A METHODOLOGY FOR THE DESIGN OF AN ELECTRICITY THEFT MONITORING SYSTEM

Transcription

1 A METHODOLOGY FOR THE DESIGN OF AN ELECTRICITY THEFT MONITORING SYSTEM 1 SOLOMON NUNOO, 2 JOSEPH C. ATTACHIE 1 Lecturer, Department f Electrical and Electrnic Engineering, University f Mines and Technlgy, Tarkwa, Ghana 2 Lecturer, Department f Electrical and Electrnic Engineering, University f Mines and Technlgy, Tarkwa, Ghana ABSTRACT Utility cmpanies in Ghana estimate that electricity theft csts them ver a billin US dllars in annual revenues. The purpse f this wrk is t prvide an algrithm fr the design f electricity theft mnitring system which allws vilatrs t be detected at a remte lcatin. It begins with the analysis f lsses in electrical pwer systems. The bulk f these lsses are caused by electricity theft, rather than ther pssibilities such as pr maintenance and calculatin and accunting mistakes, thugh sme pwer systems may suffer frm bth. Other aspects discussed include the varius frms f theft practices, methdlgy fr detectin f theft, generating the theft case algrithm using the backtracking algrithm methd and cmmunicating these data frm the cnsumer premises t the substatin using the existing pwer lines. Apprpriate cnclusins and recmmendatins were given frm the infrmatin gathered. Keywrds: Electricity Theft, Mnitring System, Algrithm, Pwer Line Cmmunicatin 1. INTRODUCTION Accrding t Smith [1], electricity theft can be in the frm f fraud (meter tampering), stealing (illegal cnnectins), billing irregularities, and unpaid bills. The evidence f the extent f electricity theft in a sample f 102 cuntries between 1980 and 2000 shws that theft is increasing in mst regins f the wrld. The financial impacts f theft are reduced incme frm the sale f electricity and the necessity t charge mre t cnsumers. Electricity theft is clsely related t gvernance indicatrs where higher levels are recrded in cuntries withut effective accuntability, plitical instability, lw gvernment effectiveness and high levels f crruptin. Merely generating mre pwer is nt enugh t meet present day requirements. Pwer cnsumptin and lsses have t be clsely mnitred s that the generated pwer is utilised in an efficient manner. This illegal electricity usage may indirectly affect the ecnmic status f a cuntry. Als the planning f natinal energy may be difficult in case f unrecrded energy usage. This paper discusses the design f an algrithm t mnitr distributin systems fr theft. 2. OERIEW OF THE ELECTRICITY SECTOR IN GHANA The lta River Authrity (RA) and Ghana Grid Cmpany (GRIDC) are respnsible fr generatin and transmissin f electricity in Ghana respectively. Als, the Electricity Cmpany f Ghana (ECG) is respnsible fr the distributin f electricity t cnsumers in the suthern and middle belts f Ghana, viz., Ashanti, Central, Greater Accra, Eastern, Western, parts f Brng Ahaf and lta Regins f Ghana, whereas the Nrthern Electrificatin Department (NED) is respnsible fr the distributin f electricity t cnsumers in the nrthern belt f Ghana, viz., parts f Brng Ahaf, Nrthern, Upper East and Upper West Regins f Ghana. A sketch f the electric pwer generatin, transmissin and distributin netwrk in Ghana is as shwn in Figure 1. Cnsumers n the distributin system are categrized as industrial, cmmercial and residential. Industrial cnsumers use f energy is fairly cnstant, bth ver the day and ver seasns. 112

2 Figure 1 - Electric Pwer Generatin, Transmissin and Distributin Netwrk in Ghana Hwever, that f cmmercial users is less cnstant and varies ver the day and seasns. Residential and cmmercial uses are mre variable, smetimes changing rapidly ver the day in respnse t ccupant needs and appliance use. Amah [2] states that, as f December 2003, the entire distributin system f Ghana cmprised f 8,000 km f sub-transmissin lines, 30,000 km f distributin netwrks with 22 bulk supply pints and 1,800 MA f installed transfrmer capacity. Pwer distributin systems prvide pwer t custmers thrugh pwer lines. 3. ANALYSIS OF LOSSES IN POWER SYSTEMS Lsses ccur at all levels, frm generatin, thrugh transmissin and distributin, t the cnsumer and the meter. It is nrmally at the distributin level where the majrity f avidable lsses ccur. All electrical pwer distributin cmpanies perate with sme accepted degree f lsses. This is n different frm the scenari in Ghana. Lsses incurred in electrical pwer systems have tw cmpnents: Technical lsses and Nn-technical lsses (Cmmercial lsses) 3.1 Technical Lsses Technical lsses will always arise as the physics f electricity transprt means that, n pwer system can be perfect in its delivery f energy t the end custmer. Technical lsses are naturally ccurring lsses (caused by actins internal t the pwer system) and cnsist mainly f pwer dissipatin in electrical system cmpnents such as transmissin lines, pwer transfrmers, measurement systems, etc. Technical lsses are pssible t cmpute and cntrl, prvided the pwer system in questin cnsists f knwn quantities, viz., resistance, reactance, capacitance, vltage, current and pwer. These are rutinely calculated by utility cmpanies as a way t specify what cmpnents will be added t the systems. Lads are nt included in the lsses because they are actually intended t receive as much energy as pssible. Technical lsses in pwer systems are caused by the physical prperties f the cmpnents f pwer systems. Example, I 2 R lss r cpper lss in the cnductr cables, transfrmers, switches and generatrs. The mst bvius example is the pwer dissipated in transmissin lines and transfrmers due t their internal impedance. Technical lsses are easy t simulate and calculate; cmputatin tls fr calculating pwer flw, lsses, and equipment status in pwer systems have been develped fr sme time. The instantaneus pwer lss, P lss (t) in a transmissin line can be expressed as: P lss ( t) P ( t) P ( t) = 1 surce lad where P surce (t) is the instantaneus pwer that the surce injects int the transmissin line and P lad (t) is the instantaneus pwer cnsumed by the lad at the ther end f the transmissin line. Thus the energy lss, W lss, is given by: = b lss a lss () t W P dt 2 where a and b are respectively the starting pint and ending pint f the time interval being evaluated. It must be nted that a fairly accurate descriptin f P lss (t) as a functin f time is always needed t make a reliable predictin f W lss. 3.2 Nn-Technical Lsses (Cmmercial Lsses) These refer t lsses that are independent f technical lsses in the pwer system. Tw cmmn 113

3 examples f surces f such lsses are cmpnent breakdwns that drastically increase lsses befre they are replaced and electricity theft. Lsses incurred by equipment breakdwn are quite rare. These include lsses frm equipment struck by lightning, equipment damaged by time and neglect. Mst pwer cmpanies d nt allw equipment t breakdwn in such a way and virtually all cmpanies maintain sme frm f maintenance plicies. Other prbable causes f cmmercial lsses are: Nn-payment f bills by custmers Errrs in technical lsses cmputatin Errrs in accunting and recrd keeping that distrt technical infrmatin. Inaccurate r missing inventries f data n custmers The mst prminent frms f cmmercial lsses in Ghana are electricity theft and nn-payment f bills. Nn-payment, as the name implies, refers t cases where custmers refuse r are unable t pay fr the electricity used. Hwever, the ther frms are nt analyzed thrughly in this prject. Nntechnical lsses are very difficult t quantify r detect and are mre prblematic than the ther lsses. Nn-technical lsses can als be viewed as undetected lad; custmers that the utilities d nt knw exist. When an undetected lad is attached t the system, the actual lsses increase while the lsses expected by the utilities remains the same. The increased lsses will shw n the utilities accunts, and the csts will be passed t custmers as transmissin and distributin charges. Research has shwn that, transmissin and distributin csts in Ghana are calculated as part f the custmers bills, while in ther cuntries, custmers are usually charged a single flat energy rate that includes all services. This means that, the transmissin and distributin lsses that increased due t cmmercial lsses wuld be charged either t the existing custmer whse pwer lines are illegally tapped, r the utility, depending n the methd f theft. Bth ECG and NED lsses range frm 24 t 30 percent f pwer generated, cllectin rates range frm 75 t 85 percent f billing and arrears frm gvernment agencies significantly weaken balance sheets [3]. In recent years, ECG has undertaken several measures t reduce lsses. Figure 2 shws the ttal distributin lsses f ECG frm 1985 t Frm the figure, it is bserved that lsses were relatively lw between 1993 and 1996 but increased thereafter. 3.3 Electricity Theft as a Majr Cmpnent f Cmmercial Lsses Cmmercial lsses arising thrugh electricity Figure 2 - Ttal Distributin Lsses f ECG,

4 theft and ther custmer malfeasances is a universal prblem in the electricity supply industry. Such lss may ccur by a number f means, such as meter tampering, illegal cnnectins, billing irregularities, and unpaid bills. The assciated identificatin, detectin, and predictin prcedures are imprtant fr many utilities, particularly thse in develping cuntries like Ghana. Currently, mst slutins are ad-hc and can nly be implemented after a lng perid f detectin and bservatin. The use f electricity is cnsidered illegal if: Electrical energy is cnsumed withut legal agreement between the prviders and cnsumers. The cnsumer des nt cmply with the agreement clauses fr the cnsumed energy such as entirely r partially nt measuring the energy cnsumed and intentinally enfrcing an errr t the measuring device (Watt-hur Energy Meter). In Ghana, meter inspectin is the main methd f cmmercial lsses detectin because the majrity f electricity theft cases invlve meter tampering r meter destructin. The principles f peratin fr watt-hur meters essentially have nt changed since the 1880s and the 1890s, when the watt-hur meter was invented. But the way f cnstructin keeps n changing. In sme areas in Ghana, the lads are nt metered r are metered cmmunally rendering any lss calculatins (technical r nt) fr that area useless. The majrity f electricity theft cases invlves meter tampering r meter destructin and ften after ne has been discnnected fr nnpayment f bill. 4. METHODOLOGY FOR DETECTION The methd includes receiving meter data f the measured pwer cnsumed by a custmer, receiving delivered pwer data that includes data f the pwer delivered t the custmer, determining a difference between the meter data and the delivered pwer data, determining that the difference between the meter data and the delivered pwer data is greater than a predetermined amunt, and indicating a discrepancy if the difference between the meter data and the delivered pwer data is greater than a predetermined amunt. In additin, the methd may include determining that a discrepancy varies ver time by a predetermined amunt and prviding a discrepancy ntificatin thrugh pwer lines. The blck diagram in Figure 3 shws the basic cmpnents f the system mentined. Figure 3 - Blck Diagram shwing the Methdlgy fr Detectin 115

5 4.1 Mathematical Mdeling f the Theft Case Algrithm In this paper, the backtracking algrithm was used fr the analysis. Backtracking is a refinement f the brute frce apprach, which systematically searches fr a slutin t a prblem amng all available ptins. Backtracking algrithms are distinguished by the way in which the space f pssible slutins is explred. Smetimes a backtracking algrithm can detect that an exhaustive search is unnecessary and, therefre, it perfrms much better. Figure 4 will be used fr generating the necessary algrithms. The pwer, P, in an electrical system is given as: Nte that fur scenaris can be derived frm Equatin 6. These are: {[ + φ )] [ 1 m + φ )]} ( ) + φ ) {[ ( ωt + φ )] [ sin( ω )]} sin t φ 8 {[ ( ω t φ )] [ sin( ω + )]} sin t φ 9 {[ φ )] [ 1 m φ )]} ( ) φ ) 7 Figure 4 - Blck Diagram f the Cmparisn Unit P = I csθ 3 and the instantaneus current is als given as: () t = I ( ω t ± φ ) I m sin 4 Let I 1 (t) = I sin(ωt ± ) be the input current t the meter and I 2 (t) = I sin(ωt ± ) be the utput current t the meter. Assuming that the internal circuitry f the meter is purely resistive, then the crrespnding input and utput vltage relatins are 1 (t) = sin(ωt ± ) and 2 (t) = sin(ωt ± ) respectively and these will frm as the input signals fr the cmparatr. Therefre the utput vltage,, frm the cmparatr is given as: ( ) Thus, {[ ( ω t ± φ )] [ sin( ω ± )]} sin t φ 6 10 Either Equatins 7 r 10 culd be used fr the cmparisn because fr a purely resistive circuit, the phase will remain the same at bth the input and the utput. Cnsequently, shuld the amplitude difference,, exceeds a predetermined value, then a theft case will have ccurred and it is fed int a vltage-t-frequency cnverter t generate a peridic utput wavefrm having a frequency prprtinal t the magnitude f an applied DC input vltage. Fr any discrepancies recrded, the current in the system will vary. Ntably, an n-ging theft case will lead t an increase in current. Figure 5 prvides flwchart f hw the cmparisn blck in Figure 3 will perate. When the mains is switched n, input and utput signals f the watt-hur meter is cmpared t check fr any discrepancies. When there is n discrepancy recrded, a green LED at the substatin will be ON till a discrepancy ccurs. With a discrepancy 116

6 Figure 5 - Flw Chart f the Cmparisn Blck recrded, a red LED at the substatin turns ON t ntify the peratr. After ntifying the peratr that a discrepancy has ccurred, the cnsumer data will als be recrded. The data will include the meter number, the time the prblem started and the apprximate lcatin. When all the data has been taken, the nearest substatin is ntified and the peratin is stpped r the mains turned OFF. All the sensr devices in the cmparisn unit will be lcated alng the Lw ltage pwer lines and alng the Medium ltage pwer lines since they are the main lines where theft can take place. 5. CONCLUSIONS Electricity theft, a cmmn frm f cmmercial lsses, invlves tampering with meters t distrt the billing infrmatin r direct cnnectins t the pwer system. Cmmercial lsses are nearly impssible t measure using traditinal pwer system analysis tls. This is due t the lack f infrmatin n bth cmmercial and the legitimate lads in the system, which translates t insufficient inputs fr any meaningful lss calculatins. Despite the best effrts by utilities, the current results f cmmercial lsses measurements are ften inaccurate at best, because the figures rely heavily n the recrds f detected cases, rather than by actual measurement f the electrical pwer system. Certainly utilities have sme cntrl ver the magnitude f cmmercial lsses; but even with their best effrts, sme cmmercial lsses will still cntinue. An algrithm fr the design f electricity theft mnitring system has been generated using the backtracking algrithm type. ACKNOWLEDGEMENT The authrs will like t express their heartfelt gratitude t James Owusu Mintah fr his effrts during the data cllectin. REFRENCES: [1] T. B. Smith, Electricity Theft: a Cmparative Analysis, Energy Plicy, lume 32, Issue 18, December 2008; 2003, pp [2] A. Amah, Guide t Electric Pwer in Ghana, First Editin, Resurce Centre fr Energy Ecnmics and Regulatin, Legn; 2005, 89 pp. [3] PURC, Annual Reprt retrieved n 25th January, 2009 at 8:09pm frm rt.pdf;