ejsrArmonicos.pdf

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European Journal of Scientific ResearchISSN 1450-216X Vol.27 No.3 (2009), pp.392-399 EuroJournals Publishing, Inc. 2009http://www.eurojournals.com/ejsr.htm

Compensation Capacitors Effect on Harmonics Distribution inElectrical Networks

Hamoudi MoncefDepartment of Electrical Engineering, Faculty of Sciences Engineering

University of Annaba; B.P. 12, 23000, AlgeriaE-mail: [email protected]

Labar HocineDepartment of Electrical Engineering, Faculty of Sciences Engineering

University of Annaba; B.P. 12, 23000, Algeria

Abstract

The problem of controlling power quality is becoming more relevant because of thewidespread use of non-linear and time-varying single-phase or three-phase loads thatincreasingly affect the operation of distribution networks in residential, commercial andindustrial areas. Power quality deterioration is due to harmonic distortion, unbalance,flicker.. Among these issues, harmonics are investigated more accurately in this article.

The classical techniques for studying harmonic propagation consider only the basiccomponents. So this work takes into account the interactions among them through theelectrical network, witch causes harmonic Load Flow

Keywords: Harmonics; power quality; no linear load; compensation; electrical networks.

1. IntroductionPower system harmonics are defined as sinusoidal voltages and currents for each harmonic frequencythat are integer and multiple of fundamental frequency [1]. The rationale is to maintain a globalacceptable electromagnetic environment that coordinates the setting of emission and immunity limits[2]. This is achieved using reference levels of electromagnetic disturbance (electromagneticcompatibility) [9]. So all equipment intended to operate in such environment are required to haveimmunity at least at the margin limits recommended by the international norms [5,6] (European ,

American or else)This limit depends also on the concept of planning level in order to coordinate those limits withthe limits adopted for equipment intended to be connected to the power system [3]. Again, the planninglevel is generally lower than the compatibility level, takes into count the structure and electricalcharacteristics of the considered network [4]. This margin is necessary to make allowance for possiblesystem resonance and for an upward in the level on the network due to future connected loads. Suchloads include computers and other electronics equipments as the adjusted speed motors or all switchedmode power supplies [7,8]

In order to describe harmonics features we study first a simplified circuit fig.1


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Compensation Capacitors Effect on Harmonics Distribution in Electrical Networks 393

Figure 1: No linear load

VS VA

Source Load

Under non linear condition the load voltage VA can be replaced by the three componentsderived from Fourier transformation [10].

1 0A A Ah Av v v v= + + Where:

1 1 12 sin( )A Av V t = +

Is the fundamental component

2

2 sin( )n

Ah Ah hh

v V h t =

= +

Is the harmonic voltage

And

0

0

1T

A A DCv v dt VT

= = Is the dc voltageThe most common harmonic index, which relates to the voltage waveform, is the THD, defined

as:

2

2

1

100%

n

Ahh

V

A

V

THDV

==

Where Vn is the single frequency RMS voltage at harmonic n , and V1 is the fundamental lineto neutral RMS voltage.The waveform distortion can also affect the supplied power. So in order to define another

power quality index, one can divide the apparent power into three orthogonal components [11,12].The active power generated by the feeder is

1 1 1cos( )SP VI = In matrix form the total transmitted power to load can be written as follow

[ ]

^

1

^

2

1 2 ^

^

.. .

.

A

A

S A A Ah An

Ah

An

i

i

P v v v vi

i

=

So the power supplied to the load can be simplified as

1 0A A Ah AP P P P= + + Where

1 1 1 1 1cos( )A A AP V I =


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394 Hamoudi Moncef and Labar Hocine

Is the fundamental component of the power.

2

sin( )n

Ah Ah h h hh

P V I =

=

Is the harmonics powerAnd

0 0A DCP V I= Is the dc power

2. Studied ModelTo show the effect propagation of harmonics in the electrical networks we propose a transmission linemodel Fig.2 in witch the principal feeder supply two types of loads one linear and the other nonlinear,separating by an AC link

Figure 2: Simulation model

Un=30 KV S=(2,5+j1)MVA3 2 1 0,02%

Scc=350 MVA Scc=150 MVAQc Pdc=0,5 W

3. Simulation Results and Analysis:After simulating the proposed model for different capacitors compensation, we can note, that theflowing reactive and active power (fig.3,4) dont take a linear variation, according to increasingcompensation, this is due to harmonics interactions characterized by the distorted power D.


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Figure 3: Active power lines for different reactive power compensation

a/ node 1

b/ node 2

c/ node 3


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Figure 4: Reactive power lines for different reactive power compensation

a/ node 1

b/ node 2

c/ node 3

The placement of compensation capacitors occur resonance with the electrical networkbranches. For example, for Qc=0,2 MVAR it can seen series resonance, causing a magnification ofTHDV at measurement nodes 1 & 2 (fig.5,6). but at Qc=0,4 MVAR it can seen a parallel resonance,

causing a magnification of THDV at node 2 and an attenuation of THDI flowing the branch (1-2)(fig.5,6).


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Figure 5: Total Harmonic Distortion of voltage nodes for different reactive power compensation

a/ node 1

b/ node 2 & 3


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Figure 6: Total Harmonic Distortion of current lines for different reactive power compensation

a/ node 1

b/ node 2

c/ node 3

4. ConclusionOne of the important power quality is the harmonics continents, identified as THD. So with the greatdevelopment of semiconductors the nonlinear loads grow continuously and the particularity of thesetypes of loads is the worst waveform of its current consumption.Because of the voltage loss, feeder implies compensation in order to reduce the power flow. Our workdeal to the following recommendations:

Before implementation of compensation capacitors in the electrical networks, one mast make acare attention in the choice of capacitors size and placement, because it can causes series or/andparallel resonance between the network branches and the compensator for an existing harmonic.


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With harmonics consideration the power factor (pf) dont follow a linear profile for differentvalues of qc, so d must be taken in a count.

The voltage waveform is less altered then the currents, so in this case of transmission line weprefer improve power quality by the implementation of parallel filter

Because of the relationship of harmonics and the electrical parameters including compensation,every new project must restudy the behaviour of the all network.

References[1] G. Desquilbet, C. Foucher, P. Fauquembergue, Statistical analysis of voltage dips, Notes

EDF, 96NR00 102, 1995.[2] Thierry Deflandre et Philippe Maurs, harmonic: electrical networks , Direction des Etude et

Recherche en France -Edition EYROLLES, 1998.[3] Dhombres, J. et Robert, J. B. Fourier physic- mathematics. Editions Berlin, 1998.[4] E. BETTEGA, J . N. FIORINA, Harmonics: inverter & active compensator, CT n 183, Jan

2000.[5] IEEE STD 519-1992, IEEE Recommended Practices and Requirements for Harmonic Control

in Electrical Power Systems, IEEE 519 working Group. 1992.[6] IEEE STD 1159-1995, IEEE Recommended Practice for Monitoring Electric Power Quality,

1995.[7] M. Grandpierre, B. Trannoy, A static power device to rebalance and compensate reactive

power in three phase network: design and control , IEEE Ind. Appl. Soc. Annual meeting, pp.127-13 5, 1977.

[8] L. Morn, P. D. Ziagas, G. Joos, Three-phase solid-state voltage compensator system , Can.J. Elect. Comp. Eng., vol. 15, no. 1, PP. 27-35, 1990.

[9] Mohamad Alaa Eddin Alali, Contribution on the study of active compensator in low voltageelectrical grid , Doctorate thesis, University of Louis Pasteur, Strasbourg, 2002

[10] H. Akagi, Y . Kanazawa and A. Nabae, Generalized theory of the instantaneous reactivepower in three-phase circuits, Proceeding 1983 International power electronics conference.

Tokyo, Japan, PP. 1375-13 86, 1983.[11] M.A.E. Alali, S. Saadate, Y .A. Chapuis, F. Braun, Energetic study of a shunt active

conditioner compensating current harmonics, power factor and unbalanced, EPE-PEMC 2000,Kosic, Slovak Republic, vol. 5, pp. 211-216, September 2000.

[12] L. H. Tey, P. L. So and Y. C. Chu, an improvement of power quality using adaptive shuntactive filter , IEEE Trans. Power Delivery, vol. 20, no. 2, pp. 1558-1568, 2005.

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