakness of the existing MPPT control methods by simulations to give a reference to the Grid-Connected Photovoltaic System (GCPS) designers.

The generating systems use Doubly-Fed Induction Generators (DFIGs) to achieve high conversion efficiency and to reduce the installation cost. This paper presents a modeling and Maximum Power Point Tracking (MPPT) control method of DFIG-based variable-speed wind energy conversion system. The generator considered is a wound rotor induction machine whose stator is connected directly to the grid and the rotor is fed through back-to-back Pulse-Width Modulation (PWM) converters. Stator flux-oriented vector control is applied to control the active and reactive current loops independently. The MPPT control method in a Wind Energy Conversion System (WECS) is proposed. The proposed control solution aims at driving the position of the operating point near to optimality. This is a very important aspect to maintain DFIGs efficiently in a variable wind speed. The wind generator is modeled in RSCAD program which is interfaced with the Real Time Digital Simulator (RTDS).

Penetration of distributed generator(DG) to power distribution system can cause malfunction of existing protection schemes. Because grid interconnected DG can contribute fault currents and make bidirectional current flows on the system, fault contributions from DG can cause an interference of protection relay operation. Therefore, over current protection device of the distribution system with DGs need directional protection schemes. In this paper, improved directional protection algorithms are proposed for the distribution system with DG considering their fault characteristics. And than, these directional protection algorithms are tested and validated in various fault conditions. From the simulation results, it can be seen that the proposed directional protection algorithms are practically efficient for the radial distribution system with DG.

Tapered roller bearings are core components of rotating machine parts and are simultaneously subjected to axial and radial loads. Life-shortening effect was particularly evident in the case of tapered roller bearings used in the input and output shafts of transmission; this shortening of life was a result of excessive axial pre-load, which is common in the transmission assembly line. In this study, we derived an equation for evaluating the life of tapered roller bearings subjected to excessive pre-load by using accelerated life test data. The DOE(Design Of Experiment) method and FEA(Finite Element Analysis) was used for determining the condition for performing an accelerated life test. This equation for evaluating the service life of the bearings was derived by analyzing the Weibull distribution of the test results. Using the derived equation the life evaluated was 6-7 times longer than that evaluated by the conventional bearing-life equation. The results of this study will be helpful in predicting the life of tapered roller bearings subjected to excessive pre-load and in designing reliable rotating machines.

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.

It is expected that distribution system, interconnected with wind turbines, would experience the voltage problem due to WT`s output. But most papers just consider this problem using the simulation or the theory only. In this paper, we verify this problem through the measurement at the distribution system and wind turbine. We explain the method for voltage management at distribution system. And we verify that the voltage of D/L interconnected with WTs could not be maintained properly using pole transformer`s tap only. We consider some method to solve this problem and we propose the installation of SVR(step voltage regulator). Finally we show this method`s validity through the simulation.

As the penetration of distributed generation systems is recently high, there have been metering errors, trips of protective devices in KEPCO distribution systems including an occurrence of false fault-indicator in distribution automation system. The cause of malfunctions was the reverse-power-flow phenomenon due to transformer wiring types. By the effect of the reverse-power-flow, each of phase`s fundamental currents was added by about 3 times on the neutral line. A new method based on the analysis of the reverse-power-flow is proposed in this paper. Fault currents on each section were analyzed by the proposed method, and the effect of types of transformer wiring was examined experimentally. In order to reduce the malfunctions due to the reverse-power-flow, controlling the zero-sequence impedance of transformer was designed and verified by using PSCAD/EMTDC software.

Korea Electric Power Corporation (KEPCO) developed a Korean Smart Distribution Management System (K-SDMS) to address many issues of distribution system control, including the lack of receptivity of distributed generations (DGs). Voltage-VAR control (VVC) program is one of the K-SDMS real-time mode applications. VVC calculates the references of voltage and reactive power control equipment, which minimize the power loss while satisfying a number of operational constraints. The VVC application is upgraded to have a new control objective, i.e. conservation voltage reduction (CVR). CVR is based on the simple premise that reduction of the voltage will lead to reduced energy consumption by the end-use loads. This paper presents the algorithm of developed CVR function and the test results. The CVR function calculates the references of the voltage control devices such that the bus voltages are maintained at as close to the lower operation limit as possible. Firstly, the system is divided into small sections. Secondly, the reactive power references of the DGs are determined such that the voltage profile of the section is flattened. Finally, the tap references of the on-load tap changers (OLTCs) and step voltage regulators (SVRs) are calculated. The effectiveness of the CVR is presented with case studies using the K-SDMS simulator.

Durability assessment for the suspension system of the vehicle is very important. Particularly, corrosion fatigue strength of coil spring depends on many factors including mechanical and environmental properties. In this paper, residual stresses by multiple shot peening were analyzed using finite element analysis, and evaluated its effect on corrosion fatigue strength. And also, a corrosion fatigue design criterion for coil spring of light commercial vehicle (LCV) based on proving ground response was proposed.

In this paper, the effects of the residual stresses on the life of structural engineering components were investigated to predict the wear-life. Residual stresses are usually created by the surface treatment, such as shot peening or deep rolling. The objective of the experimental investigation was focused on the influence of friction and wear characteristics due to the residual stress under dry sliding condition and the measurement of the interleaf friction. Test specimens were made of SUP9, the leaf spring material. The residual stresses were created on their surface by shot peening treatment. Residual stress profiles were measured on the surface and subsurface by means of X-ray diffraction method. Also, the sliding tests were carried out under the different contact pressure and the same sliding velocity of 0.035m/s in order to investigate the friction and wear characteristics of leaf surfaces. Leaf spring assembly tests were performed by the ultimate tensile machine with sticking strain gauges on the leaf surfaces in order to evaluate interleaf friction characteristics. We compared friction coefficients, wear volumes and wear rates of the shot-peened specimens with those of the unpeened specimens, and evaluated the effects of residual stress on the tribological characteristics. We obtained the load-displacement curves, and measured interleaf friction force and interleaf friction coefficient of leaf spring assembly from these curves.

Suspension system of light commercial vehicle (LCV) has enough endurance to protect passenger and freight. Leaf spring is major part of LCV suspension system. Thus, fatigue strength evaluation of leaf spring based on road load response was carried out. At first, the strain of leaf spring was measured on the city mode driving condition and proving ground driving condition. And , the damage analysis of road load response was carried out. After that, fatigue test of leaf spring was also carried out. Based on ε-N life relation, fatigue life of leaf spring was evaluated at Belgian mode, city mode and drawing test specification called the 3 steps test mode. Next, it is compared the design life of leaf spring and evaluated fatigue life by the 3steps test mode. From the above, new target of Belgian mode and city mode was proposed to gratify design specification of leaf spring. It is expect that the proposed target can be satisfied leaf spring fatigue endurance at specific road condition.

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.

The grid-interconnected Microgrid must be able to operate without the utility's grid to supply electricity in case of outage. To operate in standalone mode, the Microgrid must control electricity demand or supply to maintain the frequency. The Microgrid EMS (Energy Management System) could control supply and demand with the AGC (Auto Generation Control) function using a communication line. Note, however, that the period of AGC is too slow to maintain the frequency if there is rapid variation in loads or generation. Moreover, the transition of operation mode could fail if there is too much power flow at PCC (Point of Common Coupling). In this paper, we propose a method of improving the stability of the grid-interconnected Microgrid using BESS (Battery Energy Storage System) and super capacitor. The cooperative control method between BESS and super capacitor uses droop, which is used at the generator. BESS could operate as UPC (Unit Power Control) or FFC (Feeder Flow Control) depending on Microgrid's operation strategy. We simulate the cooperative control method using PSCAD/EMTDC to verify the validity of the method. As a result, Microgrid's stability is improved using the cooperative control method, and the life span of BESS could be prolonged.

The interconnection standards/guidelines have been designed to prevent unfavourable interconnection problems of the DG (Dispersed Generations). Therefore, in practice, unit or cumulative interconnection capacity for particular voltage levels have been be limited to maintain admissible power quality and reliability. Recently, the interconnection standard/guidelines in South Korea are revised at Feb. 2012. In this paper, we briefly introduce the revised version of the DG interconnection standard/guidelines in South Korea and technical solutions/recommendations for large penetration of DG in the KEPCO (Korea Electric Power Company) distribution network. (4 pages)

Penetration level of distributed generation (DG) on the grid is increasing worldwide. For the connection of new DG to the distribution network, various factors are considered including technical requirements that ensure the DG does not adversely affect the operation and safety of the network. Distribution system operators (DSO) have to perform impact studies of DG but these studies need cumbersome modeling and simulating of the target distribution network whenever DG is connected and the long time required for technical review. Therefore, utility engineers need the screening methods that can straightforwardly indentify cases with no impact on distribution system or those applications requiring detail studies. This paper presents the screening process and evaluation methods with simple rule on bank level and feeder level, respectively.

During the last decade, the needs for exploitation of distributed generation (DG), including renewable energy such as photovoltaic, wind turbine, fuel cells, etc., has been growing. In spite of many economic and technical advantages of DG, high penetration of DG in distribution systems would cause some negative impacts on distribution network operation such as increase of fault current level, false tripping, etc. In this paper, the impacts of DG's on protection coordination and operation of distribution network are analyzed including increase of the level of fault current, malfunctioning of protective devices and protection coordination of CB-reclosers. And Test of directional recloser and directional distribution automation FRTUs is also carried out to validate the directional elements and fault indication function of these bidirectional devices using real-time power system simulator. These directional overcurrent elements and fault indication of bidirectional devices are tested and is validated in various fault condition in distribution network with distributed generation using real-time power system simulator. (5 pages)

This paper proposes a reliable and effective voltage control method using modified voltage droop control in low voltage (LV) distribution system when serious voltage problem occurs. The proposed method changes the droop control mode from conventional droop control to modified droop control and vice versa. It determines mode change condition to maintain the point of common coupling (PCC) voltage within voltage dead band. The numerical expressions of Ihe proposed method are presented and it is verified through the corresponding PSCAD based computer simulation.

Among durability tests, the accelerated durability test has been widely used to evaluate the durability of vehicle structure and chassis parts in a short period of time on the designed road which has severe surface conditions. However it increases the driver's fatigue mainly caused by the severe driving conditions. The driver's difficulty of maintaining constant speed reduces the reliability of test results. The durability test includes the position and distance sensing system for the recognition of the absolute and relative driving position, the driving control system for the control of whole driving circumstance, the emergency and multisafety system for responding to system errors and the camera system for monitoring driving circumstances during the test. AGVDS (Autonomous Guided Vehicle Driving System) was proved to facilitate the development of new car projects. Therefore the AGVDS we propose will help make the fundamentals for all future traffic systems.