Research on Voltage Level Configuration in Medium Voltage Network of New Area

Transcription

1 6-9 Aprl 2008 Nanjng Chna 1 Research on Voltage Level Confguraton n Medum Voltage Network of New Area Hong Lu, haoyun Ge, and Xueme Jang Abstract--For new areas wth hgh orentaton, hgh vacancy and rapd development, tradtonal power supply wth 10 kv cannot meet ther load demand; therefore, medum voltage dstrbuton system for new areas should adopt 20 kv that has been utlzed wdely abroad. To solve the problems of power system voltage level confguraton n most areas, ths paper analyzes frst the feasblty of 20 kv supply from the aspects of technology, equpment and management. Then comparson on economcal effcency between 10 kv and 20 kv supply plans for dfferent load denstes s provded wth the mnmum cost model. Relablty of dfferent supply plans s also analyzed wth classcal relablty theory. At last, t s concluded that the 20 kv power supply plan should be a prorty for new areas based on comprehensve comparsons on technology feasblty, relablty and economcal effcency of operaton. Index Terms--Local area networks, Power dstrbuton network, Power supples, Voltage level W I. INTRODUCTION ITH the rapd development of natonal economy, many new areas have been brought nto the natonal and local development strategy, thus the demand on electrc power n new areas ncreases contnuously as well. Therefore, nvestment on constructon and reconstructon of power system also ncreases on a large scale, whch brngs many opportuntes. However, hgh load densty as a result of rapd economc development and hgh load demand wll mpose more pressure on network structure and power supply relablty. At present, the tradtonal 10 kv power supply s appled by most medum voltage dstrbuton systems n Chna. At the same tme, 35 kv s utlzed to provde drectly supply to mportant and large customers. However, the defects of 10 kv supply plan has become so obvous that t cannot satsfy the load ncrease [1]-[3]. Consequently, there comes the bottleneck at supply to great clents wth 35 kv. As a result, t s necessary to consder hgher voltage level n new areas [4], [5]. Currently, 20 kv supply has become IEC standard for medum voltage dstrbuton system. It has also been natonal standard n many countres such as the Unted tate, Russa, Japan, France, Italy, Canada, German, Bulgara and Hungary, etc.[6], [7]. In 1996, the uzhou Industral Park frst utlzed 20 kv to supply power n Chna. 10 years operaton experence shows the feasblty of 20 kv as dstrbuton voltage level [8], [9]. Although the advantages of 20 kv dstrbuton system has been well-known, further analyss on ts technologcal and economcal effcency s necessary, because of such problems as hgh constructon costs, nsuffcent operaton experence and poor compatblty wth 10 kv areas due to mmature manufacture capablty of 20 kv electrc equpment. Ths paper conducts comprehensve studes on current voltage level confguraton to get problems n 10 kv voltage level. Based on the analyss of the 20 kv s advantage on technology and avalablty of equpment and management, several supply plans wth 10 kv and 20 kv are compared and studed n detal at dfferent load denstes wth the classcal relablty theory and mnmal cost model. It s concluded that power supply wth 20 kv s pror to that wth 10 kv fnally. II. CURRENT URBAN POWER YTEM A. Voltage arrangements and thers problems At present, power systems n Chna take 500 kv and 220 kv as hgh transmsson voltage level, 110 kv and 35 kv as hgh dstrbuton voltage level, 10 kv as medum voltage level. A fve-level system s wdely used as 500/220/110(35)/10/0.4 kv n power systems, whch causes serous repeated transformaton. And furthermore, t not only ncreases constructon nvestment and operaton mantenance cost, but also rases power loss and reduces relablty. The voltage level arrangement s analyzed as n Fg. 1. Hong Lu s wth the chool of Electrc Automaton Engneerng, Tanjn Unversty, Tanjn, Chna(e-mal: tjuluh@126.com). haoyun Ge s wth the chool of Electrc Automaton Engneerng, Tanjn Unversty, Tanjn, Chna(e-mal: syge@tju.edu.cn). Xueme Jang s wth TD Qush Electrcal Hgh technology Co. Ltd, Tanjn, Chna (e-mal: xueme_jang26@126.com). Fg. 1 Transformaton arrangement of actual power system trctly speakng, present medum voltage dstrbuton levels nclude 110 kv and 35 kv, and the latter manly /08/ 2008 DRPT

2 6-9 Aprl 2008 Nanjng Chna 2 provdes for some bg load customers. It s obvous that the arrangement has serous repeated transformaton. There are 110 kv and 35 kv n hgh voltage dstrbuton level, and there are 35 kv and 10 kv n medum voltage level. Generally the transformaton arrangement s not clear enough and ts standardzaton s poor. B. Man problems on current power system Although actual power system can ft prelmnary supply demand, there are stll some problems n operaton ncludng. (1) Low dstrbuton supply capablty and the rato of capacty to load; (2) Hgh power loss of medum and low voltage network; (3) Poor voltage qualty. The selecton of medum voltage level can drectly affect the relablty, power qualty and economcal effcency of power system. 10 kv as one of the medum voltage level s currently the key to lnk hgh voltage and low voltage dstrbuton systems therefore plays an mportant role n the development of power system. However, load denstes of most new areas wll be very hgh n the future. For example, uzhou Industral Park s load densty wll reach 50 MW/km2,and load densty of Bnha New Area of Tanjn wll exceed 100 MW/km2. Urban electrc power demand ncreases rapdly wth result of the development of the economy n new area, so the gap of 10 kv dstrbuton voltage level wll be gradually obvous on the economy and flexblty. III. APPLICATION OF 20 KV APPLIED IN NEW AREA The correct prncple of selectng dstrbuton voltage levels s that the voltage level s advanced and feasble on technology, and s economcal and logcal on operaton. In addton, t s taken nto account n a whole wth transmsson voltage levels, the dstrbuton condton n local area and the load densty and ncreasng speed forecast. Ths paper studes the 20 kv applcaton n new areas on the feasblty of technology, relablty of power supply and economy of operaton. Three arrangements, 220/110/10, 220/110/20 and 220/20 are analyzed respectvely and compared n dfferent load denstes on the calculaton of the relablty of power supply and economy of operaton. The substaton szes selected by the paper are showed as n Table I. TABLE I THE UBTATION IZE OF EVERY VOLTAGE LEVEL ARRANGEMENT ource of medum voltage Voltage level The upper substaton Project dstrbuton system arrangement Number (kv) pecfcaton ze pecfcaton ze (kv) (MW) (kv) (MW) 1 220/110/10 110/10 2*50/3*50 220/110/10 3* /110/20 110/20 2*63/3*63 220/110/20 3* /20 220/20 2*90/3* A. Technologcal analyss 1. The advantages It s known through theoretcal analyss that the 20 kv has the advantages of the ncrease of transmsson power and decrease of power loss, so the man technologcal advantages of 20 kv nclude several aspects as follows on the technologcal parameter [10], [11]. (1) Decrease voltage loss: after the voltage s rased from 10 kv to 20 kv, the voltage drop can decrease 75% f the load s unaltered and t can decrease 50% f the load s doubled; (2) Enhance power transfer capablty of the lne: the transmsson capablty of 20 kv s double of that of 10 kv; (3) Increase supply radus of medum voltage network: the supply radus wll be doubled when the voltage s rased from 10 kv to 20 kv; (4) Reduce power loss: power loss wll be reduced by 75% as load remans the same after the voltage level s rased; (5) ave nonferrous metal: the nonferrous metal expense wll be reduced by 50% when the power transfer capablty s unaltered after the voltage level s rased. In addton, the 20 kv dstrbuton can also decrease the transformer loss wth no-load and load. Theoretcally 20 kv dstrbuton system should be appled n new area from the above analyss. 2. Feasblty analyss From the technologcal parameters, 20 kv as voltage level on dstrbuton system has many advantages on the economcal aspects. Moreover, ths paper analyzes the feasblty n technology and management of 20 kv dstrbuton system. (1) uffcent manufacture capablty and reasonable cost are avalable for 20 kv electrcal equpment. 10 kv and 20 kv are medum voltage dstrbuton levels, so the desgn and manufacture technology of ther equpment are sar. Wth the 20 kv applcaton n uzhou Industral Park, some manufacturers already have certan capabltes to produce many equpments, such as dstrbuton transformers, power cables, swtches, nsulators, etc., whch are exported to some countres n outheast Asa, although ther costs are 3%~5% hgher than those of 10 kv. (2) The power utltes have adequate experence on 20 kv operaton. ome areas such as uzhou Industral Park are suppled by 20 kv, whose experence on operaton and management can be used as reference by other new areas. Furthermore, such experence wll be gradually accumulated wth the ncrease of 20 kv power systems. B. Relablty analyss Relablty s a basc ndex that s correlatve to supply qualty. The man ndces of relablty evaluaton are outage frequency, duraton of every outage, and customers cost on self-supply durng outages, etc.. These ndces are related to all knds of factors, such as equpment relablty, length and load of each lne, grd structure, level of dstrbuton automaton, the form of load curve and load transfer ablty. (1) Basc model One of the assumptons of classc relablty evaluaton methods s that all components are n seres and falure of each component s ndependent. Base on the assumpton, ths paper calculates three ndces, average fault rate λ, average

3 6-9 Aprl 2008 Nanjng Chna 3 nterrupton tme r and average nterrupton tme per year U as n (1), (2) and (3). λ = λ (1) U r = λ r (2) U = = λ λ r λ In whch, λ s average fault rate of a gven element and r s average outage tme of element. The unts of λ r U are tmes per year, hours per outage and hours per year, respectvely. Average ervce Avalablty Index (AAI), ystem Average Interrupton Frequency Index (AIFI) and ystem Average Interrupton Duraton Index (AIDI) are appled to evaluate the relablty to represent the severty of system nterrupton. consumer usng hours N 8760 UN AAI = = (4) consumer demand hours N 8760 consumer nterrupton tmes λ N AIFI = = (5) consumer quantty N summaton of consumer nterrupton duraton AIDI = consumer quantty UN (6) = N In above three equatons, N s the quantty of all consumers, N s the quantty of affected consumers that s relatve to average nterrupton tme U ; 8760 s the hours n one year. The fault rate of overhead lne and cable are a drect rato wth ther length. (2) Basc parameter selecton The basc parameters on the calculaton are shown n Table II. TABLE II BAIC PARAMETER OF RELIABILITY Equpment Dstrbuton transformer Fault rato of equpments Average repar tme (hours per tme) 0.006(tmes/unt*year) 1.98 Breaker (tmes/unt*year) 1.7 ecton swtch 0.13(tmes/unt*year) 3.7 Bus 0(tmes/unt*year) 0 overhead lne 0.12(tmes/km*year) 3.35 cable 0.17(tmes/km*year) 4.12 The nacton rato of breaker s 2.11%, and the swtch operaton tme on each fault s 1.5 hours. (3) Result analyss Ths paper calculates the relablty of the overhead and cable n dfferent load denstes (1.0, 2.0, 5.0, 10.0, 20.0, 50.0, 60.0; the dmenson s MW/km 2 ), whose result s showed as n (3) Fg. 2 and 3. The optmal secton has been chosen on every connecton mode. Relablty Fg. 2 The relablty of overhead lne of each project Relablty Load Densty(MW/km 2 ) Load Densty(MW/km 2 ) Fg. 3 The relablty of cable of each project It s concluded through above result fgures on the analyss of overhead and cable that, 1) The relablty of dstrbuton system wll be mproved wth the ncrease of load densty n the supply area. The reason s that the supply radus wll be decreased and the lne from substaton to load s shortened when load densty ncreases whereas the capablty of substaton remans unchanged. Because average fault rato s drectly proportonal to the length of the lne, the relablty of dstrbuton system can be mproved accordngly. 2) Under any load denstes, the relablty of 10 kv project s better than that of 20 kv, and moreover the 220/110/20 kv project s better than the 220/20 kv one. Otherwse, because the fault rato of overhead network s hgher than that of cable network, the relablty of overhead network s lower on the contrary. C. Economy analyss The basc method to estmate the economy of dstrbuton projects s to fnd the supply area of the substaton on dfferent load denstes n a certan substaton capablty and to calculate the mnmal cost on unt load of each project consderng grd structure of medum voltage connecton mode and hgh voltage substatons and lnes. (1) The model of mnmal cost The model s descrbed as that the optmal project s found by mnmzng the object functon of mnmal nvestment and operaton expense under the approxmate substaton and network and the gven dstrbutng load n plannng year. mn C = ZU + LZU + PZU + LHZU (7)

4 6-9 Aprl 2008 Nanjng Chna 4 The cost models of substaton, medum voltage lne, dstrbuton transformer and hgh voltage lne are showed as follows. ms ZU = Z U ms (8) LZU = LZ LU (9) mp PZU = PZ PU (10) LHZU = LHZ LHU (11) r 0 s dscount rate; ms s deprecaton lfe of substatons; s deprecaton lfe of lnes; mp s deprecaton lfe of dstrbuton transformers. To get more feasble project, the economy contrast wth the dstrbuton project apples mnmal cost on unt load that s showed as follows. mn C ZU + LZU + PZU + LHZU NF = = (12) P TABLE III THE COT PARAMETER OF THE EQUIPMENT DIMENION: MVA, KVA, TEN THOUAND YUAN/UNIT, TEN THOUAND YUAN/KM Voltage (kv) /10 Type ubstaton Lne ubstaton Lne Lne Dstrbuton transformer P Unt cost Capablty Remark Cost Model /17000 Indoors/outdoors /12500 Indoors/outdoors LGJ Double on a tower LGJ Double on a tower /4500 Indoors/outdoors /5500 Indoors/outdoors LGJ ngle on a tower YJV Cable 380 Tunnel YJV /160 Includes tuner JKLGYJ /33 Overhead nsulaton /10 On the tower / /45 Dstrbuton box / /150 Dstrbuton room Annotatons: substaton outdoors s used on the overhead network, whch on 110 kv and 220 kv supply electrc power wth overhead lnes; substaton ndoors s used on the cable network, whch on 110 kv and 220 kv supply electrc power wth cables. (2) Basc parameter selecton The cost selecton of substaton, medum voltage lne, dstrbuton transformer and hgh voltage lne assocated wth the project comparson s shown n Table III. In addton, the cost hours on maxmal load s 3400h and the electrc prce s 0.4 yuan/kwh; the deprecaton lfe of substaton, dstrbuton transformer, overhead and cable s 25 years, 25 years, 25 years and 30 years respectvely. The dscount rate s 0.1. cost on unt load (ten thousands yuan/mw ) Fg. 4 Mnmal cost on unt load of every project (overhead lne) cost on unt load (ten thousands yuan/mw ) load densty(mw/km 2 ) Fg. 5 Mnmal cost on unt load of every project (cable) load densty(mw/km 2 ) TABLE IV DETAILED CONTRAT WITH MINIMAL COT OF DIFFERENT PROJECT Lne types Overhead Cable Cost Load densty(mw/km 2 ) Projects sorts ubstaton Medum voltage lne Medum voltage dstrbuton transformer Hgh voltage equpment ummaton ubstaton Medum voltage lne Medum voltage dstrbuton transformer Hgh voltage equpment ummaton (3) Result analyss The paper calculates the economy of the overhead and cable n dfferent load densty (1.0, 2.0, 5.0, 10.0, 20.0, 50.0, 60.0; the dmenson s MW/km2), whose results are showed as n Fg. 4 and 5. The conclusons are as follows through the analyss on overhead and cable network.

5 6-9 Aprl 2008 Nanjng Chna 5 (1) It s obvous n Fg. 4 and 5 that the costs on unt load of all projects would decrease wth the ncrease of load densty of supply area. The supply radus wll be reduced wth the ncrease of load densty and the nvarant capablty of substaton, whch wll cause that the length of lne from the substaton to the load s shortened, and ts nvestment and cost on unt load decreased. (2) It s known from Table IV that the costs on unt load of hgh voltage substatons and lnes s optmal n 220/20 kv project because t has not the nvestment of substatons and lnes of 110 kv voltage level wth relatve to the 220/110/10(20) kv. At the same tme, the costs on unt load of medum voltage lnes and dstrbuton transformers n cable network are hgher than that n overhead network. In overhead networks, the 220/110/20 kv project s the best one of three projects and the 220/20 kv s the worst one f load densty s smaller than 10 MW/km 2. However f load densty s larger than 10 MW/km 2, the 220/20 kv project s optmum, whch can be better and better wth the ncrease of load densty. The 220/110/20 kv project s worse than the 220/20 kv one and better than the 220/110/10 kv one. In cable networks, the 220/20 kv project s best n three projects. Moreover, and the 220/110/10 kv one s worst of three projects on any load densty. The cost on unt load of the 220/110/20 kv project s better than that of 220/110/10 kv, and the advantage wll be decreased wth the ncreases of load densty. D. Result of the argumentaton It s concluded as follows on the foundaton of above ntegrated analyss on technology and economy of dstrbuton system. (1) upply relablty The relablty of every project on the overhead and cable network wll reach 99.9% beyond vew of plan nterrupton, whch can ft the demand of electrc power supply. In three projects, the relablty of 220/110/10 kv s the hghest one and that of 220/20 kv s the lowest one. (2) Operaton economy Load densty wll exceed 10 MW/km2 n the future, and moreover the cable should be utlzed as transmsson and dstrbuton lne n urban power system of most areas. Therefore the economy of 220/20 kv s the best one n three projects. It s summed up that the 220/20 kv and 220/110/20 kv projects are better than that of 220/110/10 kv on economy under the precondton that the supply qualty of power system s ensured, and therefore t s recommended that 20 kv voltage level be appled on medum voltage dstrbuton system. IV. CONCLUION From the technologcal vew, the relablty of 20 kv voltage level s lower than the 10 kv plans on medum voltage dstrbuton system, but t can also satsfy the demand of supply qualty and reduce many lne corrdors to solve the dffculty of channel selecton, and ts operaton and mantenance s correspondngly smple. Because the prces of 20 kv equpments are hgher 1.1~1.2 tmes than that of 10 kv, but the capabltes of 20 kv equpments s double than that of 10 kv, so the 20 kv project s cost-effectve. From the economcal vew, the 220/20 kv project has not the 110 kv voltage level wth relatve to the 220/110/10(20) kv, whch make mnmal cost per load wdely dfferent. But for the area wth low load densty, the 220/110/20 kv project s better than the 220/20 kv one. o t can be concluded that the 20 kv project have defnte advantages than 10 kv. As a result, the 20 kv s recommended as medum voltage dstrbuton level on new area. The 220/20 kv s selected as voltage arrangements on the area wth hgh load densty, and the 220/110/20 s chosen as voltage arrangements on the low load area. V. ACKNOWLEDGMENT The authors gratefully acknowledge the contrbutons of Dongl Ja, We Ja and Zhu Chen for ther work on the orgnal verson of ths document. VI. REFERENCE [1] Jang Xangsheng, An nvestgaton on voltage class for urban dstrbuton network,power system technology, vol. 3, pp ,45, Feb [2] Qan yun, Wang Yang, Dscusson on necessty of developng 20kV voltage grade n dstrbuton network, Anhu electrc power, vol. 3, pp , Mar [3] un Xhua, Fan Xangrong, Reconstructon of urban dstrbuton network should select 20kV voltage grade frstly, Zhejang electrc power, vol. 6, pp. 6-10, Jun.1996 [4] Zeng Zenggong, electon of the voltage grade of the electrc network, handong electrc power technology, vol. 3, pp , Mar [5] Fan Mngtan, Zhang Zupng, Lu ge, Ratonal schemng of voltage level n urban electrc networks, Power system technology, vol. 10, pp , Oct [6] Yu Jao, Dscusson on voltage grade n md-voltage dstrbuton grd, Helongjang electrc power, vol. 4, pp , Apr [7] Guo Rca, Yuan Zhaoxang, L Baojn, A survey on typcal desgn of substatons n France and Korea and relevant suggeston to power network engneerng n Chna, Power system technology, vol. 6, pp , Jun [8] Jang Xangsheng, Wang Hongye, Yao Guopng, Practces on 20kV voltage level n uzhou ndustral park, Dstrbuton & Utlzaton, vol. 12 pp. 1-7, Dec [9] Jang Xangsheng, Qn Feng, Hu Dajan, Extenson of power supply area wth dstrbuton voltage level 20kV, Dstrbuton & Utlzaton, vol. 3, pp , Mar [10] Lang hu e, Reasonng to apply dstrbuton voltage level 20kV, Proceedngs of the LEE, vol. 1, pp , 1997 [11] Yu Ronghua, chemng and optmzaton of dstrbuton voltage level, cence & Technology Informaton, vol. 25, pp. 31, Apr VII. BIOGRAPHIE Hong Lu was born n Tanjn on November 7, He receved master degrees from chool of electrc automaton engneerng n Tanjn Unversty n 2005 and now s studyng for Ph.D. at the same place. Hs major s urban power system programmng and decson support theory on power system. And he have employed hmself n the programmng on urban power system at the TD Qush Electrcal Power Hgh Technology Co. Ltd and completed many projects of actve and reactve power programmng of regonal power system snce Feb

6 6-9 Aprl 2008 Nanjng Chna 6 haoyun Ge was born n Handan on August 10, He receved master degrees from chool of electrc automaton engneerng n Tanjn Unversty and acqured hs Ph.D. from Hong Kong Unversty. Hs major s urban power system programmng and automaton of dstrbuton system. And moreover he s a professor n Department of power system and ts automaton n Tanjn Unversty and has publshed more than 20 papers n IEEE. In addton, he has accomplshed two Natural centfc Funds of Chna and receved the second prze of the Natural centfc and Technologcal Progress. And he s also the general manager of TD Qush Electrcal Power Hgh Technology Co. Ltd whose man busness s urban power system programmng and ts relevant researches. Xueme Jang was born n Tanjn on December 10, he receved master degrees from chool of electrc automaton engneerng n Tanjn Unversty n 2005 and now s workng n TD Qush Electrcal Power Hgh Technology Co. Ltd. Her major s urban power system programmng and automaton of dstrbuton system. And she have employed hmself n theoretcal research and practcal consultaton on programmng of urban power system n above company.