Current Status and Future Prospect of Korean Power Distribution ...

Current Status and Future Prospect of Korean Power Distribution SystemSang-Seung Lee* 1 , Jin-Man Sohn* 2 , Kwang-Jae Song* 2 , Tae-Jin Kwon* 2 , Jong-Keun Park* 2 , Song-Keun Lee* 3Korea Electrical Engineering & Science Research Institute,130-Dong, Seoul National University, Shinlim-9Dong, Kwanak-Gu, Seoul, 151-742, Rep. of Korea* 1School of Electrical Engineering,301-Dong, Seoul National University, Shinlim-9Dong, Kwanak-Gu, Seoul, 151-742, Rep. of Korea* 2Electrical Engineering,Jeonju university, Jeonbuk, Rep. of Korea* 3AbstractThis paper will present the current status and future plans pertaining to power distribution system in South Korea. Currently, thepower transmission voltages in South Korea are 345kV on major networks, 154kV or 66kV in local systems, and powerdistribution voltages are 22.9kV or 3.3kV in regional or local systems. The power system on Jeju Island is now connected to themainland via a 100km-long submarine transmission system composed of HVDC (High Voltage Direct Current) cables. The SouthKorean power system is divided into 7 geographical areas, taking into account the geographical boundaries, which are Gyeonginnorthern area, Gyeongin southern area, Yeongdong area, Jungbu area, Yeongnam area, Honam area, and Jeju Island area. Theregional characteristics are complex, with mixtures of mountainous areas and flatlands. In South Korea, the distribution lines havebeen composed of radial systems, with the exception of one large city and major facilities. In addition to, most of the distributionlines have been constructed in line with both sides of the streets along with state roads and local roads. In this paper, we propose afuture plan for Korean power distribution system, which appears to complex and various forms mixed with mountain areas and flatregions according to geographical characteristics.Keywords: Korean Power Distribution System, Current Status and Future Prospect, Radial and Loop System1 INTRODUCTIONCurrently, the power transmission voltages in South Korea are345kV on major networks, 154kV or 66kV in local systems,and power distribution voltages are 22.9kV or 3.3kV inregional or local systems. The power system on Jeju Island isnow connected to the mainland via a 100km-long submarinetransmission system composed of HVDC (High VoltageDirect Current) cables. The total length of the transmissionlines is 25,337C-km and the total capacity of substationfacilities has been expanded to 120,257MVA. Powertransmission networks and substations are monitored andcontrolled by SCADA (Supervisory Control And DataAcquisition) systems. These systems have T&D(Transmission & Distribution) facility improvement andcontrol automation, which includes installing more indoor andunmanned substations to enhance power supply reliability[1-4].Also, static condensers have been installed at 154kVsubstations in order to compensate for the voltage drop of thesystem during heavy load periods. The regulation of adistribution line voltage has adopted automatic ULTC (UnderLoad Tap Changer) operation in order to maintain a constantvoltage level. Considering the environmental sites in urbanareas, 345kV underground lines are being extended to makeloop systems. Civil structures that use various undergroundtransmission cable are ducts, culverts and tunnels. Theculverts have been increased recently due to increasingelectric power demand and the need for installation of anumber of cables in the same route.Especially in the downtown areas, more tunnels are being builtdue to the demand for more roads of the local government.Since 1995, XLPE (Crosslinked Polyethlene) cable has beenused exclusively for 154kV underground transmissionfacilities with some exceptions, (connection to existing OFcable) because of environmental considerations and lowoperating costs due to the simplicity of the cable system incomparison with traditional oil filled cables. In the future,XLPE cable will be used for 345kV, and local cable makersare actively engaged in the development of the 345kV XLPEcable.KEPCO sold 32,732GWh of electricity in 1980 and electricitysales reached 278,451GWh in 2002, which is a 8.5-foldincrease in 20 years. Annual sales during the past decade haveaveraged 10% annual growth, except for a decline in growth

in 1998 due to the economic crisis. On the other hand, 10.7%growth was recorded in 1999 with the recovery of theeconomy. This economic recovery further boosted electricityconsumption in 2000 to a record 11.8% yearly increase.However, the economic downturn during 2001 and 2002stunted electricity sales growth rates to 7.6% and 8%,respectively. The per capita consumption of electricity stalledat 859kWh in 1980. The figure that leaped to 5,444kWh by2002 was boosted by continuous economic expansion.Considering the foregoing data, Korea still has very highgrowth potential for electricity sales compared to the percapita consumption in advanced countries. Sales revenue in2002 exceeded 20.57 trillion won, a 3.6% increase from 2001.At the same time, the average sales unit price, i.e. salesrevenue divided by sales volume, was 73.88 won/kWh, down4.1% from 2001. The breakdown of electricity consumptionwas 51.9% by industry, 33% by the public and service (mainlycommercial) sectors, and 15.2% by residential customers.Nowadays, the consumption trend in Korea shows a movetoward the typical consumption types of advanced countries,as the proportion of industrial use decreases while householdsare taking up a greater proportion of the total consumption.The overall power system is divided into 7 geographical areas,taking into account geographical boundaries, which areGyeongin northern area, Gyeongin southern area, Yeongdongarea, Jungbu area, Yeongnam area, Honam area, and JejuIsland area. The regional characteristics are complex, withmixtures of mountainous areas and flatlands.The distribution lines are composed of radial systems, with theexception of one large city and major facilities. And most ofthe distribution lines have been constructed in line with bothsides of the streets along with state road and local roads. Thiscan make easy for its restoration and extension by car. Theoperation of distribution system has been done and maintainedthrough 15 parts of local branch offices and 185 parts of localbusiness offices. There make a point of replacing an overheadline by an underground cable for a large city or downtowns[1-4].This paper prospects and proposes a future plan for Koreanpower distribution system, which appears to complex andvarious forms mixed with mountain areas and flat regionsaccording to geographical characteristics.2 Current Status of Korean Distribution SystemKEPCO (Korea Electric Power Corporation) is committed tocontinuously improving essential power distribution facilities.Special attention are begin given to developing new materialsthat can enhance the efficiency of distribution equipmentinstallation, durability, and reliability, while reducing costs.Currently, KEPCO is developing amorphous transformers andenergy-saving transformers to reduce power loss. A project isalso under way to develop fiber reinforced plastic poles thatweigh less by 70% than concrete poles do.The R&D program also extends to plastic cutout switchcross-arms and insulated high-voltage power cables thatreduce power failures caused by various bird species. Inaddition, KEPCO is developing distribution equipment andmaterials that minimize environmental impact. Someexamples are epoxy-molded ground-transformers and switchesthat do not require insulation gas or oil. Old concrete poles arecrushed and recycled for use in building concrete manholesand for other purposes. A new power distribution test center iscurrently conducting tests to verify the performancecapabilities of these newly developed materials and equipment.In addition, a project is underway to develop advancedelectro-magnetic meters that can be read wirelessly andremotely. Modern industrial society must be supported byuninterrupted electrical power supply. To this end, KEPCOconstantly engages in constant preventative maintenance anddeveloping new engineering methods to reduce power outageswhile working on building more distribution lines.KEPCO is trying to enhance network stability by theexpanded use of highly reliable equipment and materials suchas heat-resistant insulated cable and maintenance-freeswitches. For example, aerial bundled cables and spot-networkdistribution approaches are being adopted to avoid blackouts.State-of-the-art detectors such as infrared thermal imaging arealso being used for locating vulnerable spots in thedistribution system and address potential problems in advance.When a breakdown occurs in the system, the trouble spot canbe automatically pinpointed to reduce blackout time andaffected area. Such extensive preventive efforts have ensuredreliability in distribution system operations as shown in theperfect power supply major events including the 2002Korea-Japan World Soccer Games and Busan Asian Games.In 2002, the average blackout time per customer was 19minutes, which puts South Korean among the top rankingperformances in the world. KEPCO is building highly reliablepower distribution networks to ensure stable power supply.Power distribution line length stood at 366,944 C-km by theend of 2002 and supports surpassed 6.88 million units. 9.7%of high-voltage lines were under-grounded nationwide and46.8% was buried in the Seoul metropolitan area.Table 1. Distribution facilities in South KoreaFacilities/equipmentLine length(C-km)Transformers(kVA)Supports(units)‘2000 351,264 57,178,373 6,439,229‘2001 358,328 65,035,173 6,694,899‘2002 366,944 71,977,545 6,875,448In general, the distribution networks are composed of22.9kV-Y multiple-grounded lines. Power supplied tolow-voltage end-users is supplied via either the 220V or 380Vlines. KEPCO began upgrading low-voltage lines since the1960's to increase supply capacity. The voltage supply hasbeen upgraded by 100% for households and 99.9% for

high-voltage distribution network lines. Meanwhile, the use oflow power-loss materials such as aluminum clad steelreinforced aluminum wires and transformers with amorphouscores or with G-6 iron cores is being boosted to reduce powerloss.Figure 1. Growth in electricity salesBy the end of 2002, the distribution power loss rate stood at1.75%, while voltage requirements were met 99.9% for theyear. These figures show that KEPCO's distribution networkoperations are outstanding, even when compared withadvanced countries. KEPCO has also installed automatedpower distribution systems to meet the needs for high-qualitypower supply required by sensitive equipment in the IT era. Atthe same time, KEPCO continues to develop new networkoperation technologies and alternative systems such aswind-powered generation.3 Prospective View for Future Distribution System3.1 Interconnection standard of distribution resourceKEPCO (Korea Electric Power Corporation) has completedtwo projects. One is distribution automation and the other isnew energy resource. First, KEPCO has ensured the operationtechnique and the standard of system interconnection aboutthe new energy with which is photovoltaic-power,wind-power and etc as follows.- In August 2003, a public hearing attended bygovernment officials, wind-power operator, academicworld was held. For reference, the effect of distributedresource to power system is voltage regulation andharmonic generation, the disturbance of protectioncoordination.- In December 2003, KEPCO reformed the distributedresource voltage interconnection standard and haveapplication to the standard.The basic principles of system interconnection in distributedresource are as follows: First, reverse power flow ofdistributed resource flows in system interconnection changingfrom existing one directional power flow. Second, the changeof the power quality when the parallel or separation ofdistributed resource occurs. When system interconnection isoperating in parallel, the voltage in interconnection point rises,and when it is separating, voltage drops. The electric businessoperator is responsible for maintaining the electric quality inthat distributed resource remains connected. The capacity ofgeneration facility to interconnect a distribution line can beregulated below the lowest load. The application object is asubstation of above 66kv and a substation with private supplyof 22.9kV. The tolerance standard with voltage distortion is3% above 66kV and 1.5% above 154kV.- In April 2003, we measured and analyzed theharmonics flowing in distribution system.- From July 2003 to August 2003, we measured sampleharmonics in distribution line, and August 2003, werenewed the standard for transformer neutral line andthat for interconnection of single-phase transformer.- In September 2003, we discussed with substation relayTAP transmission substation and finished building thefirst step upward control.- In September 2004, we established a tolerance standardof harmonics flowing in distribution system andrenewed the supply agreement. This reduced to 27.3%compared to last year in ill-defined fault. This ispossible because we protect the drop of electric qualityand large scale black out. We also studied the harmfuleffects in electric home appliances and industry.- In September 2002, we studied the effect of instantvoltage variation and, instant black out.- In August 2003, we established the standard of voltagemanagement and low voltage distribution equipment.We also determined the basis of treating commoncomplaints and ways to enhance in voltage quality.3.2 Wind-power generationWind-power has synchronization, repeat separation and outputvariation according to the change in wind velocity. Whenwind velocity exceeds 4m/s, the generation output (about 5%)is the lowest. But when wind velocity is 13∼25m/s, thegeneration output is 100%. When wind velocity is below 4m/sor above 25m/s (5minutes continuation), the generation stops.The effect on interconnecting wind-power is the systeminterruption of voltage flicker and the difficulty normalvoltage management of the interconnection line. Also, thesystem interruption of voltage flicker is caused by inrushcurrent, which is produced by frequent parallel-separation.Such effect is being investigated by the various distributionoffice. KEPRI (Korean Electric Power Research Institute) issupplying reliability (improvement), the quality of the power(voltage, frequency, power factor), the security of worker, theassistance of power supply equipment and other consumer.First let us look at the Jeju case. The Hang-won wind-powersystem interconnection operation can be summarized asfellows.- In February 1998, we are cooperative request ofpracticable business for Jeju wind power generation.

- In March 1998, we installed first power systemconnection of Hangwon wind power of 1,200kW withconnection line of 66kV Jeocheun S/S and GimyeoungD/L.- In July 1998, we requested for complementarymeasures of producing power of Hang-won wind powergeneration. (MOCIE)- In February 2000, we are connection of increasingHangwon wind power to 3,045kW and cumulative sumto 4,245kW.- In July 2000, we are request for connectingexamination of Hang-won wind power of 1,320kW andcumulative sum of 5,565kW. (Jeju provincial office →KEPCO)- In January 2001, we are notification of connectingmethod and connection to Seungsan substation bus byinstalling a 22.9kV-Y private line.- In April 2001, we convened the organization meetingfor power system connection methodology of Hangwonwind power. Subscription of increasing of Hangwonwind power was 1,300kW. (Jeju provincial office →KEPCO)3.3 Distribution system voltage controlA 23kV substation output voltage control & improvement inover-voltage can be summarized as follows:- In January 2003, it checked the substation outputvoltage used to establish aid-system with relation partand transmission and substation part of existing23.8~22.7kV within +4 ~ -1%. It ranged within±2.5% after increasing to 23.5~22.4kV.- In February 2003, it was applied to 4 substations and 12primary transformers for achieving output voltagecontrol.- In April 2003, the entire nation’s 228’ distributionsubstations and the 674’ primary transformers arefinished for output voltage control. This brought abouta 53% reduction of over-voltage-rate compared withlast year.Table 2. Distribution system voltagePrimaryVoltageSecondaryVoltage’03 working status (%)Business contentsTarget yearTarget Result GoalPrimary6.6kV→22.9kV 99.9 99.9 100 ’04 CompleteboostSystem22kV→22.9kV 5unitD/L 5unit D/L 100 ’08 CompleteUnification220V110/220V→220V 99.0 99.4 100 ’05 CompleteUnificationPower200V→380V 99.5 99.7 100 ’05 CompletebootSimple organization of distribution system voltage of theeffects of operating the can be summarized as follows. Theefficiency of system operating through the simplification ofsystem equipment rises. The supply capacity rises and the lineloss through the simplification of the voltage-supply-waydecreases.3.4 Operation plan of distribution system capacityWe are fundamental and reform standard of distributionautomation switch. We are distribution automation primaryequipment finished to supply. We increase the capacity ofoperation distribution line from 7,000kVA to 10,000kVA.With the increase of large apartment building, stores, hospitals,etc., we need to optimize the distribution system.Table 3. Plan of operation capacity of distribution systemClassificationA region(big city)B region(medium city –smalltown)C region(etc.)Needed region on lineoperationMain line 0.5km/unit 1 km/unit 3 km/unit Distance unlimitedAuto switch in Table 4 established 3.5 per one distributionline. Thus we made the auto switch standard as the basis oflocal section load and line length.Table 4. Switch standard as the basis of load and lengthManual CBMain lineAuto CBBranch point ofbranchA region 0.5km/1 unit 1.0km/1unit, section load: 1,600kW Over 5 spanB region 1.0km/1 unit 2.0km/1unit, section load: 2,000kW Over 10 spanC region 2.0km/1 unit 4.0km/1unit, section load: 2,000kW Over 30 spanWe made the standard of the auto-switch in line separation.And also made the standard of enlarge construction ofauto-switch. We then constructed a 6.5’ auto-switch per localload. This made it possible to detect fault section quickly andto swift transfer to normal section.3.5 Remote auto-switch control using PDA (personal digitalassistant)By using PDA remote control, we were able to increaseoperating efficiency and shortened the fault recovery time. Asa result, we were awarded the Electric-Energy Award inSeptember 2003. Operating PC in offices can control the PDAon the spot. If there is work during the night with one groupcomposed of only two workers, there is no one who canoperate system. So, the remote control can be executed byusing a PDA.3.6 New Distribution Information System-DistributionAutomation System (NDIS-DAS)NDIS-DAS connection system of distribution equipment wasdeveloped as follows:- By developing the system to connect the NDIS data toDAS, we can operate the system to reinforce the ability.- NDIS-DAS was connected to the T/F operation onbetween My 2002 and May 2003 (distribution office,Sale SI team, KEPRI and KEPCO )- NDIS-DAS connection is completed on June 2003. Theconnection principles of the DAS data for accepting thechanging equipment data from NDIS were modified.

Connection data was DAS operating data - circuitbreaker, the sort of wire, the thickness of wire and thedata of customer etc.- NDIS-DAS connection system operating was completeon November 2003. It recognizes electricity failureareas from DAS and identifies customers experiencingelectricity failure from NDIS and transfers it tocall-center.- Identifying customers experiencing electricity failureusing the interconnection of system can guide thecustomer more quickly and effectively.3.7 Accomplishments of distribution system operationThe time of black out was 12.38 (min/house/year) comparedto expected target. It was reduced by 14.2% compared to 7.3%last year. The fault-number of high voltage was a 1,137(times/year) in comparison to expected target. It was reducedby 23.2% compared to 9.0% last year. The maintenance ofnormal voltage represents 99.9% for goal 100%. This is theworld's best record.3.8 Power Quality Monitoring System (PQMS)One of functions of PQMS (Power Quality MonitoringSystem) is to ensure that High Technologic Detecting Systemmanages the black out, voltage frequency, harmonics, instantvoltage regulation, the electric waveform etc. caused by usinghigh-tech-electronic equipment. Operation and management ofPQMS can be summarized as follows:- In July 2003, the function of PQMS (Power QualityMonitoring System). We bring PQM-machinery (‘60)and measured some cases.- In October 2003, we obtained some data to establish thestandard for electric quality management.- There were established for efficiently managing aharmonics flowing in distribution system.- They were established to the study and execute thetolerance standard of a harmonics in distribution systemand a management standard. ('September 2002 ~'August 2004)areas, it will be difficult to solve these problems.- The distribution lines have so far been composed mostlyof radial systems, with the exception of one large city andmajor facilities.- The large city areas and those regions where concentratethere is concentration of buildings will be installed withunderground cables and the connecting devices (forexamples, transformer, circuit breaker, etc) will be appearon the outside in such a manner that is blends in with thesurrounding environment.- Dangerous side effects such as explosion, high voltageexposure will also be considered.In many parts, the control devices such as remote controllershould not be overuse for the case where it may reducesupplying reliability. And this is closely related with theformation of industrial sectors and factories. Lastly, withrespect to line composition, city atmosphere will be taken intoconsideration so that it blends well with the surroundingenvironment and consequently gain public acceptance.AcknowledgementsThis work was supported by EESRI, which is funded byMOCIE (Ministry of commerce, industry and energy). Theauthors are grateful to KEPCO, KPX and KEPRI forproviding relevant data required for conducting the powersystem analysis.References[1] KEPCO, "Distribution line map", 2003.07[2] KEPCO, "A study on establishing the new distribution systemconfiguration for high reliable & best quality services in 21 stcentury", 2003.09.[3] KEPCO, http://cis.kepco.co.kr/cis/cyber_spot /map[4] KEMCO, http://www.kemco.or.kr/english_new4 ConclusionsThis paper discussed the distribution line route, and presentedthe current status, and proposes future plans for thedistribution line for each respective area of South Koreadistribution line. In addition, the prospect about aboard whichwill be directed toward a future plans of distribution system inSouth Korea was attached as follows:- Most of the distribution lines have been constructed inline with both sides of streets along with state road andlocal roads. This arrangement can makes it easy for itsrestoration and extension by car.- As the geographical characteristics of each region inSouth Korea are complex with mixtures of mountainous