Optimal Analysis of Grounding System Design for Distribution Substation

Transcription

1 World Acdemy of cience, ngineering nd Technology Interntionl Journl of nergy nd Power ngineering Optiml Anlysis of rounding ystem Design for Distribution ubsttion T. Lnthrthong, N. Rugthichroencheep, A. Phyomhom Interntionl cience Index, nergy nd Power ngineering wset.org/publiction/ Abstrct This pper presents the electricl effect of two neighboring distribution substtion during the construction phse. The size of uxiliry grounding grid hve n effect on entire grounding system. The bigger the size of uxiliry grounding grid, the lower the PR nd mximum voltge, with the exception tht when the two grids re unconnected, i.e. the bigger the size of uxiliry grounding grid, the higher the mximum voltge. The results in this pper could be served s design guideline of grounding system, nd perhps remedy of some troublesome grounding grids in power distribution s system. Modeling nd simultion is crried out on the urrent Distribution lectromgnetic interference rounding nd oil structure (D) progrm. The simultion results exhibit the design nd nlysis of power system grounding nd perhps could be set s stndrd in grounding system design nd modifiction in distribution substtions. Keywords rounding ystem, Touch Voltge, tep Voltge, fety riteri. I. INTRODUTION HI pper focuses on grounding grid performnce during Tconstruction phse of new permnent distribution substtion in order to renovte existing one, while the other substtion hs not yet been removed. During the time of two ground grids left disconnected, the effect of uxiliry grounding system (de-energized electricl power site s) to the min sttion which remins energized cnnot be ignored. Becuse it will help crete high ground potentil rise (PR), especilly, the boundry wveform is very steep between the ground grids. For sfety purpose, ground grid design for the sfety of personl working round the vicinity of substtion construction site should be ensured. fety nd voltge re nlyzed with reference to sfety criteri bsed on body weight defined in I td systems [1], [2]. II. INIFIANT FATOR A. rth Resistivity Typicl rnges of resistivity for vrious soils nd should be used only for comprison purpose s show in Tble I. Although hve severl method for mesuring but the mostly Thong Lngthrthong is with the Deprtment of lectricl ngineering, Fculty of ngineering, Rjmngl University of Technology Phr Nkhon, Bngkok, Thilnd (e-mil: thong.l@rmutp.c.th). Nttchote Rugthichroencheep is with the Deprtment of lectricl ngineering, Fculty of ngineering, Rjmngl University of Technology Phr Nkhon, Bngkok, 10800, Thilnd (phone: ext. 150; fx: ext. 151; e-mil: e-mil: nttchote.r@rmutp.c.th). Att Phyomhom is with the Power ystem Plnning Deprtment, Metropolitn lectricity Authority (MA), Bngkok, 1192, Thilnd (phone: ; fx: ; e-mil: ttp@me.or.th). ccurte nd used is four point method or Wenner rrngement. Wenner rrngement is s shown in Fig. 1. Four electrodes re buried in eqully spce t point 1, 2, P1, nd P2. TABL I RAN OF ARTH RITIVITY Type of rth Averge Resistivity (Ω.m) Wet Orgnic oil 10 Moist oil 100 Dry oil 1000 Bed Rock I 1 P1 P2 2 V 1 P1 P2 2 Fig. 1 Wenner rrngement The resistnce R in ohm determine by V/I. Where I is current pss between two outer electrodes nd V is voltge between two inner electrodes [2]-[5]. B. round Potentil Rise (PR) The PR is equl to the product of the sttion ground grid impednce nd tht portion of the totl fult current tht flows through it [6].. fety riteri The sfety of person depends on preventing the criticl mount of shock energy. The sfety criteri re very importnt vlue. It should be first thing for clculte to specific sfety level, then the mximum nd voltge re clculted to compre with the sfety criteri to define it is sfe or unsfe [2]-[4]. D. Mximum Touch nd tep Voltge tep voltge is defined s the voltge different between distnt of 1 m with the feet without contcting [2]. Touch voltge is defined s the voltge different between ground potentil rise nd the surfce potentil t the point person is stnding while t the sme time hving hnd in contct with grounded structure [4], [7]. I b Interntionl cholrly nd cientific Reserch & Innovtion 8(8)

2 World Acdemy of cience, ngineering nd Technology Interntionl Journl of nergy nd Power ngineering Interntionl cience Index, nergy nd Power ngineering wset.org/publiction/ tep voltge nd voltge re used to determine sfety of the design. If it ws secured both of voltge should not exceed the limit [4]. III. ALULATIN PRODUR [2], [8]-[10] A. rth Resistivity The resistivity in the terms of the length units in which nd b re mesured is 4πR ρ = b + b is pprent resistivity of the soil Ω m R is resistnce b is depth of the electrodes m is distnce between two djcent electrodes m If b is smll compred to (1) cn be reduced to (2). (1) 2R (2) Two-lyer soil model is shown in Fig. 2. The soil resistivity cn be computed by using Wenner method. The formuls re shown in (3) nd (4). h 1 Top lyer 2 Bottom lyer Fig. 2 Two-lyer soil n n K K i1 h h n n 2 1 K is top lyer resistivity Ω m 2 is bottom lyer resistivity Ω m h is top lyer height m K is reflection coefficient B. round Potentil Rise round potentil rise is determined from (5) (3) (4) PR = I R (5) g I mximum rms current flowing between is ground grid nd erth (A) Rg is resistnce of grounding system. fety riteri tep voltge criteri is determined from (6) k t imilrly voltge criteri cn be obtined from (7) nd (8) h 0.09 is voltge (V) is voltge (V) is surfce lyer derting fctor is surfce mteril resistivity Ω m k is for 50 kg body weight for 70 kg body weight t is durtion of shock current (s) h is the thickness of the surfce mteril (m) is voltge (V) is voltge (V) is surfce lyer derting fctor If no protective surfce lyer is used, then 1 D. Mximum Touch nd tep Voltge The mximum voltge within mesh of ground grid is clculted by (9). m k t (6) (7) (8) K K I L (9) m i m M is mesh voltge (v) K m is pprent resistivity of the soil (Ω.m) is mesh fctor defined for n prllel conductors Interntionl cholrly nd cientific Reserch & Innovtion 8(8)

3 World Acdemy of cience, ngineering nd Technology Interntionl Journl of nergy nd Power ngineering Interntionl cience Index, nergy nd Power ngineering wset.org/publiction/ is corrective fctor for current irregulrity is effective length for mesh voltge (m) tep for design shown in Fig. 3. [2]. DnL,,, L T A, 3 I, t, d 0, c DnL,,, L, h T R, L, L g R I, t f I R < m, s, Km, Ks, Ki, Kii, Kh m s Fig. 3 tep for design procedure The voltge is determine from (10) K i L M K Ki I (10) = L is voltge (v) K is fctor defined for n prllel conductors c is effective length for voltge (m) IV. A TUDY izing of smll () medium (M) nd lrge (L) re 15x15 m 2, 30x30 m 2 nd 45x45 m 2 respectively shown in Fig. 4. There re three cses those re grid M-L M-M, nd M-, ll of 3 cses hve distnce between grid (d) 5 m. rid on the left is exist distribution substtion, grid on the right is uxiliry distribution substtion. Detils of constrints tht use for simultion re shown in Tble II. The results re crried out by D s shown in Tble III nd Fig rth Resistivity TABL II DTAIL OF ONTRAINT UIN FOR IMULATION 10 Ω m Depth of rid 0.5 m ize of onductor 95 mm 2 ompression Rtio 1 Fult urrent 25 ka Rod Height nd Dimeter 3 m nd 5/8 inches TABL III RULT FROM A TUDY Type PR (V) Touch tep Min Aux (V) (V) M-L 3, , , M-M 3, , , M- 3, , , Fig. 4 Two neighbouring distribution substtion is unconnected The ground grid constnt is medium (M) 30x30 m 2 nd then vry the size of the ground grid by side tht does not disptch power is clled uxiliry grounding system. It is found tht when the size of the uxiliry grounding system is lrge, Therefore PR of the min ground grid nd uxiliry grounding system of miniml size. Type M-L is the mximum voltge minimum, is equl to 2,014 V, nd if the uxiliry grounding system size is medium (M) nd smll () is the vlue of the mximum voltge is equl to 2,076. V nd 2,526 v, respectively, but for the vlue of the mximum voltge is reversed. Type M- is the lowest vlue of the mximum voltge is 383 V. Interntionl cholrly nd cientific Reserch & Innovtion 8(8)

4 World Acdemy of cience, ngineering nd Technology Interntionl Journl of nergy nd Power ngineering 2-D voltge mgnitude of grid type M-L, M-M nd M- re shown in Figs. 5, 7 nd 9. The results show tht colors ornge nd red of type M- is re of voltge more thn other type. 2-D voltge mgnitude is shown in Figs. 6, 8 nd 10. The results show tht the mximum voltge which included by ornge nd red re on the edge of min ground grid. Fig.7 2-D voltge mgnitude for type M-M Interntionl cience Index, nergy nd Power ngineering wset.org/publiction/ Fig. 5 2-D voltge mgnitude for type M-L Fig. 6 2-D mgnitude for type M-L Fig. 8 2-D mgnitude for type M-M Fig. 9 2-D voltge mgnitude for type M- Interntionl cholrly nd cientific Reserch & Innovtion 8(8)

5 World Acdemy of cience, ngineering nd Technology Interntionl Journl of nergy nd Power ngineering [7] M. Mitolo, P.. utherlnd nd R. Ntrjn, ffects of High Fult urrents on round rid Design, I Trns. Industry Applictions, vol. 46, no. 3,My/June, 2010 [8] A. Puttrch, et.l., ubsttion grounding grid Anlysis with the Vrition of oil lyer depth Method, in Proc. I onf. Lusnne, Power Tech. pp , [9] H. M. Khodr, et. l., Design of grounding systems in substtions using mixed-integerliner progrmming formultion, lectric Power ystems Reserch, vol. 79, pp , [10] J. He, nd et.l., esonl influences on sfety of substtion grounding system, I Trns. on Power Delivery, vol. 18, no. 3, July Thong Lnthrthong received his M.ng in lectricl ngineering from Rjmngl University of Technology Thnyburi, Pthumthni, Thilnd in He is currently n ssistnt professor t the Deprtment of lectricl ngineering, Fculty of ngineering Rjmngl University of Technology Phr Nkon (RMUTP), Bngkok, Thilnd. His reserch interests include power system opertion, optimiztion technique, nd distributed genertion. Interntionl cience Index, nergy nd Power ngineering wset.org/publiction/ Fig D mgnitude for type M- V. ONLUION The simultion results exhibit the design nd nlysis of power system grounding nd perhps could be set s stndrd in grounding system design nd modifiction in distribution substtions. The results show tht sizing of the uxiliry distribution substtion grid is inversely proportionl to PR nd voltge. As shown in Tble III, when the size of the grid increses from M- to M-L, PR decreses by 5% nd voltge decreses by 20%. On the contrry, the voltge is proportionl to the size of the grid. This is becuse in this cse the compression rtio is 1. Incresing the grid size mkes the conductors lines more prllel thn the smller size. The smller the resistnce vlue, the better the current flows into the ground. AKNOWLDMNT The uthors would like to express his grtitude to Rjmngl University of Technology Phr Nkhon, Thilnd for support nd Mr. Boonserm Ainsuk for his technicl support. RFRN [1] A. Phyomhom, nd et.l., fety nlysis for grounding potentil rise of two neighbouring substtions: cse study of metropolitn electricity Authority s ystem. In Proce. 44th Interntionl ouncil on Lrge lectric ystems (IR), Pris, Frnce, August [2] I td , I guide for sfety in A substtion grounding, [3] ANI/I td , I uide for Mesuring rth Resistivity, round Impednce, nd rth urfce Potentils of round ystem, [4] A. Phyomhom, nd et.l., fety design plnning of ground grid for outdoor substtion in MA s power distribution system, in Proc. lectricl ngineering/lectronics omputer Telecom. nd Informtion Technology Interntionl onf.. pp , [5] P. A. Zotos, round grid design in lrge industril plnts, I Trns. Industry Applictions, vol. 24, no. 3, pp , My/June, [6] I td , I recommended prctice for determining the electric power sttion ground potentil rise nd induced voltge from power fult, Nttchote Rugthichroencheep (M 10) received his Ph.D. in lectricl ngineering from King Mongkut s University of Technology North Bngkok (KMUTNB), Thilnd in He is currently ssistnt professor t the Deprtment of lectricl ngineering, Fculty of ngineering Rjmngl University of Technology Phr Nkhon (RMUTP), Bngkok, Thilnd. His reserch interests include power system opertion, optimiztion technique, nd distributed genertion. Att Phyomhom (M 14) received his Ph.D. degree in the lectricl ngineering Deprtment from the King Mongkut s University of Technology North Bngkok (KMUTNB), Thilnd in He hs worked for Power ystem Plnning Deprtment of Metropolitn lectricity Authority (MA) Thilnd since He is responsible for power system plnning. His min reserch interests re power system plnning, sfety design of ground grid in substtion nd lightning performnce. Interntionl cholrly nd cientific Reserch & Innovtion 8(8)