Won-Sik Moon

A Study on the Application of a Superconducting Fault Current Limiter for Energy Storage Protection in a Power Distribution System

This paper presents the application of a superconducting fault current limiter to energy storage for protection in a power distribution system. An energy storage system is increasingly being used to help renewable energy resources integrate into the grid. It is important to keep an energy storage system interconnected with the grid without interruption and to supply electrical power to the grid. The main objective of this paper is to introduce a superconducting fault current limiter to keep the energy storage system from disconnecting from the grid when ground faults occur. Its effect is analyzed using transient simulation software.

Ignition Characteristics of Residential Series Arc Faults in 220-V HIV Wires

Unintentional arc faults, caused from damaged power line cords and loose connections, can start a serious fire and safety hazard in residential areas. The arc fault circuit interrupter (AFCI) is beginning to emerge as a product to protect against the arc that may cause fire. In this paper, we analyze ignition characteristics depending on the magnitude of load current when series arc occurs. Also, we suggest the suitable arc clearing time based on characteristic analysis in Korean residential electric environment. To do this, we have tested the carbonized path arc clearing time test using ultraviolet signal detecting system according to the test method of UL 1699. As wire specimen in those experiments, we used the heat resistant indoor PVC insulated (HIV) wire which is a kind of residential electric wire.

A Study on Siting of HVAC Offshore Substation for Wind Power Plant using Submarine Cable Cost Model

Development of the technologies for offshore wind power is proceeding actively and the installation capacity is continuously increasing because of its many advantages in comparison with the land wind power. Accordingly, project for Southwestern 2.5GW offshore wind power plant is in progress in Korea. Design of electric power systems for offshore wind power plant is very important due to its high investment and operational costs. Hence, it needs to be designed in order to minimize costs. This way can be employed in determining the installation location of offshore substation for HVAC wind power plant. According to the offshore substation site, MV inter-array cable and HV export cable lengths vary and they change a total cost regarding submarine cable. This paper represents cost models with variables which are MV inter-array cable and HV export cable lengths to locate the offshore substation for HVAC wind power plant. It is classified into submarine cable installation cost, reactive power compensator installation cost, ohmic losses, and unsupplied energy cost. By minimizing a total cost, an appropriate installation site of the offshore substation is determined.Development of the technologies for offshore wind power is proceeding actively and the installation capacity is continuously increasing because of its many advantages in comparison with the land wind power. Accordingly, project for Southwestern 2.5GW offshore wind power plant is in progress in Korea. Design of electric power systems for offshore wind power plant is very important due to its high investment and operational costs. Hence, it needs to be designed in order to minimize costs. This way can be employed in determining the installation location of offshore substation for HVAC wind power plant. According to the offshore substation site, MV inter-array cable and HV export cable lengths vary and they change a total cost regarding submarine cable. This paper represents cost models with variables which are MV inter-array cable and HV export cable lengths to locate the offshore substation for HVAC wind power plant. It is classified into submarine cable installation cost, reactive power compensator installation cost, ohmic losses, and unsupplied energy cost. By minimizing a total cost, an appropriate installation site of the offshore substation is determined.

A Selecting Method of Optimal Load on Time Varying Distribution System for Network Reconfiguration considering DG

This Paper presents about selecting the most suitable load used for distribution optimization considering time-varying load demand and generation of DG. The objective of this paper is to find optimal load which obtain best network reconfiguration result according to time-varying load demand and DG generation. Many researches about distribution reconfiguration for optimization have been studied for ages and they have used constant loads only for reconfiguration. To get the best result, however, at least for 24 hours time-varying load demand and generation of DG should be considered. Four daily load curves and one PV generation curve have been decomposed into sequential levels. But, the optimal distribution reconfiguration considering time-varying load demand and PV generation should not to be the only scheme. Because, the reconfiguration result may demand hourly switching operation of electric devices and it might cause deterioration of switches lifespan. Therefore, the method of how to select the most optimal load considering not only time-varying loads demand and DGs generation but also the number of switching for maximizing income is researched. The method of selecting optimal load is proved by adapting to a simple model system and the more efficient result is also confirmed in this paper.

DC-link Voltage Control of HVDC for Offshore Wind Farm using Improved De-loading Method

This paper presents the DC voltage control method in DC link of High Voltage Direct Current(HVDC) for an offshore wind farm in Low Voltage Ride Through(LVRT) situation. Wind generators in an offshore wind farm are connected to onshore network via HVDC transmission. Due to LVRT control of grid side inverter in HVDC, power imbalancing in DC link is generated and this consequentially causes rising of DC voltage. A de-loading scheme is one of the method to protect the wind power system DC link capacitors from over voltage. But the flaw of this method is slow control response time and that it needs long recovery time to pre-fault condition after fault clear. Thus, this paper proposes improved de-loading method and we analyze control performance for DC voltage in LVRT control of HVDC for an offshore wind farm.

Transformer capacity evaluation of offshore wind farm substation applied to Korean site

An Offshore wind power system is very expensive and different from that of onshore in many ways. There has been a continuous increase in the capacity of the offshore wind farms (OWFs). It is essential to analyze the availability and reliability to optimize the redundancy of OWFs. This paper presents a probabilistic reliability evaluation to determine the number of transformers and that of capacity on offshore AC substation. The proposed approach is based on probabilistic model of wind energy that combines the wind speed with output characteristics of the wind turbines and the overall economic cost model. The economic evaluation is applied to actual wind speed at the southwestern coast of the Korea and their application results are suggested.

Grid optimization for offshore wind farm layout and substation location

The investment and operation costs of offshore wind farms (OWFs) are very high because the level of technology is still at an infancy stage as well as because of the marine conditions. Therefore, reducing the design costs of a power grid system for OWFs is very important for economic feasibility. In particular, optimizing the layout design of a wind farm system is needed to minimize the project cost. This study deals with an optimization programming of an electric power system layout for OWFs with offshore substation. The proposed optimization method can reduce the total layout cost lower compared with existing methods. A genetic algorithm is used as an optimization method, and an algorithm for layout optimization is presented. On the basis of this method, a case study is conducted to compare our proposed method with the existing methods by simulating a 100-MW OWF.

Control Scheme Using Active Power Regulation for DC Voltage of VSC HVDC Under Unbalanced Voltage

Faced with unbalanced grid operation mode, the high voltage direct current (HVDC) based on voltage source converter (VSC) can be properly controlled by a dual current control scheme. For the modular multilevel converter (MMC) controlling the AC side current is able to limit the arm current which flows along the IGBT of submodule (SM) to rated current. However the limitation of the arm current results in leaving the control range of active power at MMC confined to below the rated capacity. As a result, limiting the arm current causes the problem that the DC side voltage of the HVDC can not be controlled to the reference value since MMC HVDC adjusts the DC side voltage through the active power. In this paper, we propose the algorithm adjusting the active powers of both MMCs to resolve the problem. The back-to-back MMC HVDC applying the algorithm is modeled by PSCAD/EMTDC to verify the algorithm.

Optimal Design of Power Grid and Location of Offshore Substation for Offshore Wind Power Plant

Abstract – This paper presents the methodology for optimal design of power grid for offshore wind power plant (OWPP) and optimum location of offshore substation. The proposed optimization process is based on a genetic algorithm, where the objective cost model is composed of investment, power loss, repair, and reliability cost using the net present value during the whole OWPP life cycle. A probability wind power output is modeled to reflect the characteristics of a wind power plant that produces electricity through wind and to calculate the reliability cost called expected energy not supplied. The main objective is to find the minimum cost for grid connection topology by submarine cables which cannot cross each other. Cable crossing was set as a constraint in the optimization algorithm of grid topology of the wind power plant. On the basis of this method, a case study is conducted to validate the model by simulating a 100-MW OWF.Key Words : GA optimization, Probabilistic wind power model, Offshore su bstation, Offshore wind power grid, Submarine cable crossing†Corresponding Author : School of Electrical Engineering, Soongsil University, KoreaE-mail : jckim@ssu.ac.kr* School of Electrical Engineering, Soongsil University Korea** KEPCO Research Institute, KoreaReceived : June 9, 2915; Accepted : June 25, 2015

A Study on the Adequate Capacity of Substation Transformer for Offshore Wind Farm

This study suggests the methodology to decide the number and adequate capacity of substation transformer in a large-scale offshore wind farm (OWF). The recent trend in transformer capacity of offshore substation is analyzed in many European offshore wind farm sites prior to entering the studies. In order to carry out the economic evaluation for the transformer capacity we present the cost models which consist of investment, operation, and expected energy not supplied (EENS) cost as well as the probabilistic wind power model of wind energy that combines the wind speed with wind turbine output characteristics for a exact calculation of energy loss cost. Economic assessment includes sensitivity analysis of parameters which could impact the 400-MW OWF: average wind speed, availability, discount rate, energy cost, and life-cycle.