AUTOMATING CONSUMERS CONNECTIONS TO THE DISTRIBUTION NETWORK FOR ENHANCED PERFORMANCE

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1 Internatonal Revew of Electrcal Engneerng (I.R.E.E.), Vol. 5, n.5 AUTOMATING CONSUMERS CONNECTIONS TO THE DISTRIBUTION NETWORK FOR ENHANCED PERFORMANCE O.M. Popoola 1, A. Jmoh 2, D.Ncolae 3 Abstract Tral and error approach whch nvolves servce nterrupton s usually carred out to resolve unbalance on phases n power dstrbuton system. Ths approach mght mprove the phase voltage and current but the resultant effect (change) does not last for too long; thereby reduces the market value n terms of qualty and relablty of supply. To enhance the performance of the secondary dstrbuton system there s a need for an automatng technology. The am of ths paper s to ntroduce a method and technology developed for resolvng mbalances n a secondary dstrbuton system as a result of the uneven dstrbuton of sngle phase load across a three phase power system. The technology developed s able to montor, acqure/dsplay collected data and perform self changng swtchng actons electroncally. Ths acton s n form of rearrangement or transfer of consumer loads for optmal performance of the dstrbuton feeder. The proposed swtchng technology s based on open- transton swtch that enables transfer or rearrangement of consumer loads n a three-phase system wthn mllseconds wth supervsory control system. The followng methodologes: System Smulator - Matlab (Smulnk), Vrtual Instrumentaton-Lab VIEW and Hardware mplementaton were appled for the valdaton of the proposed technque. Keywords: Automated technology, Current mbalances, Load balancng, Phase arrangement, Statc transfer swtchng. I. Introducton Electrc utltes are facng the demands of reducng costs and mprovng the qualty as well as consstency of supply. The dstrbuton network s an mportant part of the total electrcal supply, as t transports electrc power from the dstrbuton staton to the customers. Conversely, t has also been reported that 80% of the consumer servce nterruptons are due to falure n the dstrbuton network. Ths s as a result of subjecton to load varatons whch mght be due to load growth and the delay/non response to the need for constructon of new substatons and feeders wthn the system [1]. The dstrbuton systems have suffered from the followng malades, manly: voltage and current mbalances beng a major factor; poor voltage regulaton; peak power/energy losses; conductor heatng/equpment damages; very hgh unaccounted energy losses (20-40% aganst nternatonal standards of 8-10%) [2] [4]. Dfferent methods from the standpont of feeder loss reducton and load balancng have been proposed, researched, and presented for mprovement of dstrbuton network reconfguraton; however these were manly on the prmary dstrbuton system [2 11]. The dstrbuton network s normally nsttuted at the prmary sde or medum voltage level of dstrbuton network; however t has lttle or no sgnfcant nfluence on the problem created at the secondary sde or the low voltage levels. Although, techncally these sngle-phase loads are arranged such that the 3-phase system s balanced; the fact, however, s that 100% balanced operaton all the tme s mpossble. At best what happens s that the unbalanced s mantaned wthn a statutory level. Unbalance n the secondary dstrbuton network ncreases the severty of the problems of voltage drop, power losses and large current n the neutral wre [12], [13],[17]. Normally, to attan load balancng on phases, a conventonal tral and error approach s used. Ths nvolves feld measurements and the applcaton of one s judgment. Usng ths approach, the phase voltage and current unbalances mght mprove, however the resultant change usually does not last for a long perod of tme [14]. Wth ths approach servce nterrupton s unavodable; hence the rearrangement of consumers load dstrbuton ponts on phases cannot be performed frequently so that a level of servce supply can be mantaned to the consumers. Although a method by Adsa, St & Davdson [15] for assstng one s judgment n the conventonal tral and error approach was presented, however ths s stll nsuffcent as a result of the tme-varyng characterstc of load. An optmal soluton n the form of automaton mplementaton usng artfcal ntellgence, telecommuncaton and power electroncs equpments n power systems wll guarantee contnuous dynamc load balancng along the low voltage secondary feeder thereby relevng overload n the three-phase system wth mnmal servce nterrupton; and reduce real power losses. Ths Manuscrpt receved February 2010, 2427 Copyrght 2007 Prase Worthy Prze S.r.l. - All rghts reserved

2 O.M. Popoola, A. Jmoh, D. Ncolae wll be techncally advantageous as well as economcal for the utltes and the customers. Ths paper addresses a method and technology for mplementaton, ntended for enhancng performance of the low voltage dstrbuton network. The paper commences wth the problem formulaton, followed by the proposed soluton method; and the valdaton of the proposed technque as carred out at our laboratory n South Afrca. The remander of the paper s devoted to deductons and realzaton of the automatng technque to reduce unbalance to a mnmal level at the LV dstrbuton network [15], [16]. II. Problem Descrpton Recent researches has shown that, modfyng the radal structure of the prmary feeders from tme to tme by changng the on/off status of the sectonalzng and te swtches to transfer load from feeder to another may mprove the operatng condtons of the overall system sgnfcantly. Ths usually has no consderable effect on the secondary sde of the dstrbuton network, especally ts relablty. Majorty of the consumers at the secondary dstrbuton are sngle phase loads. Often tmes these sngle phases are arranged or grouped to have a balanced three phase systems, however, unbalance stll occurs due to unequal (unevenly) load dstrbuton among the phases of the feeder durng tme of use. Hence the need to evolve a technque to mnmze the unbalance effect (reduce power losses, voltage drop and etc) by transferrng loads from the heavly loaded to less loaded phases randomly. In formulatng ths problem, certan predefned objectves must be satsfed n the redstrbuton of the load among phases [17], [18],[19]. In ths case the objectve functons that are consdered are dscussed n the followng: II.1 Objectve Functons to be acheved a. Total Complex Power Unbalanced In a three phase load system, the complex powers are expressed as (j = a, b, c) for the loadng of each phase. j S The unbalance of these three complex powers can be evaluated as follows: c 2 ul j d 1/ 3 ja s s s (1) d Where S represent the deal per phase loadng and s d c j 1/3 s (2) ja Ths s consdered for a typcal feeder th. thus an ul evaluaton of s 0 ndcates that the complex power of th feeder s balanced. The total complex power unbalance can be evaluated from: s ul T n s 1 ul (3) Where n s the number of feeders wthn the object feeder. s used to evaluate the complex power unbalance of a feeder and the value of ths descrbes the load balance stuaton at every feeder. Thus mnmzaton of s an objectve functon n the proposed method. ul s T ul s T b. Average Voltage Drop A good load balance wll generally reduce the voltage drop. Reducng the voltage drop s also an mportant objectve for a dstrbuton engneer to acheve. The average voltage drop s expressed as: m V 1/ m VD (4) d 1 Where m s the number of load ponts for the feeder under consderaton and m p rated j / rated j1 VD V V V (5) Where V rated s the rated phase voltage; p V j s the magntude of the phase voltage at load pont and VD s the average of the three phase voltage drop at load pont. c. Voltage unbalance Factor The total voltage unbalance factors for the zero and the negatve sequence are expressed as: m 1/ / VUF 0 m V 0 V (6) 1 m 1/ / VUF m V V (7) 1 d. Total Lne Loss Mnmzng the system loss and mprovng the operatonal effcency are usually major objectves of a power utlty. Hence the mnmzaton of lne losses s also an objectve functon consdered n the redstrbuton of loads presented n ths work. m / 2 loss 1 P r P Q V (8) Although conventonal tral and error approach s used for mprovng load balancng on the secondary level, the duraton of the effects of the balancng vares from one dstrbuton feeder to another due to the sngle phase loads that contnually change across the three-phase feeder [9,10], apart from the tme, human resources and etc spent on achevng t. The man am of ths study s to research and propose a method and technology for automatcally mnmzng the unbalances n the feeders and enhancng the secondary dstrbuton network performance wth the vew to acheve the followng: Rearrangement of consumers loads among the phases unformly so as to acheve load balance at the secondary dstrbuton level. Copyrght 2010 Prase Worthy Prze S.r.l. - All rghts reserved Internatonal Revew of Electrcal Engneerng, Vol. 5, n

3 O.M. Popoola, A. Jmoh, D. Ncolae To elmnate or reduce tral and error (manual operatons) methods. Evolve technques or system for ensurng contnuous dynamc on-lne load rearrangement wth mnmal servce nterrupton. Ensure that unbalance s wthn the specfed lmt as: a detaled desgn (llustrated by a block dagram) of the proposed technology s shown n Fgure 3. VUF max Vab, Vbc, Vca V mean / Vmean % lmt (9) Where V ab, V bc, V ca represents the lne to lne voltages and V mean = mean (V ab, V bc, V ca). II.2. Phase and Load Balancng Usually the load consumpton of consumers connected to a feeder fluctuates, thus leadng to the fluctuaton of the total load connected to each phase of the feeder. Ths n turn mples that the degree of unbalance keeps varyng. To balance the phase currents n every segment and reduce the neutral lne current s a very dffcult task for the dstrbuton engneers consderng the fact that they do not have control over the utlzaton by the consumers. Tral and error approach s based on expert knowledge and judgment whch nvolves the analyss of varety of nterrelated meter ndcatons to detect abnormal condtons such as crcut overloads, mproper lne voltages, etc. Other factors requred n the exercse nclude the knowledge of voltage regulatons, load flow analyss and mnmzaton of crcut losses; use of mathematcs to calculate resstve and reactve loads and phase relatonshp to dentfy unbalanced low effcency load, crculatng currents and undesrable condtons. Wth the correct technology and provson of the requred nput nformaton(s), most of these actvtes can be programmed to be performed by a dedcated mcrocontroller or processng unt. Fg 1: Proposed System Block Dagram Fg 2: Typcal model layout scheme of the proposed system III. Proposed Technque In the development of a technque for rearrangement of consumer load to mnmze unbalance n a low voltage dstrbuton system, the key operatonal actvtes dentfed n relaton to the feeder system ncludes montorng and acquston of data; processng and communcaton of sgnal and data; control and swtch transfer. These actvtes can be acheved by separate functonal unts namely: (1) the swtchng unt and (2) sensng unt whch together wth the supervsory control staton forms the ntellgent unt package for the proposed technology. The block dagram n Fgure 1 & 2 shows the nteracton of the functonal unts of the proposed technque and a typcal scheme layout of a consumers connecton to a feeder. To assst n the knowledge of performance capabltes, operaton features, and ntegraton of functons of the ntellgent unt package a practcal and economc realty, Fg 3: Schematc dagram of the proposed Technology The package conssts of the followng man components: Swtchng devce: Made of three phase ac statc swtch as well as operatng mechansm (actuator-control unt) that s capable of openng and closng the swtchng devce remotely (dgtal sgnal processng). Sensng unt: Ths unt dependng on the problem formulaton and soluton technque or algorthm, whch may be current or any other quantty at the consumer s connecton node s requred for montorng of the system condtons; collecton of nput data; converson of analogue sensor sgnal nto dgtal data that can be recognzed by mcrocontroller; and communcaton wth the supervsory control staton. Copyrght 2010 Prase Worthy Prze S.r.l. - All rghts reserved Internatonal Revew of Electrcal Engneerng, Vol. 5, n

4 O.M. Popoola, A. Jmoh, D. Ncolae Supervsory Control unt: conssts of embedded mcrocontrollers for effectve co-ordnaton, computatonal and control of other ntellgent unts. Communcaton unt: a means of data communcaton between the swtchng unt, sensng unt and the supervsory control staton. And lastly, unnterruptble power supply unt capable of powerng all components of the package. The fundamental concept of the proposed technology s based on the open-transton swtch that enables the transfer or rearrangement of consumer loads n the threephase feeder system wthn mllseconds. Ths s made possble through supervsory control system for effectve co-ordnaton, computatonal and control of other ntellgent unts. III.1. Constructon of Proposed Technology Startng wth the swtchng unt as shown n Fgure 3, ths comprses manly the statc transfer swtches (STS) and the sub control. The statc transfer swtch s made of two par of thyrstor connected n nverse parallel for each phase. Durng normal operaton one of the statc transfer swtches s n ON mode or close poston (example S1) allowng the conducton of current to the load (consumer) whle the other two par of statc transfer swtches (S2 & S3) are n the OFF mode or open. When the rearrangement (transfer) operaton s requred due to overload on the current phase (example S1) beng used, S2 or S3 s turned on to conduct the current to the load from the phase that can accommodate the exstng consumer and balance (or mnmze the unbalance) of the three phase feeder. Then the current n S1 s blocked at the frst zero crossng. The control actons sent from the supervsory control (SC) s carred out through a logc swtchng crcut actng as the operatng mechansm or better known as the actuator. The actuator s part of the sub control. The sub control (S bc) s nterlnked wth the SC and located on the lne. It s desgned to acqure data, swtchng status and transfer same to the SC through a communcaton nterface (Wreless Broadband Access lnk) and also to perform swtchng acton. The montored nformaton (from the sensng unt desgn) and the command (control) sgnal to swtches S1 or S2 or S3 to perform a transfer operaton from Phase 1 (Red) to Phase 2 (Blue) or Phase 3 (Yellow) when the preferred source voltage or current devates from the pre-set upper or lower lmt s sent from the SC va the S bc. III.2. Operatng and Control Scheme As shown n Fg. 3 and 4, voltage sensng devce contnually montored the voltages on each of the phases whle current transducer montored the current on the phase on whch the load s connected. The montored nformaton s transmtted from the sensng unt va (usng) wreless communcaton to the SC staton where decsons are takng based on the soluton algorthms. These decsons are n relaton to the problem of fndng a condton of balancng as expressed mathematcally by St et al. [6] usng current system for a random pont of connecton k n a network wth 3 phases and shown n the equatons 10, 11 & 12. STOP NO YES SUPERVISORY CONTROL 3 Phases Balance? IR=IY=IB Algorthms Processor IR IY IB Measured Values Measured Values Measured Values Swtchng Control Sensors Sensors Sensors Fg 4: Flow process of the proposed system Consumers (10) I sw I I ph1k k k ph1k (11) I sw I I ph2k k k ph2 k (12) I sw I I ph3k k k ph3 k 1 1 where, I ph1k, I ph1k and I ph1k represent the currents (phasors) per phase (1, 2 & 3) after the k pont of connecton; sw k are dfferent swtches; whle I k represent dfferent load currents connected to the dstrbuton system at pont k of connectons. In the case of unbalance, the SC sends the command sgnal to S bc of the swtchng unt for the statc transfer swtch (S1) of load I k va wreless communcaton to open, whle wthn a mcro second a sgnal s sent to S2 or S3 of the same load I k to close. IV. Software Valdaton The valdaton to test the operaton and behavor of the proposed technology was carred out usng the Smulaton and Vrtual mplementaton methodologes. IV.1. Smulaton The operaton of the proposed system was modeled usng the MATLAB 6.5 verson as shown n Fgure 5. The smulaton results shown n Fg. 6 below conssts of three-phase source; a constant mpedance load wth a power factor of 1. Ideal thyrstor were used for the desgn of the swtchng crcut. Ant-parallel thyrstor are used to create the ac swtch (statc). a. Transfer durng Voltage Unbalance. Under normal condtons, statc swtch (S1) s turned on and current flows from the prmary source to the load; when current unbalance s detected by the supervsory Copyrght 2010 Prase Worthy Prze S.r.l. - All rghts reserved Internatonal Revew of Electrcal Engneerng, Vol. 5, n

5 O.M. Popoola, A. Jmoh, D. Ncolae control; the gate sgnal s removed from S1. Snce swtch S1 has a hgher voltage potental than ac swtch S2, the gatng sgnal of S2 must be held off untl ac swtch S1 naturally commutates (allowng fnte tme to elapse). The mnmal transfer tme, n ths smulaton, s between to 3-5 msec from the start of the unbalance due to hgh nductve load as shown n Fg. 6; the maxmum transfer tme could be 17 msec whch s not consdered as a voltage dp [20]. other sub VI. The modules and some of the task performed are outlned below: SUPERVISORY CONTROL STATION WIRELESS COMMUNICATION d e c s o n Control Sgnal SENSING UNIT SENSOR (Current Transformer) SWITCHING CIRCUIT DISTRIBUTION FEEDER (3-PHASE) SWITCHING UNIT CONSUMER Fg 7: Block Dagram Outlnng the Approach n Lab VIEW Fg 5: Smulaton model desgn of the proposed scheme Fg 6: Current transfer operaton IV.2. Smulaton In ths secton adaptve representaton of the proposed technology and ts multple executon operaton was smulated and studed n relaton to the focus of ths paper. The vrtual mplementaton was carred out usng a Workstaton-Intel Pentum CPU 1.90 GHz, 256 MB of RAM havng a verson of Lab Vew 7.0. The process control, as well as acquston, processng, storng and reportng of all data, s acheved through the vrtual nstrument (VI). For the dstnct blocks, dfferent vrtual nstruments were created usng the block dagram approach n Fgure 7. The program wth the functons n the vrtual nstrumentaton are created and shown as module. The module s made of varous subs VI; to facltate and perform dfferent operatons; and communcate wth. Module 1: VI for source supply Generates and produces the nstantaneous voltage. Dsplay of numercal data and phase ndcator of the varaton of the nstantaneous voltage on a computer screen.. Module 2: VI for fundamental of AC crcut, montorng of the system varables and part of the sensng unt. Generates the phase voltage, the lne voltage and lne currents. Montorng of lne current for decson makng at the supervsory control staton and conveyance of decson for any necessary acton. Computaton of the actve, the reactve and apparent power usng the resultant numercal capture data of the I-V dsplay after the phase angle s determned. ) Module 3: VI for the swtchng operaton (swtchng unt) of the proposed technque Development of a swtchng unt as shown by the logc crcut operatng on the Boolean propertes and prncples; and sgnal to perform transfer operaton. v. Module 4: VI to montor phase dsplacement and transfer. Ths s facltated by the case structure nterlnked wth Module 3 and phase transfer reflected n module 4 outputs. v. Module 5: VI for Montorng and Graphcal dsplay of the I-V characterstc n terms of unbalance. Lnearzaton of the I-Vs scans through a program nputted nto the objects n Lab VIEW. Characterzaton of the performance of the three phase supply (feeder) n relaton to unbalance. v. Module 6: VI for Synchronzaton of the Actvtes of the Proposed Technology VI block panel model of the proposed technology as shown n Fgure 8 was developed usng the module outlned above. Dfferent scenaros were carred out n order to verfy the operatonal performance of the Copyrght 2010 Prase Worthy Prze S.r.l. - All rghts reserved Internatonal Revew of Electrcal Engneerng, Vol. 5, n

6 O.M. Popoola, A. Jmoh, D. Ncolae proposed technque as computatonal and graphcally shown n Fg. 9 and 10 a. Test : Rearrangement of Consumers for Optmal Performance of a Three-Phase Feeder Fgure 9 and 10 represents unbalanced scenaros n a three Phase feeder network. The frst scenaros (Fg. 9) represents an unbalance state due to the ensung unequal load among the phases Red, Yellow (Whte) and Blue (Z 1, Z 2, Z 3). Fgure 10 shows an unbalance scenaro on the dstrbuton feeder attrbuted to the resultant load dstrbuton on a partcular phase - the consumer loads (Z 21, Z 22, Z 23) on Yellow Phase whch eventually affects the total load Z 2, Z 1, Z 3 of each phase thereby makng the feeder unstable. Sgnal (waveforms) of the phase voltage, the lne voltage, the load current and the numercal data (values) of the electrcal nput and output parameters for each scenaro are dsplayed on the computer screen as shown. An ntal samplng rate of 10 Hz at every 10 samples of data gave very sluggsh sgnal plot response. Ths was stepped up durng the test to a samplng rate of 1000Hz usng 100 samples at a lag tme of 100ms whch was use for loggng data/test. Result & Observaton The unbalance scenaros n Fgure 9 & 10 wth a value of 0.021(2.11%) & 0.020(2.02%) were resolved usng the proposed technology, as shown n Fg. 11 & 12. Loads were arranged such that the resultant load on each phase s equal or approxmate as shown n Fgure 11; the Consumer usng swtch 1 s swtched to the BLUE phase from the RED phase, Consumer usng swtch 2 s stll on the YELLOW phase as prevous and Consumer usng swtch 3 s swtched over to the RED phase. In Fgure 12, the consumer load (Z 21) s transfer or changed from the YELLOW Phase to BLUE Phase whch can accommodate the load thereby achevng mnmal unbalance on feeder accordng to the statutory standard. For the computaton of the unbalance at the supervsory control, the ANSI defnton of voltage unbalance among the other standards but expressed n terms of current unbalance was appled for operatonal and demonstratve purpose. Other standards can be appled. where I R, I Y and I B are the phase current of R, Y, B, I max and I mn are the calculated maxmal and mnmal phase currents. Concluson From the dfferent scenaros, the transfer of consumer wthn the phases was accomplshed wthn mllsecond due to automaton of the swtchng devce, whle computatonal functon was able to show the state of the feeder at any pont n tme n both numercal value and dsplay (ndcator) forms, thereby assstng the operator to known the feeder state at a glance. From the waveforms, the sgnal for transfer operaton and the control algorthms are factors that ad the act of the proposed technque. Summng up the observatons, proposed technology performance s dependent on the computatonal aspect of the unt and the transfer tme (whch s nclusve of when the sgnal s receved for transfer). V. Expermental Implementaton For the mplementaton of swtchng unt of the proposed technology usng electronc components, the schematc dagram n Fg 13 was used. The test was performed wth and wthout the safety devce usng a varable three phase power supply at 220 V rms; ncandescent lamp of 100 W 230 V as load; a rotary swtch for change of phase. A Tektroncs 2000 seres dgtal osclloscope 4 channels as was used as the test faclty (Fg. 14). Hardware Result The real tme voltage and current waveforms of the test crcut of Fgure 14 s shown by the osclloscope and graphcal output n Fgure 14 & 15. The three - phase voltage supply s shown by the waveform n Lght Blue, Red and Dark Blue. Each havng a peak value between 290 and 311V as shown by a dvson of 10 V representng 100V on the y-axs; the resultant V rms 205 V 220 V. The phase dsplacement s ±120. The magntude of the current (I rms) s A 0.5A or peak value of 0.65 A as shown by the green snusodal waveform. The output shows that there are some transent s effects as a result of the use of the trac. Current unbalance = 3(I max-i mn)/(i R+I Y+I B)*100% (13) Copyrght 2010 Prase Worthy Prze S.r.l. - All rghts reserved Internatonal Revew of Electrcal Engneerng, Vol. 5, n

7 Internatonal Revew of Electrcal Engneerng (I.R.E.E.), Vol. 5, n.5 Fg 8: Proposed Technology for Optmal performance Block Panel Fg 9: Unbalance scenaro on the LV dstrbuton feeder (3-Φ) Manuscrpt receved February 2010, 2433 Copyrght 2007 Prase Worthy Prze S.r.l. - All rghts reserved

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9 O.M. Popoola, A. Jmoh, D. Ncolae Fg 10: Unbalance scenaro on LV feeder (uneven load dstrbuton on a phase) Fg 11: Change of Consumer Phases to acheve Balance on the Three Phase Feeder System (Blue, Yellow and Red) Copyrght 2010 Prase Worthy Prze S.r.l. - All rghts reserved Internatonal Revew of Electrcal Engneerng, Vol. 5, n

10 O.M. Popoola, A. Jmoh, D. Ncolae Fg 12: Change of Consumer (Z 21) from Yellow Phase (Z 2 consumers) to Blue Phase to mnmze Unbalance on (3-Φ) Fg 13: Schematc dagram ncorporatng the Safety devce Fg 14: Expermental Set Up of the Proposed Scheme at the Laboratory Transfer Transfer Operaton of the swtchng unt The transfer operaton of the proposed swtchng technology s shown n Fgure 15. The transfer tme shown was more than the 5 msec. Ths s due to the use of a rotary swtch; as well as the commutaton tme of the swtch (trac or thyrstor) beng takng nto consderaton. Ths tme can be consderably reduced usng an automatc or remote control devce to at least 5 ms as depcted n Fgure 6. As shown n Fgure 15 and 16, the load current s n phase wth the supply voltage when transfer operaton takes place. Copyrght 2010 Prase Worthy Prze S.r.l. - All rghts reserved Internatonal Revew of Electrcal Engneerng, Vol. 5, n

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12 Internatonal Revew of Electrcal Engneerng (I.R.E.E.), Vol. 5, n.5 The transent generated or transmtted from the power supply (load crcut) dd not affect the sgnal crcuts as demonstrated by the transfer operaton waveform n Fgure 16. Ths was as a result of the opto-coupler MOC 3084 that has the capablty of beng use wth statc transfer swtch) n the nterface of logc system or control wth equpment power from low voltage ac source. connected as shown (example, u4 and u5; u6 and u7; u8 and u9) n Fgure 14 are ncorporated nto the proposed technology swtchng unt for safety purpose. Under normal condtons, assumng S1 s turned on (u4 and u5 n normal closed poston (NC)) and current flows from the prmary source to the load. When unbalance s detected, S1 s turned OFF by removal of the gate sgnal; S2 receves a gate sgnal to start conducton to accommodate the load. Assumng S1 s stll turned ON due to the commutaton tme, u5 and u9 (S2 swtch) wll reman n the open poston untl the commutaton process s acheved before closng. At no tme wll there be the possblty of two phases beng n the ON mode at anytme. The resultng waveform to depct the operaton has been shown n Fgure 15. Fg 15: Transfer of Load from one Phase to another Phase VI. Economc Consderaton and Vablty Ths proposed scheme does not ental any recurrent expendture (runnng costs) whle the captal cost of the scheme n terms of mplementaton wll be easly pad off wthn a short perod n tme. Ths s as a result of the elmnaton of techncal problems and overhead costs (labor cost for repars, transportaton, travel expenses, loss tme and etc). The contnuous supply to consumers and elmnaton of unantcpated captal cost wll defntely ncrease the energy revenue generaton capacty of the power utlty. The technologes for the key operatonal actvtes such as meterng sensors, data acquston devces, mcro controllers, statc power swtches, data communcaton (wreless) and actuators are already n exstence; playng major roles n smart grd systems operaton. Due to ther applcablty n dfferent operatons and developments nowadays, ther respectve cost s mnmal thereby makng the actualzaton of ths scheme realzable and cost effectve. Fg 16: Surge current as a result of load beng connected Although there was consderable tme for the swtch to naturally commutates, there s a need to consder the safety of the followng: the customer both n terms of ndvdual and equpment; the dstrbuton system (Three- Phase Feeder) as well as the proposed technology; and also how to assst the operatonal personnel n the dstrbuton staton. In order to acheve that, a safety devce was ntroduced as shown n Fgure 13, bearng n mnd that one of the purposes of ths proposed technology s to ensure contnuous dynamc on-lne load arrangement wth mnmal servce nterrupton. Desgn and operaton of the safety devce Two Opto-solator swtches havng ther dc supply from the source supply of each phase but ntegrated and VII. Concluson The methodology proposed for rearrangement of consumer on phases was llustrated, smulated and demonstrated on a proposed scheme usng varous methodologes. Deductons nferred from the results obtaned are as follows: The transfer operaton has shown by the result obtaned to be dependent on the followng: the unbalance detecton tme (t 1) for an unbalance system; Openng tme (t 2) of the swtch S1 whch s dependent on ts characterstcs; and the commutaton tme (t 3) of the swtch. The trggerng acton accordng to the computer smulatons s dependent on the mode of control-dgtal sgnal processng (a functon of the problem formulaton soluton technque (algorthm). On-lne rearrangement can be acheved wth mnmal servce nterrupton (see Fgure 11 & 12). Manuscrpt receved February 2010, 2436 Copyrght 2007 Prase Worthy Prze S.r.l. - All rghts reserved

13 O.M. Popoola, A. Jmoh, D. Ncolae The computaton analyss of the state of the Feeder was acheved wthout any applcaton of one s ndulgent and judgment (see Fgure 9, 10, 11, and 12). Earler dscussons have establsh the need to mnmze unbalance n the dstrbuton system, however soluton and approaches proposed were desgned to deal wth feeder reconfguraton from the standpont of power loss reducton and load balancng mostly on the medum voltage dstrbuton network; but wth lttle emphases on the method of mplementatons and the technology for mplementaton for the low voltage dstrbuton network. The man am of ths study whch was to propose and research a method and technology for automatcally enhancng the performance of the feeders n the secondary dstrbuton network has been accomplshed. The dea of usng automatc and remote technology based on the open-transton swtchng concept has been mplemented wth great success and shown to be attanable as shown from the results obtaned and deduced n the course of the work. Wth reference to the term of the focus of ths research, the relablty and functonalty of the proposed technque has been demonstrated, tested and found to be adequate. Acknowledgements Ths work was supported by Eskom, South Afrca and Tshwane Unversty of Technology. References [1] A. Jmoh, O. M. Popoola, A.O. Ogunjuygbe, Towards Optmum Performance of a Dstrbuton Feeder, The Internatonal Conference on Electrc Power systems 2007, 23 rd -25 th July, Lagos, Ngera. [2] T, Chen and J. Cherng, Optmal Phase Arrangement of Dstrbuton Connected to a Prmary Feeder for System Unbalance Improvement and Loss Reducton Usng Genetc Algorthms, IEEE Transactons on Power Systems, vol.15 n.3, 2000:pp [3] R. Khordsh, An Effcent Hybrd Evolutonary Algorthm for Mult-Objectve Dstrbuton Feeder Reconfguraton, Internatonal Revew of Electrcal Engneerng, Vol.4 Part B, No.6, pp , Dec [4] G. Sdana, Management of Sub transmsson and Dstrbuton System n Power Utltes. GISdevelopment.net [Onlne]. Avalable from: and %20dstrbuton%20system%20... [Accesses: 21/10/2005]. [5] T. Nknam, R. Khordsh, and B.B. Frouz, A Hybrd Evolutonary Algorthm for Dstrbuton Feeder Reconfguraton, Sadham, Vol. 35, Part 2, Aprl 2010, pp Indan Academy of Scence. [6] K. Huang, H. Chn H, Dstrbuton feeder energy conservaton by usng heurstcs fuzzy approach, Electrcal Power and Energy Systems, vol. 24, 2002: pp [7] J. Teng, C. Chang, A Novel and Fast Three-Phase Load Flow for Unbalanced Radal Dstrbuton Systems, IEEE Transacton on Power Systems, vol. 17 n. 4, 2000, pp [8] S. Mshra and D. Das, A Novel Actve Power Loss Allocaton Scheme for Unbalanced Radal Power Dstrbuton System, Internatonal Revew of Electrcal Engneerng, Vol.3, No.3, pp , June 2008 [9] M.W. St, D.V. Ncolae, A.A. Jmoh, A. Ukl, Reconfguraton and Load Balancng n the LV and MV Dstrbuton Networks for Optmal Performance, IEEE Transactons on Power Delvery, Vol. 22, No. 4, pp , Oct [10] G.R. Regulavalasa, S.R. Annapantula, V.L.N. Sadhu and H.R. Bhanagarapu, A New Algorthm of Dstrbuton Networks Determnng Crtcal Swtches, Internatonal Revew of Electrcal Engneerng, Vol.3, No.2, pp , Aprl 2008 [11] M. Tsay, & S.Chan, Improvement n system unbalance and loss reducton of dstrbuton feeders usng transformer phase rearrangement and load dversty, Electrcal Power and Energy Systems vol.25, [12] A.V. Jouanne, Assessment of Voltage Unbalance, IEEE Transacton on Power delvery,vol. 16 n.4, 2005 pp [13] L.F. Ochoa, R.M. Crc, A. Padlha-Feltrn, G.P. Harrson, Evaluaton of Dstrbuton system losses due to Load unbalance, 15 th Power Systems Computaton Conference (PSCC), vol.6,2005, pp.1-4 [14] M.W. St, A. Jmoh, D. Ncolae, Automatc load balancng n Dstrbuton Feeder, the Industral Electroncs Socety Conference 2005 (IECON 05), Ralegh North Carolne, Unted State of Amerca Date. Ralegh, pp [15] A. Jmoh, M. St, I.E. Davdson, Analyss of Techncal Loss Reducton Optons n Domestc Feeders Usng Engneerng and Economc Model, UIE Internatonal Conference, Jan [16] O.M. Popoola, A.A. Jmoh, D.V. Ncolae, On-Lne Remote and Automatc Swtchng of Consumers Connecton for Optmal Performance of A Dstrbuton Feeder, Internatonal Electrcal Electronc Engneerng Conference (IEEE AFRICON 2007), 26 th 28 th September, 2007 Wndhoek, Namba. [17] R. M. Crc and H. Nour, A New Method for Evaluaton of Dstrbuton System Losses due to Load Unbalance, Internatonal Revew of Electrcal Engneerng, Vol.3, No.1, pp , Feb [18] F. A. Mohamed and H. N. Kovo, Multobjectve Genetc Algorthms for Onlne Management Problem of Mcrogrd, Internatonal Revew of Electrcal Engneerng, Vol.3, No.1, pp , Feb [19] M. Mashour, M. A. Golkar, S. M. Moghaddas-Tafresh, Proft- Based Reconfguraton Methodology for Mult-Feeder Mult- Substaton Dstrbuton Network, Internatonal Revew of Electrcal Engneerng, Vol.5, No.1, part A, pp , Feb [20] NRS 048-2:2004 ELECTRICITY SUPPLY QUALITY OF SUPPLY Part 2: Voltage characterstcs, compatblty levels, lmts and assessment methods Authors nformaton 1 Electrcal Engneerng department, Tshwane Unversty of Technology, Pretora. walepopos@gmal.com 2 Electrcal Engneerng department, Tshwane Unversty of Technology, Pretora. jmohaa@tut.ac.za CORRESPONDING 3 Electrcal Engneerng department, Tshwane Unversty of Technology, emalahlen campus. danaurel@yebo.co.za Olawale Popoola was born n Abeokuta, Ngera n He graduated from Federal Polytechc, Ilaro, Ngera n 1988 wth a Hgher Natonal Dploma (electrcal engneerng), got a bachelor degree (qualty) and a Masters degree (electrcal (power) engneerng) from Tshwane Unversty of Technology n 2005 & 2008 and presently studyng for hs doctoral at the same nsttuton. After graduaton he worked wth Wtt and Bush Shpyard as a Management tranee (Techncal). He later joned Weatherford Internatonal Servces n Ngera as a Jont Analyss Techncan up to Copyrght 2010 Prase Worthy Prze S.r.l. - All rghts reserved Internatonal Revew of Electrcal Engneerng, Vol. 5, n

14 O.M. Popoola, A. Jmoh, D. Ncolae Thereafter he joned J.K Ngera Lmted as Branch Manager (Port Harcourt) overseeng ther ol operaton and drllng servces tll Presently he s Energy Project Engneer at the Centre for Energy and Electrc Power, Tshwane Unversty of Technology. Hs research nterests nclude Energy Management, Renewable and Sustanable energy, and Demand Sde Management, Qualty Management, Specal focus on Contnual Improvement n Learnng Organzaton and Power electroncs applcaton n Power Systems. Mr Popoola s currently a senor member of both South Afrca Insttute of Electrcal Engneers and South Afrca Qualty Insttute n addton to beng a member of South Afrca Assocaton for Energy Effcency. Adsa A. Jmoh (M 86, SM 10) receved the B.Eng. and M.Eng. degrees from Ahmadu Bello Unversty (ABU), Zara, Ngera, n 1977 and 1980, respectvely, and the Ph.D. degree from McMaster Unversty, Hamlton, ON, Canada, n He was wth ABU untl 1992, when he moved to the Research and Development Unt, Natonal Electrc Power Authorty (NEPA), Lagos, Ngera. He was wth NEPA untl 1996 when he moved to the Unversty of Durban-Westvlle, Durban, South Afrca, where he taught courses and carred out research n hghperformance energy effcent electrc machnes and power systems and power electroncs. In 2001, he joned Tshwane Unversty of Technology, Pretora, South Afrca, where, as a Full Professor, he s the Head of Department of Electrcal Engneerng and the leader of the Energy and Industral Power Systems research nche area. Hs research nterests are n electrc machnes, drves, and power-electroncs applcatons n power systems. Dr. Jmoh s a Regstered Engneer n South Afrca. Dan Valentn Ncolae (MIEEE) was born n 1948, n Bucharest, Romana. He graduated the Polytechnc Unversty of Bucharest, Romana n July 1971 wth Msc degree and got hs doctorate degree n 2004 at Vaal Unversty of Technology, South Afrca. After graduaton he worked as researcher n the Insttute for Nuclear Technologes, Natonal Insttute for Scentfc and Technologcal Creatvty - Avoncs Dvson, Bucharest, Romana. In 1998 he joned Tshwane Unversty of Technology, Electrcal Engneerng Department, South Afrca. He s dong research n the feld of power converters, control of electrc machnes and nonconventonal power extracton from hgh voltage transmsson lnes. Dr. Ncolae s a member of Engneerng Counsel of South Afrca and South Afrcan Insttute of Electrcal Engneers. Copyrght 2010 Prase Worthy Prze S.r.l. - All rghts reserved Internatonal Revew of Electrcal Engneerng, Vol. 5, n