VIRTUAL INSTRUMENT FOR CALCULATION OF UNBALANCE FACTORS THROUGHS FORMULAS GIVEN IN INTERNATIONAL STANDARDS AND REGULATIONS

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1 VI FOR CALCUL. OF UNBALANCE FACT. THROUGHS FORM. GIVEN IN INT. STAND. AND REG. VIRTUAL INSTRUMENT FOR CALCULATION OF UNBALANCE FACTORS THROUGHS FORMULAS GIVEN IN INTERNATIONAL STANDARDS AND REGULATIONS Assoc. Prof. Eng. Gabriela RATA PhD 1,Assoc. Prof. Eng. Vasilis CHATZIATHANASIOU PhD 2 Prof.Eng. Valentin POPA PhD, Assoc. Prof. Eng. Mihai RATA PhD 4 1 University Stefan cel Mare from Suceava, 2 University Aristotle, Thessaloniki, University Stefan cel Mare from Suceava, 4 University Stefan cel Mare from Suceava. REZUMAT. Calitatea energiei electrice este o problemă complexă, de mare actualitate în sistemele electroenergetice. Cunoaşterea indicatorilor de calitate ai energiei electrice, metodelor de determinare ale acestora, cunoaşterea limitelorpermiseîn conformitate custandardele, sunt esenţialepentru a asigura o energiede calitate.această lucrareprezintăun instrument virtualde calcul a indicatorilor de regim nesimetric prinformuleleprezentateîn standardeleşi reglementările internaţionale, cu posibilitatea alegerii erii metodei optimede calculaa indicatorilor de regim nesimetric. Cuvinte cheie:calitatea energiei electrice, monitorizare, instrument virtual, standarde ABSTRACT. Power quality is a complex problem, by big actuality in the power systems. Knowledge of power quality indicators, methods for their determination, knowledge of the limits allowed under the standards, are essential to ensure quality energy. This paper presents a virtual instrument for calculation of unbalance factors through formulas given in international standards and regulations. This instrument allow the comparation between different methods for calculating of unbalanced factors and choosing the optimal method. Keywords:power quality,monitoring, virtual instrument, standards 1. INTRODUCTION Power quality is a complex and topical problem of the power systems. Both the consumer and the supplier of electrical energy are interested in power quality monitoring at the point of common coupling (PCC). The realization of quality energy is the responsibility of the suppliers and users ofelectricity [1]. To preserve high power quality, the most important indices,such as harmonics, sags, swells, short interruptions,unbalances and flickers, ideally have to be eliminated. Inrecent years, many researchers have developedtools for accurate power quality analysis [2]. Knowledge of power quality indicators, methods for their determination, knowledge of the limits allowed under the standards, are essential to ensure quality energy. At the establishment of the power quality system of indicators, the following requirements are necessary []: as few, clearly and precisely defined universal enough, to be able to be used in design or operation to enable delimitation of the responsibilities of suppliers and consumers, in power quality perfectibility of power quality indicators, to reflect as fully as many aspects that define power quality defining indicators as statistical parametersfor a sufficient time to obtain authentic information. In most countries, the indicator system of power quality is defined and governed by national rules, more or less consistent with the recommendations of International Electrotechnical Commission. The Institute of Electrical and Electronics Engineersn through its Standards Coordinating Committee 22 coordinates efforts to standardize power quality terminology [4]. This is very important as it allows all parties involved to have common and consistent terms to describe specific power quality. In Romania thereisn t a uniquenormative standard on power quality, some quality indicators are defined and standardized separately in different normatives. Buletinul AGIR nr. /2012 iunie-august 1 15

2 WORLD WORLD ENERGY ENERGY SYSTEM SYSTEM CONFERENCE CONFERENCE WESC - WESC CALCULATING METHODS FOR THE UNBALANCE FACTORS When the voltages of a three-phase system are not identical in magnitude and/or the phase differences between them are not exactly 120 degrees, voltage unbalance occurs [5]. Unbalance voltage and current, lead to impaired of power quality. For unbalance analysis, the method of symmetrical components is mainly applied. This method was introduced in calculations of electric power systems at the beginning of the twentieth century [6]. For one unsymmetrical system of phasors (Y 1, Y 2, Y ) can be determined the symmetrical component set that include: direct sequence, inversesequence and homopolar sequence, acording to the Stokvis-Fortescue theorem: (1) where is the rotational operator, and threephase system of phasors (Y 1, Y 2, Y ) can be relative to the voltages or currents.figure 1 shows the "star" of phase voltages, the triangle of line to line voltages and phasors system of line to-line currents. U 2 2 q 2 I 2 U 2 U I ϕ 2 ϕ q 12 U 1 q 1 U 12 Fig. 1. The phase voltages, line-to-line voltagesand currentsinphasorrepresentation. ϕ 1 I 1 U 1 Re 1 Phase angles q 12, q 2, q 1 between voltage phasors are calculated with the following relations: 2 (2) where φ 1, φ 2, φ, are phases of phase voltages. Line-toline voltages are determined by the relations (): 2, 2, () 2, The unbalance characterization of a multi-phase system is achieved by indicators calculated as reports of negative or zero sequence components, and positive sequence component: - negative unbalance factor 100 % (4) - asymmetry factor 100 % (5) - total unbalance factor % (6) The symmetrical components are calculated strictly on the basis of relations (1), which has the disadvantage that they are complex, with fewer programming language, designed to work in this plan []. In international standard and regulations the relations for determining the unbalance factor for practical use aregiven, being a function of the r.m.s. line or phase voltages. Iterative calculation method Based on relations (1), the modules of symmetrical components are available, that are needed to calculate unbalance factors

3 VI FOR CALCUL. OF UNBALANCE FACT. THROUGHS FORM. GIVEN IN INT. STAND. AND REG The set of relations (7) provides a basis for calculating scalar iterative of symmetrical components. Geometric method The geometric method is based on solving of the triangles (of Napoleon) evidencing construction of symmetrical components. If the homopolar component is nonzero, the following mathematical relationships are obtained with geometric method for calculating the direct and inverse sequence components: where: (7) (8) (9) (10) (11) and (Y 12, Y 2, Y 1 ) is the system of line-to-line voltages or currents. If the homopolar component is zerothe following relationships are obtained for calculating the direct and inverse sequence components: where (15) (16) GOST method This method is proposed by Russian standards [7]. The direct and inverse sequence components (when homopolar component is zero) are: 4 4 (17) (18) Homopolar component calculation is suitable only for phase voltages system: (19) (20) (12) 4 where: (1) (14) Robert-Marquet realationship The mathematical relationship Robert-Marquet gives identical results with the geometric method.by this method, the ratio inverse to direct component is directly calculated: 4 (21) GOST method with error This method suggests simplified calculation relationships that characterize asymmetrical regime but with some error. When the homopolar component is zero, inverse component is: 0.62 (22) Buletinul AGIR nr. /2012 iunie-august 17

4 WORLD WORLD ENERGY ENERGY SYSTEM SYSTEM CONFERENCE CONFERENCE WESC - WESC 2012 where Y max and Y min are the maximum and minimum values ofline-to-line voltages. The homopolar component of phase voltages system is: 0,62 (2) where U fmax and U fmin are the maximum and minimum values ofphase voltages. The error with simplified relations 22 and 2 is approximately ±8%.. THE VIRTUAL INSTRUMENT The emergence of virtual instrumentation is determined the current trend of increasing flexibility of instrumentation, materialized in obtaining by opened architectures, leading to further developments, necessary for a wide range of applications. This is reflected both in hardware and software level, supported by economic benefits [8]. The virtual instruments toghether with intelligent data acquisition systems, represent a rigorous solution, versatile, balanced in terms of hardware-software, for analysis of power quality. A virtual instrument for calculation of unbalance factors through formulas given in international standards and regulationsis described in this chapter. In fact, this virtual instrument allows calculation symmetrical components necessary for determining of unbalance factors. The virtual instrument was realized with the help of the graphicprogramming environment - LabVIEW. This instrument has twoparts: the front panel and the block diagram.from the front panel of the instrument it can be selected the method of symmetrical components calculation. In Figure 2 is presented the front panel of virtual instrument, where is selected iterative calculation method of symmetrical components. Initially the operating conditions balanced are simulated. In Figure and 4 are shownthe resultsobtainedwith geometric method, respectively Gost method with error in the same operating conditions. Whichever method selected on the front panel to calculate symmetrical components, unbalance factors obtained after running the program are in value given by standards (conditions were simulated for the balanced three-phase system). In Figure 5 is ilustrate the block diagram of the virtual instrument where youcan observethe implementationof geometric method (Figure 5 a.) and Gost method with error (Figure 5 b.) The Figures 6, 7, 8 and 9 show the results obtained by iterativ, geometric, Gost and Gost with error method in the simulation of unbalanced operating conditions. Fig. 2. The front panel iterativ calculation method (under balanced operation conditions). 4 18

5 VI FOR CALCUL. OF UNBALANCE FACT. THROUGHS FORM. GIVEN IN INT. STAND. AND REG. Fig.. The front panel geometric method (under balanced operation conditions). Fig. 4. The front panel Gost method with error (under balanced operation conditions). Buletinul AGIR nr. /2012 iunie-august 5 19

6 WORLD WORLD ENERGY ENERGY SYSTEM SYSTEM CONFERENCE CONFERENCE WESC - WESC 2012 a. Y12 Y2 Y1 Y1 Y2 Y b. Fig. 5. The block diagram: a. geometric method, b. Gost method with error 6 20

7 VI FOR CALCUL. OF UNBALANCE FACT. THROUGHS FORM. GIVEN IN INT. STAND. AND REG. Fig. 6. Iterativ calculation method (under unbalanced operation conditions). Fig. 7.Geometric method (under unbalanced operation conditions). Fig. 9. Gost method with error (under unbalanced operation conditions). After running the program, on the front panel we can see that the negative unbalance factor has the same value for the first three methods and is different for the last method. The error that is obtained in simetrical components calculation, respectively in unbalance factors calculation with Gost method with error is 1,5%. It can be observed that under unbalanced operation conditions, the unbalance factors exceedvalues from standards. To see if the unbalance factors calculated by the program exceed the standardised limits, we placed on the front panel one control element that selects this value ( e.g. according to [9] the maximum value must be 2%). When exceeding this value, a warning appears (red button). The here implemented virtual instrument can be used in the evaluation of unbalance in a real network. When unbalance in a real network is evaluated, the measured values for the unbalance factor are compared to its standardized value. It is required that the standardized value not to exceed 95% for the period of observation. 5. CONCLUSIONS Fig. 8. Gost method (under unbalanced operation conditions) Knowledge of power quality indicators, methods for their determination, knowledge of the limits allowed under the standards, are essential to ensure quality energy. In this paper was presented a virtual instrument for calculation of unbalance factors through formulas given in international standards and regulations. The usage of this virtual instrument offers the next advantages: Buletinul AGIR nr. /2012 iunie-august 7 21

8 WORLD WORLD ENERGY ENERGY SYSTEM SYSTEM CONFERENCE CONFERENCE WESC - WESC 2012 simulation of balanced and unbalancedoperating conditions; implementation of methods given in international standards and regulations for calculating the symmetrical componentsand unbalance factors friendly graphic interface is a versatile solution, extensible, balanced in terms of hardware-software report obtaining results in a short time. ACKNOWLEDGMENT This paper was supported by the project "Progress and development through post-doctoral research and innovation in engineering and applied sciences PRiDE - Contract no. POSDRU/89/1.5/S/5708", project cofundedfrom European Social Fund through Sectorial Operational Program Human Resources BIBLIOGRAPHY [1] Sankaran, C., Power Quality, CRC PRESS, ISBN , [2] Knezevic, J. M., Katic, V. A., The Hybrid Method for Online Harmonic Analysis, Advances in Electrical and Computer Engineering, Volume 11, Issue, Year 2011, On page(s): 29 4, ISSN: , e-issn: [] Maier, V., Pavel, S., Maier, C.D., Ingineria calitatii si protectia mediului, U.T.PRESS, Cluj-Napoca, [4] Santoso, S., Beary, H.W.,s.a., Electrical Power Systems Quality, McGraw-Hill, ISBN, X, [5] Fuchs, E.,s.a., Power Quality in Power Systems and Electrical Machines, Academic Press, ISBN , [6] Baggini, A.,Handbook of Power Quality, Wiley, ISBN , [7] *** Gost , Russian Standard, Normy kaczestwa elektriczeskoj energii w sistemach elektrosnabzeniaobszczego naznaczenia. [8] Foșalău, C.; Introducereîn instrumentația virtuală, Editura Cermi Iași, ISBN , [9] ***Normativul PE 14/2001. About the authors Assoc. Prof. Eng. Gabriela RATA, PhD Stefan cel Mare University of Suceava gabrielar@eed.usv.ro Graduated from the Electrotechnical Engineering Department at Gheorghe Assachi University of Iasi, Romania. She is currently Associat Professor at Electrical Engineering and Computer Science Faculty, at University Stefan cel Mare from Suceava. Her areas of interest include power quality of electrical energy, electrical mesurements, sensors and transducers. Assistant. Prof. Eng. Vasilis CHATZIATHANASIOU, PhD. Aristotle University of Thessaloniki, Greece hatziath@eng.auth.gr Graduated from the Electrical & Computer Engineering Department at Aristotle University of Thessaloniki, Greece, where he is currently Assistant Professor. His areas of interest include analysis of coupled magneto-thermal fields in power systems, underground cables and electrical machines operational parameters, thermography and thermal behavior of integrated inductors. Prof. Eng. Valentin POPA, PhD Stefan cel MareUniversity of Suceava valentin@eed.usv.ro Graduated from the Faculty of Electronics, Telecommunications and Information Technology at the "Gheorghe Asachi" Technical University of Iasi.He currently holds a position as Rector of the Stefan cel Mare University from Suceava. His research topic is application in radio frequency identification (RFID) domain. Assoc. Prof. Eng. Mihai RATA, PhD Stefan cel Mare University of Suceava mihair@eed.usv.ro Graduated at the "Gheorghe Asachi" Technical University of Iasi, Electrotechnical Faculty. After finishing of the university he started to work at the Stefan cel Mare University of Suceava, Electrical Engineering Faculty, Electrotechnical Department. His research topicsarepower electronics, digital control of electrical drives and applications of PLC. 8 22