Impact of the Reactive Power Compensation on Harmonic Distortion Level

Transcription

1 pact of the Reactive Power Copensation on Haronic Distortion Level J. A. M. eto,. C. Jesus, L. L. Piesanti Departaento de Tecnologia Universidade Regional do oroeste do Estado do Rio Grande do Sul juí - RS, Brasil joao@unijui.tche.br Abstract - The goal of this paper is to present a study about the ipact of the application of 2 capacitors banks in substitution of one only bank on 2 (k) utility syste on the voltage distortion level. This analysis was based in the results obtained fro easureents ade with a Power Quality Analyser (P.Q.A) and in siulation results using the PSCAD/EMTDC coputer progra which is a powerful tool for power syste siulation.. DESCRTO OF THE ETWORK For deterination of the voltage distortion in a certain network node the following data are required: contents of forcing of haronics currents source; syste ipedances for particular haronics. The general schee of the two 2 (k) systes configurations analysed are shown in Fig.. Keywords: Power Quality, Haronic Distortion, Measureents, PSCAD/EMTDC, Standards. TRODUCTO Shunt capacitors banks have been installed on distribution feeders to supply the type of reactive power or current to counteract the out-of-phase coponent of current required by the inductive loads. However their application can lead to Power Quality probles which need to be addressed. Short tie ago, the ain concern of the electric utilities was to look for the for of assisting the deand of energy required by the arket, based on assisting basic approaches of quality, that eans, to verify the agnitude and frequency of the supplied voltage. owadays, it should consider several factors related to the power quality proble []. Taking advantage of the proposal to change a bank of.8 MAr existent in the substation (bus 0), for the other 2 capacitors banks which would be installed along the syste in subject, a study was placed to verify the ipact of this substitution on haronic distortion level in this network. The ain idea is to analyze the proble of haronic distortion based on a ethodology that used obtained data fro easureents at buses of the distribution syste, to odel a syste with realistic data and to accoplish coparisons with the results obtained in PSCAD/EMTDC software. This way, easureents were accoplished in different foreseen points of the network, before and after the installation of the capacitors banks, where was possible to accoplish a coparative investigation of the effects of the installation of these capacitors banks on haronic distortion levels. The considerations about the situation of the haronic distortion level were based on EEE Standard 9, 992 as showed in [2]. Fig. A. Syste with only one bank Fig. B. Syste with distributed banks Fig.. One-line diagra of distribution network The fedder was not included in the analysis because it supplies another utility. The power of the capacitors banks and distribution trasforers of the buses fro Fig are showed in Table. The distribution transforers ipedances data are presented in Table 2.

2 Table. Power of Capacitor Banks and Distribution Transforers of each point Bus Capacitor Banks (kar) Distribution Transforers (MA) Table 2. Distribution Transforers rated characteristics Power (MA) Z (%) R (%) (%) OLTAGE HARMOCS The power transforer, in the substation, has the following paraeters: Y GROUDED ( P) / Y ( S) / delta( T ), rated 2 MA GROUDED Short-circuit reactances (priary P, secondary S, and tertiary T): PS = PT ST 8.0 (%) = 4.02 (%) =.69 (%) Point of Coon Coupling (PCC) - this is the location where the haronic currents are evaluated. t will probably be deterined by the utility. Likely locations are the etering point or the high side of the custoer step down transforers []. n this case, all the high sides of the step down distribution transforers.. EPERMETAL RESULTS The field tests which were carried out, had been planned in order to verify the correspondence of the easured distortion haronic and coputed by siulation. The points for the accoplishent of the easureents were selected by the proxiity of the bus foreseen for the installation of the capacitors banks. n order to deterine the network haronic distortion the easureents were done in the secondary of these transforers. All the experiental tests were accoplished during the period of the afternoon and orning with the syste operating. as usual. A. etwork configuration with only one capacitor bank Figures 2,, 4, and show the easureents carried out at soe buses. The inforations about Figures 2,, 4 and are showed in Table. Table shows the suary of onitoring results obtained in all the buses of the network in Fig. A. Thd Hz CHA olts Fig.. oltage haronic spectru on bus 2 OLTAGE HARMOCS Thd Hz CHA olts.0 2. Fig. 4. oltage haronic spectru on bus OLTAGE HARMOCS Thd Hz CHA olts Fig.. oltage haronic spectru on bus 9 Table. Measureents data Bus Total RMS (olts) Fund. (H) RMS (olts) Total Haronic dist.(%) B. etwork configuration with 2 capacitor banks Figures 6,, 8, and 9 show the easureents carried out at the sae buses as the other case. The inforations about Figures 6,, 8 and 9 are showed in Table 4. Table 6 lists the suary of results in all the buses of the network in Fig. B..0 OLTAGE HARMOCS.0 OLTAGE HARMOCS Thd Hz CHA olts Fig. 2. oltage haronic spectru on bus 0 Thd Hz CHA olts Fig. 6. oltage haronic spectru at bus 0

3 .0 2. OLTAGE HARMOCS needs a third haronic, also th and th etc., coponents of current. - haronic currents were odeladed using haronic current injection. The frequency and agnitude of the injected haronic currents was obtained in easureents carried outat the specific buses. Thd Hz CHA olts Fig.. oltage haronic spectru on bus 2.0 OLTAGE HARMOCS 2. Fig. 0A - etwork with only one bank at bus 0 Thd Hz CHA olts Fig. 8. oltage haronic spectru on bus.0 OLTAGE HARMOCS 2. Thd Hz CHA olts Fig. 9. oltage haronic spectru on bus 9 Table 4. Measureents data Bus Total RMS (olts) Fund. (H) RMS (olts) Total Haronic dist.(%) Fig.0B - etwork with distributed banks Fig. 0. The power syste considered A. Transfoer Modeling n this paper, the transfoers were odeled considering the noral agnetizing curve approxiated as four-linear sections shown in Fig.. The General Transforer Model available in PSCAD was used.. HARMOC SMULATOS The siplified single line diagra of the power syste considered in the following analysis is shown in Fig. 0. The syste was suarized only as substation linked to one of the capacitors instalation points (PCC). Trying to siplify the analysis the substations 2 and weren t considered in the odeled syste, because the short circuit levels in both of the, are a lot inferior of the substation. The systes showed in Fig. 0 were odeled in PSCAD/EMTDC considering the three basic eleents: - 2 (k) siilar network of the three feeders that assist the studied electric utility syste. The odel coupled P section was used; to represents the buses. - distribution transforer with the siilar characteristics of those connected at buses onitored. This consideration is very iportant because in the detailed syste, the transforers are a iportant source of the lower syste haronics. t is because sinusoidal agnetisation of iron Fig.. oral Magnetizing Curve Where is the instantaneous utual flux link (Wb), is the instantaneous agnetizing current (A). The rated current (A), and the rated flux, can be calculated as follows: S (Wb), = () 2 = dt (2)

4 Where S is the rated power (A), is the rated voltage (). The three basic paraeters required for representing saturation curve in the Saturation Property Sheet for the General Transforer coponent was obtained by as follows fro the data in the oral Magnetizing Curve of the transforers. Winding air core reactance: based on the two highest points. ω AR (p.u.) is deterined 4 AR = = () Z BASE 4 Z BASE Rated agnetizing current: MR (%) is deterined using a point closest to the rated flux. = 00 (4) knee point of the agnetizing curve: deterined based on the highest point. ω KEE (p.u.) is AR Z BASE L AR = () ω KEE = 4 ( L AR 4 ) The choice of the base voltage ust be related to the sae side of the winding of the agnetizing curve that was odeled. The Saturation Property Sheet allows to choose the winding to place the saturation. B. Syte with only one capacitor bank Fig. 2, and, show the siulation results on two points on the distribution transforers low voltage side (L). The siulation results on distribution transforers high voltage side (PCC or H) are represented by Fig. 4 and. The considered haronic currents were those showed in Table 4. Table shows the suary of results obtained in the points of the network in Fig. A on the distribution transforers low voltage side. The results for the PCC are showed in Table 8. (6) Bus Total oltage Distortion THD (%) Min. Med. Max. Table. Monitoring Results Haronic oltages n () Haronic Currents n (A) Bus Total oltage Distortion THD (%) Min. Med. Max. Table 6. Monitoring Results Haronic oltages n () Haronic Currents n (A)

5 Table. Siulation Results on L side - Distribution Transforers Bus () () () () THD (%) Table 8. Siulation Results on H side - Distribution Transforers Bus () () () () THD (%) Fig. 2. Haronic oltages on bus 9 L Fig.. Haronic oltages on bus 68 L Fig. 4. Haronic oltages on bus 9 H Fig.. Haronic oltages on bus 68 H C. Syte with distributed capacitor banks Fig. 6 and, give the siulation results in two points on L. H siulation results are represented by Fig. 8 and 9. The considered haronic currents are shown in Table 6. Table 9 lists the suary of results obtained in the points of the network in Fig. A on low voltage side. The results for the high voltage side (PCC) are shown in Table 0.. COCLUSOS This paper has presented an investigation carried out in thirteen points of a 2 (k) network, it was based on field tests whose data were used on the odeling of a particular reducted syste allowing the haronic analysis of this utility syste. The arisen specific conclusions fro this study could be suarized as follows: Fro the application point of view, this analysis showed that is very difficult to copare experiental with siulation results. However the proposed odeling is pratical and provides good results take in consideration the coplexity of the haronic analysis. Haronic voltage levels deterined through siulations and easureents can be copared in Tables and, and Tables 6 and 9. We have included the loads in bus 0 and PCC obtained in easureents. Established ipedance values of the circuit allow the deterination of the ipact of circuit paraeters changes on voltage distortion levels caused by haronic currents obtained in field tests. This akes the siulations possible of both existing and planned systes. Besides of the benefits usually expected with the optization of the reactive power flow, the distortion voltage level has presented an iproveent as can be verified fro the obtained results in the easureents and also in the siulations. n all of the points of coon coupling (PCC) analysed the harnonic distortion levels atept the deand of the EEE Standard 9, 992, in ters of voltage and current, showing that the substitution of the capacitor banks were profitable, considering the ipact on power quality focusing haronic concerns. The transforers odeling was realized based on noral agnetizing curves and rated current of each.

6 The saturation curves were adjusted to give a better fit, by changing KEE and AR because was considered that transforers were responsible for part of the haronics.. ACKOWLEDMETS The authors gratefully acknowledge to DEME - Departaento Municipal de Energia de juí technical staff, Mr. Sandro Studt, Mr. Luciano Malaquias and Mr. Diego Morais. They wish to express their gratitude to Mr. Edson L. Batista for his cooperation on field tests.. REFERECES [] T. E. Grebe, Aplication of Distribution Syste Capacitor Banks and Their pact on Power Quality, EEE Transactions on ndustry Applications, vol. 2, O., May /June 996, pp [2] T. S. Key, J. S. Lai, Coparison of Standards and Power Suplly Design Options for Liiting Haronic Distortion in Power Systes, EEE Transactions on ndustry Applications, vol. 29, O. 4, July/August 99, pp [] W. C. Feaster, E. L. Harder, Syste Lower- Haronic oltages Methods of Calculation and Control by Capacitors, AEE Transactions, vol. 60, 94, pp [4] K. Hilava, et al, Experiental nvestigation of Haronics pedances and Other Electrical Paraeters of High oltage etwork, Proceedings of the 986 nternational Conference on Large High oltage Electric Systes, 2th August 4th Septeber, Paris. [] R. C. Dugan, et al, Electrical Power Systes Quality ", McGraw-Hill, ew York, 996. [6] H. Doel, Transforer Model in the Siulation of Electroagnetic Transients, th Power Systes Coputation Conference, England, Sept. -, 9. [] EEE Recoended Practices and Requerients for Haronic Control in Electric Power Systes, EEE Standard 9, 992. Table 9. Siulation Results on L- Distribution Transforers Bus () () () () THD (%) Table 0. Siulation Results on H- Distribution Transforers Bus () () () () THD (%) Fig. 6. Haronic oltages on bus 9 - L Fig.. Haronic oltages on bus 68 - L Fig. 8. Haronic oltages on bus 9 - H Fig. 9. Haronic oltages on bus 68 - H

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