DISTRIBUTION VOLTAGE MONITORING AND CONTROL UTILIZING SMART METERS

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1 4 th Iteratoal Coferece o Electrcty Dstrbuto Glasgow, -5 Jue 07 DISTRIBUTION VOLTAGE MONITORING AND CONTROL UTILIZING SMART METERS Yoshhto. KINOSHITA Kazuor. IWABUCHI Yasuyuk. MIYAZAKI Toshba Japa Toshba Japa Toshba Japa yoshhto.koshta@toshba.co.jp kazuor.wabuch@toshba.co.jp yasuyuk.myazak@toshba.co.jp ABSTRACT Covetoal dstrbuto voltage cotrol system does ot motor ad cotrol wde area of low voltage (LV). I the case that LV ear the ed of the dstrbuto le s deeply dropped due to heavy load, there s the potetal that LV surpasses the upper or lower lmt of dstrbuto voltage. To regulate LV wth the lmts, the voltage cotrol s requred to mprove ts performace. O the other had, smart meter whch s devce reportg the voltage ad eergy cosumpto at each customer s stalled varous regos. To regulate LV wth the voltage lmts, the cotrol whch utlzes LV measured by smart meters s proposed ths paper. As a problem about the proposed cotrol, the cotrol requres to select meters for motorg ad cotrollg the voltages all LV etworks. Therefore, the selecto method of smart meters ad voltage cotrol utlzg smart meters s studed, ad the performace of the voltage cotrol s evaluated. INTRODUCTION There s a problem that LV ear the ed of the dstrbuto le s deeply dropped due to heavy load. Covetoal cotrol wthout measurg the LV drop ear the ed of the le s ot able to resolve the LV problem. O the other had, smart meter whch s devce reportg voltage ad eergy cosumpto at each customer s stalled varous regos. I ths paper, to resolve the LV problem, the voltage cotrol cosderg LV measured by smart meters s studed. As a problem about the proposed cotrol, the samplg tme to collect the measured voltages from meters depeds o the umber of the meters appled to the cotrol. To shorte the samplg tme, several tes of represetatve meters for the cotrol are selected uder costrats to eable the cotrol to observe all LV codtos. To select the meters, a method to select the meters havg measured the hghest voltage or the lowest voltage at the ed of etwork s proposed []. However, the meters do ot always measure the hghest or the lowest voltage the meters ad the voltage cotrol does ot measure the voltage profle of the other meters. Hece, ths voltage cotrol mght ot regulate the all voltages all LV etworks ad be ot able to optmze the outputs of voltage cotrollers such as trasformer ad statc codeser. Thus, ths study, several tes of meters are selected as represetatve meters, ad all voltages of the meters are estmated by the measured voltages of the represetatve meters. I addto, the voltage cotrol regulates all estmated voltages. I a smulato, the performace of the voltage cotrol s evaluated. VOLTAGE CONTROL UTILIZING SMART METERS A Cocept of selecto method of smart meters ad voltage cotrol Voltage treds measured by the earby meters have smlar voltage characterstcs because mpedaces betwee the meters are low due to short dstace. Therefore, the represetatve meters are selected from the meters wth smlar voltage characterstcs. These represetatve meters eable to estmate the all voltage LV etworks wthout the others by smlar characterstcs. Here, Process of the meter selecto ad the voltage cotrol s descrbed as follows ad the cotets of each process are descrbed from ext secto detal. Process of meter selecto method (Fgure ) (Ths process s executed about oce a moth.) Step S: Prevous voltages measured by all meters are collected a database. Step S: The tme seres of LV the database are categorzed o the bass of smlarty of wave form. Step S3: Represetatve meters for the voltage cotrol are selected from each category step S. Step S4: To estmate the voltages of the other meters from the voltages of the represetatve meters, coeffcets of voltage relatoal equatos betwee the represetatve meter ad the others are calculated. Voltage cotrol utlzg represetatve meters (Ths cotrol s executed at all tmes.) Step V: The voltages of the represetatve meters are oly collected. Step V: The voltages of the other meters are estmated by usg the voltage equatos from the voltages of the represetatve meters. Step V3: The voltage cotrol regulates the estmated voltage to desg rage ad mmzes the output devatos of the voltage cotrollers. Step S3 Step S Represetatve Step S V α V R +β Represetatve Others Step S4 Tme Fgure. Cocept of selecto method for smart meter Voltage CIRED 07 /5

2 4 th Iteratoal Coferece o Electrcty Dstrbuto Glasgow, -5 Jue 07 Categorzg method based o smlarty of voltage wave form (step S~S meter selecto) As a categorzg method based o smlarty of the voltage wave form, the voltage smlarty betwee meters s evaluated by the correlato defed (). The voltages of the meters are categorzed by herarchcal clusterg o the bass of the correlato. Image of the herarchcal clusterg s show Fgure. Ths clusterg method categorzes herarchcal. I the hgher herarchy, meters wth smlar wave form the lower herarchy are categorzed to the same category. Here, because the represetatve meters are selected each category, the umber of represetatve meters s equal to the umber of categores. Therefore, the umber of the categores s desged to meet costras of the cotrol system. Rj )( v jk j ) ) ( v jk j ),j : Meter umber (~p) : Number of tme seres data v : Voltage data of meter at v : Mea value of v Low correlato Hgh correlato Hgher Herarchy Lower Meters wth smlar wave form are categorzed. Fgure. Image of herarchcal clusterg Meter selecto method by dsturbace evaluato based o factor aalyss (step S3 meter selecto) As show Fgure 3, the voltage tred measured by smart meter cosst of the commo voltage treds f betwee some meters ad the uque voltage tred e caused by local demad fluctuato each cosumer. To estmate LV of the other meters by represetatve meter the voltage cotrol, desrable voltage characterstcs of the represetatve meters are ot to clude the uque voltage tred as a dsturbace but the commo voltage treds. To select the meters wth the desrable characterstcs as represetatve meter, factor aalyss s appled. Here, a defto of the voltage s descrbed (3) ormalzed by (). As assumptos, f ad e meet the costrat codtos (4). V Meter umber Number of categores: v ) k Number of categores:3 () () Meter voltage [ ] Assumptos of e ad f Uder the costrat codtos (4), correlato of the voltages (3) s show (5). I (5), the dagoal elemets σ +Σa k are equal to. I addto, the correlato (5) s equal to the correlato calculated by actual value of tme seres voltage data. Therefore, a k ad σ are calculated from these codtos. The σ s the varace of the e, ad the comparso of σ betwee meters eables to evaluate the magtude of the uque voltage tred. To select the meter wth desrable voltage characterstcs as represetatve meter, the voltages each category are appled the factor aalyss ad σ of the uque voltage tred are calculated. The cotrol system selects the meter whose 3σ s less tha a desg value each category as represetatve meter. I case that there are some meters havg 3σ less tha the desg value, a meter whose voltage frequetly reaches mmum voltage s selected. m m σ + a k k a k ka pk R m m a k pkak σ p a k pk + T [ Λ Λp ] [ Λ Λp ] + dag[ σ σ p ] The commo voltage treds f betwee some meters Voltage tred f medum voltage dstrbuto etwork Voltage tred f MV/LV trasformer Voltage tred f3 LV le V Λ f + e (3) V v v : Tme seres voltage data of meter T f [ f fm ], fm [ fm fm] : Commo voltage treds m s the umber of the treds Λ [ a am ] : Coeffcets of f e [ e e ] : Uque voltage tred ek fmk 0, eke jk 0, j fmk 0, fmk, ek 0, Uque voltage tred e caused by local demad fluctuatos each cosumer ek σ Fgure 3. Defto of voltage treds measured by meters (4) (5) CIRED 07 /5

3 4 th Iteratoal Coferece o Electrcty Dstrbuto Glasgow, -5 Jue 07 Voltage relatoal equatos betwee the represetatve meter ad the others (step S4 meter selecto) The represetatve meters are selected from categores cossted of meters wth smlar voltage tred. From ths voltage smlarty, the voltage relatos betwee represetatve meter ad the other meters same category are approxmated as (6). I (6), α ad β s calculated by regresso aalyss. Vest α VR + β (6) V R : Voltage of represetatve meter V est : Estmated voltage, α, β :Coeffcets I operatg the voltage cotrol, the voltages are estmated by substtutg the voltage of the represetatve meter the voltage relatoal equatos. However, the voltage estmato cludes estmato error due to approxmato (6). To cosder the error, probablty dstrbuto ƒ(e est ) of the estmato error E est each meter are calculated as Fgure 4. I Fgure 4, τ M s rage whch cludes probablty of the estmato error from EL est to EH est. By settg τ M to compesate the estmato error voltage cotrol, EL est ad EH est are derved as margs for voltage cotrol ext secto. Fgure 4. Probablty dstrbuto of estmato error E est Voltage cotrol Voltage sestvty of meters to voltage cotroller I the prevous secto, the represetatve meters are selected ad the voltage codtos all etworks are estmated from the voltages of represetatve meters. I order to regulate these voltages, the cotrol system has to determe whch voltage cotrollers are able to regulate the estmated voltages effcetly. I partcular, there s a case that etwork cofgurato s uclear. Hece, voltage sestvty of the estmated voltages to the cotrollers s calculated uder uclear etwork cofgurato, ad the sestvty s used the voltage cotrol for determato of the voltage cotrollers. The method to calculate the voltage sestvty s show Fgure 5. From Fgure 5, the sestvty s calculated by voltage dervato of the meter to the output of the voltage cotroller at operato of the voltage cotroller. Voltage of smart meter Output of voltage cotroller u V Tme dv du Fgure 5. Evaluato method of voltage sestvty Measured V Actual V The dervato of voltage before ad after operato of voltage cotroller Optmal outputs of voltage cotrollers (step V~ V3 Voltage cotrol) The cotrol outputs of the voltage cotrol are adjusted whe the estmated voltages of the meters surpass desg rage. The, ts cotrol regulates LV to mmze ΔV ad Δu. Here, ΔV are the dffereces betwee the estmated voltages ad referece voltage. Δu are the chagg values of the cotrol output such as statc codeser ad trasformer. To evaluate ΔV ad Δu, costrat codtos wth regard to the desg rage of V ad u are defed (7). I addto, objectve fucto s defed (8). The voltage cotrol calculates the cotrol output u to meet (7) ad to mmze (8). Costrat codtos Vm < Vest + DΔu EL est Vmax > Vest + DΔu + EH (7) est um < u + Δu < umax Objectve fucto p l mmze ΔV k + η Δu k (8) ΔV Vref ( Vest + DΔu) Where, Vest u d dl (9) V est, u, D Vest p ul dp dlp V est : Estmated voltages (6) V ref : Refereces of voltages V max : Upper lmts of voltages V m : Lower lmts of voltages u : Cotrol output of voltage cotroller D : Voltage sestvty for voltage cotroller(δvdδu) EH est, EL est : Marg for compesato of estmato error Fgure 4 η :Weghtg coeffcet Wth regard to mmzato for the objectve fucto (8) uder the costrat codtos (7), these equatos are lear equalty. To resolve quckly the mmum cotrol outputs u for the lear equalty, lear programmg s appled. CIRED 07 3/5

4 4 th Iteratoal Coferece o Electrcty Dstrbuto Glasgow, -5 Jue 07 SIMULATION VERIFICATION Smulato codtos Dstrbuto etwork I order to evaluate performace of the voltage cotrol, bechmark model for medum voltage (MV) dstrbuto etwork [3] Fgure 6(a) ad that for LV dstrbuto etworks [4] Fgure 6(b) are appled. As a dstrbuto etwork cofgurato, the MV etwork, ts capactaces are gored, ad ts each ode s coected the low voltage dstrbuto etwork. I addto, each load MV ode s dvded to the coected LV odes. The, to smulate dfferet characterstcs each LV cosumer, load wth radomly fluctuato s added to each LV cosumer. I ths smulato, there are about a thousad cosumers. As a example, voltages of meters are show Fgure 7. N04 N N05 N0 N09 Dstrbuto trasformer N0 N0 N03 (a)medum voltage(mv) dstrbuto etwork Voltage TR N08 N07 N06 L0: Sgle resdetal cosumer L0: Group of 4 resdeces Fgure 6. Smulato model L05: Apartmet buldg (b)low voltage(lv) dstrbuto etwork Fgure 7. Low voltages of smart meters Table. Specfcato of smart meter [5] Rated 40V 00A 60Hz Accuracy 0.5% Measurable Itegral power cosumpto tems Istataeous voltage Istataeous curret etc. Samplg tme 5, 30, 60m L03: Apartmet buldg L04: Sgle resdetal cosumer Smart meter The specfcato of smart meter s show Table. It s assumed to eable to measure actve power ad stataeous voltage every 5~60 mutes. I the proposed method, the cotrol system corrects the voltages of the represetatve meters at all tme ad the voltages of the other meters low frequetly. Thus, the samplg tme to correct the voltage of represetatve meters s set to 5m. Smulato results Selecto of represetatve meters The meter selecto method s appled to the voltage data Fgure 7. The result of categorzg s show Fgure 8. From Fgure 8, t s cofrmed that the meters are categorzed by smlarty of the voltage wave form. Here, the represetatve meters are selected from each category by dsturbace evaluato based o factor aalyss. For example, the result of dsturbace evaluato for category Fgure 8 s show Fgure 9. I Fgure 9, the varace σ of the uque voltage tred each meter s calculated. The cotrol system select the meters whose 3σ s less tha a desg value each category. I addto, because there are the meters havg 3σ less tha the desg values, a meter whose voltage frequetly reaches mmum voltage s selected fally. I Fgure 9, the meter of umber s selected. Voltage estmato ad voltage cotrol For the voltage cotrol, Fgure 6, the tap of dstrbuto trasformer (TR) ad reactve power of statc codeser (SC) set o the MV odes N06 ad N are utlzed. The results of the voltage estmato ad cotrol are descrbed Fgure 0. To compare the cotrol performaces, results of the covetoal cotrol that a tap of TR are operated o schedule s show Fgure. As a evaluato of the voltage estmato, from LV measured by meters ad estmated voltages Fgure 0, LV of some meters drop by 0.04p.u. from 6h to 0h. O the other had, the estmated voltages drop by 0.0p.u. LV of some meters whch drop by 0.04p.u. fluctuate wdely ad these wave forms are dfferet from LV measured by the other meters. Thus, these voltages clude large uque voltage tred each meter defed Fgure3. The uque voltage tred s ot estmated by estmato based o the voltages of the represetatve meter. O the other had, the voltage cotrol does ot requre measurg some uque voltage treds but all commo voltage treds. Therefore, these estmato errors are ot mportat for the voltage cotrol. Here, the maxmum root mea square (RMS) estmato errors for 4h each category Fgure 8 are descrbed as follows. The maxmum RMS errors are about 0.06p.u. ad the errors are ot greatly affected to the voltage cotrol due to small error. Verror RMS[ p.u.] ( V ) k k V est (0) k Category0.04 Category0.08 Category3 0.0 Category40.08 Category50.05 Category CIRED 07 4/5

5 4 th Iteratoal Coferece o Electrcty Dstrbuto Glasgow, -5 Jue 07 I the voltage cotrol, the covetoal cotrol regulates the voltages from to p.u. The proposed cotrol regulates LV from to p.u. by cosderg LV codtos. As a result, the proposed cotrol mproves LV drop by 0.04p.u. Therefore, t s cofrmed that the proposed voltage cotrol s able to mprove the voltage cotrol performace. Voltage Voltage Voltage SUMMARY Category Category Fgure 8. Categorzg results of LV Ths study proposes the selecto method of represetatve meters, ad the voltage cotrol utlzg the meters to estmate ad to cotrol LV. Cosequetly, t s cofrmed that the voltage estmato ad the voltage cotrol utlzg smart meters s able to estmate all LV ad to mprove the voltage cotrol performace. As future works, we wll evaluate ths proposed voltage cotrol by more realstc codtos such as actual measured voltage by smart meter ad actual etwork. REFERENCES []Melssa A.Pesk, 0, Coservato Voltage Reducto wth Feedback from Advaced Meterg Ifrastructure, IEEE Trasmsso ad Dstrbuto Coferece ad Exposto, Orado []N. Nakamura, 009, Methods for multdmesoal data aalyss, Kyortsu shuppa, Japa, [3]K. Rudo, 006, Desg of Bechmark of Medum Voltage Dstrbuto Network for Ivestgato of DF Itegrato, IEEE Power Egeerg Socety Geeral Meetg, 006 [4]Stavros Papathaassou, 005, A Bechmark Low Voltage Mcrogrd Network, Cgre symposum Power systems wth dspersed geerato: techologes mpacts o developmet operato ad performace [5]K. Ntta, 00, Advaced meterg frastructure for smart grd, Toshba revew, vol.65, No Category Category 3 Category Represetatve Meter Voltage 3σ of e [%].05 Voltages of meters category Dsturbace evaluato depedet factor Tap of TR MV Reactve power of SC * LV Estmated LV Meter umber Fgure 9. Dsturbace evaluato results The meter of No. s selected as represetatve meter. *Base of p.u. s 0MVA A desg value for dsturbace evaluato TR - N06 - N -0.0 Tme[h] Fgure 0. Results of the voltage cotrol utlzg the smart meters MV Tap of TR LV TR Tme[h] Fgure. Results of the covetoal voltage cotrol (Scheduled operato of a tap of dstrbuto trasformer) CIRED 07 5/5