analysis and control of harmonic distortions on electrical distribution ... · harmonic rate of...

International Journal of Scientific & Engineering Research, Volume 4, Issue 7, July-2013 2595 ISSN 2229-5518

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Analysis and Control of Harmonic Distortions on Electrical Distribution Systems in Benin – the

Case of ABOMEY CALAVI NETWORKS .

HOUNDEDAKO Sossou1, DAI TOMETIN Derrick1, CHETANGNY K. Patrice2 ESPANET Christophe2

*Laboratoire d’Electrotechnique, de Télécommunication et d’Informatique Appliquée (LETIA) Ecole Polytechnique d’Abomey-Calavi, Université d’Abomey-Calavi 01 BP 2009 Cotonou, Bénin.

Email: [email protected] **FEMTO-ST Département Energie, Université de Franche-Comté, France.

2, Avenue Jean Moulin 90000 Belfort, France Email: [email protected]

Abstract— The quality of electrical energy is characterized by stability of voltage, current, frequency, active and reactive power, power factor, peak factor and harmonic distortions of the sinusoidal wave forms. The consequences of harmonic distortions of transmitted electrical energy could be damage of condensers, untimely release of circuit breakers, resonance in the networks,

warming of transformers and over-heating of electrical appliances. In this respect, the harmonics on the distribution networks of the Beninese Company of Electrical Energy (SBEE), at Abomey-Calavi were studied to develop techniques for analyzing and

control of the system stability to meet international standards for power transmission. The electrical filter systems of the trans-mission networks were modeled, and simulated by MATLAB Simulink numerical tools to obtain data on levels of harmonic

reduction. The harmonic disturbances caused by the nonlinear loads were reduced by 92.85 %. Also, reduction of the effective current by 18.20 % and apparent power by 18.04 % were achieved, while improvement of the power-factor by 12.65 %, a gain in energy (around 445 kWh), and increase in the capacity (by 18%) of the electrical distribution network of the SBEE were also ob-tained. Therefore, integration of the filters on the networks reduced the harmonics on the electrical energy distribution systems.

Index Terms— energie losses, distribution network, harmonic, non linear loads, power factor, quality of electrical energy, stability of voltage

—————————— ——————————

1 INTRODUCTION

ectifying static inverters have been commonly employed in both industrial plants and domestic applications for the

regulation and control of both direct and alternating currents used in power supplies for computers, televisions, variacs of light, regulators of electric heating and in variable speed transmissions for washing machines, vacuum cleaners, tools, electro-transportable, etc. The use of static inverters in the electrical energy distribution networks considerably improve the system performances and effectiveness. Unfortunately, the inverters in general degrada-tion of the quality of the currents and voltages in the distribu-tion networks. Indeed, the common occurrences of electric disturbances are due to the growing number of non-linear loads imposed on the electric lines, as the loads have the ten-dency to absorb non-sinusoidal currents and thereby intro-duce harmonic distortions on the electric lines [1]. The gener-ated electric current harmonics are propagated throughout the entire distribution networks, can seriously affect operations of equipment, and in some cases, causing serious damage or complete deterioration of equipment and appliances [2].

Research was conducted to develop techniques and solutions for reducing the harmonic distortions on power transmission systems of Beninese Company of Electrical Energy (SBEE), as presented in this paper. The low quality of electrical energy in Benin has become a serious concern [3, 4], and the harmonics have become sources of nuisance in the electrical network; hence, the need for the analysis and control of the harmonics to develop new solutions to reducing the harmonics. In the past, Parallel Active Filters (FAPs) have proven to be effective techniques for the compensation of the harmonic components [2, 5]. The filters identified the harmonic compo-nents and effectively feedback into the electrical network in opposite phase; and were also able to correct the power-factor and compensate for any possible imbalances of any three-phase system. Over the last ten years, many techniques based on networks neuromimetic and Adaline (ADAptive LINear Element) in particular have been developed to identify and filter the harmonics in the electric systems [6]. The identification and analysis of harmonic levels of distor-tions of the SBEE network by series of analyzer measurements,

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choice of filters to regulate and control the electrical network and simulation of the network-filter system with MATLAB Simulink aimed at practical realization for the Commune of Abomey-Calavi are presented in this paper.

2 THEORETICAL ANALYSIS 2.1 Harmonic Distortions The periodic instantaneous voltage and current can be ex-pressed by Fourier series in the form

)sin(2)()( ,11 neffnnn n nwtVtVtV θ+== ∑∑ ∞

=

∞

= (1)

)sin(2)()( ,11 neffnnn n nwtItItI θ+== ∑∑ ∞

=

∞

= (2)

where frequency ω = 2πf, Vn,eff is effective value of the har-monic voltage of row n, In,eff is effective value of the harmon-ic current of row n, and θn is the current phase angle of row n. The corresponding expressions for the effective values of the voltage and current are,

∑∞

==

12,n effneff VV (3)

∑∞

==

12,n effneff II (4)

The distorted average power mode is expressed as

)cos(,1 , nneffnn effn IVP fθ −= ∑∞

= (5)

The harmonic current is taken into account by the apparent power (or distorted power) S,

222 DQPS ++= (6)

where, ϕ n : tension phase angle of row n Q : Reactive power D : Distorted power The power factor modified by the distorted power is;

fff

coscoscos

1,11,1 ≠==== depdiseff

eff

effeff

effeffp FF

II

IVIV

SPF (7)

where eff

effdis I

IF ,1= is the factor of distortion and

is the factor of displacement. The individual voltage or current harmonic distortion is calcu-lated by,

eff

effn

eff

effn

VV

II

H,1

,

,1

, == (8)

while the total voltage harmonic distortion and total current harmonic distortion are given by

eff

n effnVT V

VH

,1

22,

,∑∞

== (9)

eff

n effnIT I

IH

,1

22,

,∑∞

== (10)

2.2. Filter Elements Parameters The filters required for control of harmonics of row 3, 5, 7 pri-marily present on the entire network must operate at standard frequencies of 150 Hz, 250 Hz and 350 Hz, while exhibiting very excellent quality factors in order to minimize the re-sistance of inductors. The values of resistance (R), inductance (L) and capacitance (C) of the elements of the resonance filter circuit were determined in terms of the reactive power filter and factor of quality, as

PfUQ

Cn

C22π

= (11)

CfL 2

021

π= (12)

QfL

R 02π= (13)

where Qc is the reactive power filter (3.5 kVAR), f is frequency of the network (Hz) (50 Hz), fo is agreed frequency of the net-work (Hz) (value), Un is nominal voltage of the power supply of the filter (volts) (400 V), n is the row of harmonics, and Q is the quality factor (75 ). The parameters of the filters were set by the operating Station in accordance with the harmonics to be eliminated. 3. EXPERIMENTAL WORK 3.1. Measurement of Quality of Voltage and Current The quality of the voltage delivered by the SBEE was assumed to be affected initially by harmonic rate of distortion, which was not applicable for the current. The primary reason was that the subscribers in Abomey Calavi were domestics users, with a number of single-phase loads consisting of televisions and other electronics equipment, and the voltage was ob-tained by rectifying single-phase current,. An analyzer for three-phase electrical networks, type CA 8334 (Chauvin Arnoux) of accuracy of 1 %, was used to measure and record directly the elements characteristic of the quality of

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electrical network in Abomey Calavi; in terms of the voltage, current, frequency, active power, reactive power, power-factor, harmonic rate of distortion, peak factor and the sinusoidal alternating wave patterns. The data was analysed by Qualistar View software, and plotted using Excel. 3.2. Electrical Harmonic distortion at Abomey-Calavi (Zoca) The measurements taken at Abomey-Calavi (the second most populated Commune in Benin, next to Cotonou) related to single-phase loads usage from time 2000 to 0500 H daily, and effect of the energy quality on the electronics equipment (such as televisions). The power level of 20 kW was considered not very high, the loads-distribution between the three phases was not balanced in median value, the current in the neutral was important, and a strong harmonic content 3 was obtained. The total rate of distortion of harmonics in voltage was 2.0 %, while that in current was 35.8 %, indicating the existence of major distor-tions of the current which would disturb the stability and quality of the whole of network SBEE. 4. MODELING HARMONIC DISTORTED VOLT-AGES The modeling of the harmonic distorted voltages in the net-work was based on the electric characteristics of the 250 kVA 15/0.4 kV transformer and the electric low tension line of 50 mm2 twisted standard aluminum cable on a linear distance of 1 km Zoca station. The network from the distribution station to subscribers started from HTA/BT transformer (on a linear distance of 1 km of twisted cable standard aluminum of sec-tion 50 mm2) corresponding to a model of the sources distort-ed by pre-existing harmonic voltages. For the purposes of cal-culations, the pre-existing harmonic voltages were regarded as sources of harmonic voltages. 5. SIMULATIONS OF FILTERS TO IMPROVE QUALITY VOLTAGE For improvement of the quality of electrical energy, a filtering system for the SBEE network was simulated using harmonic distortion equations and data obtained by network analysis. The simulation was made on the level of the Post Office of Zoca at Abomey-Calavi. The filters were calculated to reduce harmonics 3, 5 and 7. Simulation was made by using the Matlab software. Generators with 150, 250 and 350 Hz repre-sented the existing harmonics at the station. The amplitude could be adjusted for different measurements.

Simulations were performed for the the distribution net-work circuit with filters integrated and without filters at Zoca distribution station.

5.1. Description of Electric Circuit

Figure 1. Circuit diagram of simulation under Matlab (improve

quality of diagram)

The circuit for the simulation at Zoca (Fig. 1) consisted of a source voltage HTA 15 kV from a generator representing the network upstream, a transformer HTA/BT 15KV/0.41 kV char-acterized by internal impedance and mode of coupling, and a low impedance voltage line of 1 km line of a twisted alumini-um cable of 50 mm2 representing telegraphic connection be-tween the distribution station and the subscribers. A three-phase load circuit RL symbolized the subscribers, for which the maximum loading and the parameters were obtained dur-ing measurements: THDI : 39.6 % THDU : 2.1 % S : 29.32 kVA P : 25.8 kW Q : 13.7 kVAr D : 3.8 kVAr PF (Power Factor): 0.89 DPF (Displacement Power Factor): 0.9 5.2. Simulation Three generators of harmonics, each of row 3, 5 and 7, was a power source of frequency equaled to multiple of the funda-mental one. A set of three passive filters of harmonics of re-spective row 3, 5 and 7 were used to generate the desired harmonic contents, and were selected in accordance with the computed values (30 % for current Harmonic 3, 12 % for row 5 and 3.8% for row 7) and connected to the network by the means of a switch. The switch was either coupled or not to the

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filters on the distorted network for the simulation in the pres-ence or without resonant filters.

The block A served as measure of outputs of the secondary of the distribution transformer of the simulated station. An oscilloscope was used to visualize the various signals of volt-ages and currents to the secondary of the transformer. A unit powergui which is graphical user interface for analysis of cir-cuits and systems and environment block for SimPowerSys-tems models, was used to select the signals to visualize and make parameter settings, and the data obtained after simulation with Matlab/Simulink are shown in Table 2.

6. RESULTS 6.1. Analyzes and interpretation of quality data of Zoca

The curves for the voltages and currents obtained at the Zo-ca distribution station are shown in Figs. 2 (a) and (b).

(a)

(b)

Figure 2: Signals of the electric parameters, (a). Vthd, (b). Ithd at Zoca distribution station Where,

VTHD L1 : Voltage (neutral-phase) distorsion factor of phase L1 VTHD L2: Voltage (neutral-phase) distorsion factor of phase L2 VTHD L3: Voltage (neutral-phase) distorsion factor of phase L3 Athd L1: Current (neutral-phase) distorsion factor of phase L1 Athd L2: Current (neutral-phase) distorsion factor of phase L2 Athd L3: Current (neutral-phase) distorsion factor of phase L3 The curves indicated different levels of the rates of harmonic distortion in voltage and current, as well as on the level of the displacement and power-factors. The total rate of distortion of harmonic in voltage was 2.1 %, that of the current was about 39.6 %. The peak value of the signals of voltage was 1.41 and that of the current reached 1.9. The harmonics of row 3, 5 and 7 were observed. The 39.6 % rate of distortion of current showed the presence of non-linear loads on the network, as confirmed the peak factor of 1.9. Examination of the spectral of the signal of current revealed the presence of harmonics of row 3, 5 and 7 and some traces of rows 9 and 11. The data were obtained with a three-phase network analyzer of “Ar-noux Chauvin” The quality values relating to the voltages were much lower as compared with the case of the currents, which were very high. The values required correction and control to improve the quality of electrical energy and reduction in the rates of losses inter alia, by eliminating or reducing malfunctioning caused in the electrical network by losses of energy and power. 6.2. Filter Parameters The values of capacitance, inductance and resistance required to set up filter circuits to eliminate harmonic rows 3, 5, and 7 are shown in Table 1, as calculated from eqns. (11 and 12). Table 1. Parameters of the filter circuit elements for Zoca sta-tion

6.3. Simulation Outcomes For the simulation without integration of filters in the distribu-tion network, the signal output of the secondary of the trans-former was distorted, and similarly for the current and the

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voltage, which exhibited relatively high rates of distortion. In the simulation with filters integrated into the network, all the quality parameters of the network decreased, as shown in Ta-ble 2. The results in Table 2 indicated correction of the current and voltage signals and consequent improvement of the quality of electrical energy by the integration of the harmonic anti filters on the electrical distribution network. Table 2: Simulation data with or without the use of the filters.

FP : Power factor THD I % : Current Distortion Factor in % THD V % : Voltage Distortion Factor in % I rms (A): rms value of power frequency current (geometrical sum) These values were recorded during our experiments made on site. Fig. 3, 4, and 5 show the simulated outputs for current and voltages without integration of filter circuits in the distribution network.

Figure 3. Current and voltage variations to the secondary of the transformer in absence of the filters (Zoca)

Figure 4. Current signal and spectrum in absence of the filters (Zoca)

Figure 5. Voltage signal and spectrum in absence of the filters (Zoca) The outputs of the simulations whereby the filters anti-harmonics were coupled with the distribution network are shown in Figs. 6, 7 and 8.

Figure 6: The current and voltage signal variations to the sec-

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ondary of the transformer in the presence of filters (Zoca)

Figure 7. The signal and spectrum of the current in the pres-ence of filters (Zoca)

Figure 8. The signal and spectrum of the voltage in the pres-ence of filters By integrating the filters, the harmonic currents decreased; an average reduction of the effective current of about 18.20 %, an average reduction of the harmonic content (THDI) by about 92.5%, an average improvement of the power-factor of about 12.65 %. The corrections provided a gain of about 20 % on av-erage of energy or power in the exploitation of the electrical network of distribution. 7. DISCUSSION The study of the electrical distribution network of Abomey-Calavi and feeder system low voltage indicated the existence of harmonics on the electric distribution network of the Beni-nese Company of Electrical energy. By determining the values of the anti-filter elements (capacitance, inductance and re-

sistance) and integrated into the network, the quality of the supply of electrical energy in the Zoca zone was improved by correction of the often degraded power-factors, and decreased the rate of loss in the distribution network. For the general level of the electrical network, a portion of the 18 % to 20 % of rate of losses recorded on the distribution net-work came from the losses due to the harmonics originating from the subscribers. The elimination of the harmonics after identification on the distribution network would contribute amongst other things to the reduction of the rate of loss. 8. CONCLUSION Upon simulation of installation of harmonic anti filters in the Zoca distribution, an average reduction of the effective current of about 18.20 %, an average reduction of the apparent power of about 18.04 %, an average reduction of the harmonic con-tent (THDI) of about 92.85 %, an average improvement of the power-factor of about 12.65 %, a profit of energy and an in-crease in the capacity of the electrical distribution network of the SBEE were achieved. Considering the performances and advantages of the filters, the results obtained and the economic impact of harmonic stabilization, the installation of appropriate filters would re-duce considerably the harmonics on the electrical energy dis-tribution systems of the Beninese Company of Electrical ener-gy, and minimize the nuisances generated by the nonlinear loads.

REFERENCES [1] Akagi H., "Trends in Active Power Line," IEEE Transactions on

Power Electronics, vol. 9, no. 3, pp. 263-268, 1994 [2] Bruyant N., “Etude et commande généralisées de filtres actifs

parallèles, compensation global ou sélective des harmoniques, régime équilibré ou déséquilibré ». Thèse de doctorat de l'uni-versité de Nantes, France, (1999).

[3] Gouraud T., Auger and F., Guglielmi M., "Recursive estimation of signal in autoregressive noise", Proceedings of ICASSP-95, Detroit, Mai 1995

[4] Gouraud, T., Auger F., Chevrel P., Guglielmi M., Lebert G., et Machmoum M.," Robust and frequency adaptive control design for a single-phase power filter", I. E. E. E. Electrimacs’ 96, Saint-Naziare, 1996, Septembre 1996.

[5] Gouraud T., « Identification et rejet de perturbations harmo-niques dans des réseaux de distribution électrique ». Thèse de doctorat, Nantes, France, 1997.

[6] Ould Abdeslam D. Techniques neuromimétiques pour la com-mande dans les systèmes électriques : application au filtrage ac-tif parallèle dans les réseaux électriques basse tension, Universi-té de Haute Alsace Thèse de doctorat, 195, 2005.

[7] Abdusalam M. M.. Structures et stratégies de commande des filtres actifs parallèle et hybride avec validations expérimen-

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tales. Université Henri Poincaré, Nacy-I. Thèse de doctorat, 187, 2008.

[8] Bernard S., Trochain G.. Compensation des courants harmo-niques générés par les ordinateurs grâce à un compensateur actif d’harmonique révolutionnaire. Edition Merlin Gerin, Lyon France, 2000

[9] Bettega E., Fiorina J-N. Harmoniques, convertisseurs propres et compensateurs actifs. Cahier technique n° 183. Edition Scheider Electric, Grenoble, France, 2004

[10] Bouchard R-P., Olivier G.. Electrotechnique. Presses internatio-nales Polytechnique, Quebec, Canada, 1999

[11] Calvas R. Les perturbations électriques en basse tension. Cahier technique n° 141. Edition Scheider Electric, Grenoble, France, 2001.

[12] Deflandre T., Mauras P.. Les harmoniques sur les réseaux élec-triques. Editions Eyrolles, Paris, 1998

[13] Djeghloud H. Filtrage actif de puissance. Université Mentouri Constantine. Thèse de doctorat, 196, 2007.

[14] Ferracci P. La qualité de l’énergie électrique. Cahier technique n° 199. Edition. Scheider Electric. Grenoble, France, 2001.

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