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Cf25485491

  1. 1. Purushothama Rao Nasini, Narender Reddy Narra, Santosh A / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.485-491 Modeling And Harmonic Analysis Of Domestic/Industrial Loads Purushothama Rao Nasini, Narender Reddy Narra and Santosh AAbstract This paper discusses the modeling of distortion is caused. The voltage distortion caused bynonlinear electrical loads used in domestic and the harmonic-producing load is a function of both thesmall scale industrial distribution systems. system impedance and the amount of harmonicHarmonic analysis of the distribution system is current injected. The mere fact that a given loadessential to study the behavior of equipments current is distorted does not always mean there willconnected in the non-sinusoidal system be undue adverse effects on other power consumers.environment for designing and optimal location of If the system impedance is low, the voltage distortionfilters. Simulation models are developed for is usually negligible in the absence of harmonicvarious nonlinear loads based on practical resonance. However, if harmonic resonance prevails,waveforms of voltage and current obtained in the intolerable harmonic voltage and currents are likelylaboratory. Analysis of voltage and current to result.harmonics is performed for these loadsindividually. These models are used for harmonic Harmonic currents cause additional lineanalysis of typical domestic and industrial loads. losses and stray losses in transformers. WatthourValidation of the load models is done by meter error is often a concern. At harmonicperforming case study for an industrial supply frequencies, the meter may register high or lowsystem and comparing the THDs obtained from depending on the harmonics present and the responsesimulation using PSCAD/EMTDC package with of the meter to these harmonics. The problems causedthe THD values obtained by measurement. by harmonic currents are overloading of neutrals, overheating of transformers, nuisance tripping ofIndex Terms-- Current harmonics, industrial circuit breakers, over stressing of power factorsystem, nonlinear load, Total Harmonic Distortion. correction capacitors and skin effects. Analysis is commonly done to predictI. INTRODUCTION distortion levels for addition of a new harmonic It is the objective of the electric utility to producing load or capacitor bank. The generalsupply its customers with a sinusoidal voltage of procedure is to first develop a model that canfairly constant magnitude and frequency. The accurately simulate the harmonic response of thegenerators that produce the electric power generate a present system and then to add a model of the newvery close approximation to a sinusoidal signal. addition.However, there are loads and devices on the system The objective of this paper is to consider thewhich have nonlinear characteristics and result in effect of nonlinear loads ranging from adjustableharmonic distortion of both the voltage and current speed drives, to house hold appliances, such as Fanssignals. As more nonlinear loads are introduced with Electronic Regulators on the utility voltage andwithin a facility, these waveforms get more distorted. current harmonics. Some of the commonly used loads The planning, design, and operation of in the domestic and industrial systems are modeled inindustrial and commercial power systems require PSCAD/ EMTDC, by considering the voltage andseveral studies to assist in the evaluation of the initial current waveforms obtained during laboratoryand future system performance, system reliability, experiments. Harmonic analysis of an industrialsafety, and the ability to grow with production and/or distribution system is performed.operating requirements. The studies most likely to beneeded are load flow studies, cable ampacity studies, II.MODELLING OFshort-circuit studies, coordination studies, stability DOMESTIC/INDUSTRIAL LOADSstudies, and routine motor-starting studies. Additional Modeling of household appliancesstudies relating to switching transients, reliability, Nonlinear loads used in industries introducegrounding, harmonics, and special motor-starting current harmonics at the utility. This causesconsiderations may also be required. The engineer in malfunctioning of the sensitive loads connected at thecharge of system design must decide which studies PCC. Hence harmonic analysis of the nonlinear loadsare needed to ensure that the system will operate is essential. Computer simulation is the mostsafely, economically, and efficiently over the convenient way of harmonic analysis provided thatexpected life of the system. the system components are modeled accurately and A harmonic-producing load can affect the verified either through measurements orneighboring sensitive loads if significant voltage mathematically. This section presents the simulation 485 | P a g e
  2. 2. Purushothama Rao Nasini, Narender Reddy Narra, Santosh A / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.485-491models for some of the commonly used industrial In black and white TV receivers, non-loads. This can be used for estimating the harmonic regulated full-wave rectifiers produce a DC voltagecurrents injected at PCC by an industry. which is directly proportional to the peak value of the The current and voltages of the industrial input voltage, so the DC voltages can vary if aloads are nonsinusoidal due to their nonlinear harmonic is superimposed on the fundamentalcharacteristics. Laboratory experimentations were voltages. The resultant effect consists of a lightperformed on the nonlinear loads listed in Table I. variation in the picture and its luminosity. TheAll the loads are supplied from 230 V, 50 Hz ac variations seem to be proportional to the average ofsystem. The supply voltage and current waveforms, the relative variations of the voltages amplitude.and the instantaneous values are recorded using In this case, it will be the arithmetic sum thatTektronix TDS 3032B, 300 MHz digital storage will come into play. Such variations are of nooscilloscope. Harmonic spectrum for each load is importance with harmonics of constant amplitude.also recorded and THDs are calculated for analyzing The color TV sets seem to be less sensitive becausethe effect of harmonics introduced by these loads. they are equipped with voltage stabilizers.Based on these parameters simulation models aredesigned for every load and their combined effect isstudied. This section presents the practically recordedwaveforms for some of the loads and their simulationmodels in PSCAD/EMTDC.TABLE I RATINGS OF DOMESTIC ANDINDUSTRIAL LOADS MODELLED IN PSCAD Fig. 2: Current and voltage wave forms of TV Fig. 3: Practical supply current waveformA) TV and Computer Monitors Computers and T.V sets are modeled by thefronted end power supply consisting of single phasecapacitor filtered bridge rectifier as shown in belowfigure. These loads are rich in harmonics andgenerally produced a pulse waveform with THDInearly 100%.Figure 1: TV modeling in PSCAD/EMTDC For radio receivers established in its time todefine limits for the voltage of the remote controlledcentrals in the network, is also valid for individualharmonics, indeed even for 2 or 3 harmonics. Fig. 4: FFT analysis 486 | P a g e
  3. 3. Purushothama Rao Nasini, Narender Reddy Narra, Santosh A / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.485-491B) Battery Charger Taking for an example in figure, a simplebattery charger circuit with an ac source of 230V 50Hz frequency, an ideal diode connected in series witha 5W resistor and a 12V dc battery. To explain theoperation of the above schematic based on electricalunderstanding, the ac source will give out asinusoidal waveform of 230V with 50Hz frequencyfrom the voltmeter, Vin. Whereas, the voltmeter (Vd )will be a half rectified waveform. The current Iload flowing across the resistorto the load will be equal to the current after the diode.And finally, Vload will be a dc voltage 12V above thezero crossing line because the battery will alwayscarry a 12V dc voltage. To confirm that PSCADgives an accurate graphical result, graphs wereplotted below to show that the above explanation fitswithin the simulated waveform and theoretical Fig. 7: FFT analysisunderstanding of the simple battery charger circuit infigure 12V, 3A. Harmonic analysis of a house load Let us consider in a town, a person having all types of electronic and electrical home appliances, he is the first person to generate harmonics in to distribution system. The amounts of THD produced by him on distribution system are analyzed by using PSCAD/EMTDC simulation. The obtained results are shown in below figure.Fig. 5: Simulation of 12V, 3A, Battery charger inPSCAD/EMTDCFig. 6: Current and voltage wave forms Fig. 8:PSCAD/EMTDC Simulation of Single Home Fig. 9: Home Voltage and current wave forms 487 | P a g e
  4. 4. Purushothama Rao Nasini, Narender Reddy Narra, Santosh A / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.485-491 Where: CFL – Compact fluorescent lamp TV – Television set PC – Personal computer BC – Battery charger AC – Air conditioner RG – Refrigerator WM – Washing machine CD – Cloths dryer OV – electric oven WP – Water lifting pump HW – Electric hot water system If total houses are distributed like given figureFig. 10: Home FFT analysis for Voltage and Current Figure. 12: Houses distribution in Village1Conclusion: When all above loads discussed loads are inswitched on total harmonic distortions of bothvoltage and current (THDI & THDV) are with in thelimits. So no need of using a filter, if a person havingabove rated loads in his house.III.Domestic Load Modeling inPSCAD/EMTDC In small residential system having three Fig. 13: Current and Voltage wave forms of Village1villages. 33kV/11kV substations supply the power tothose villages. Among those village1 is the mostsources for harmonic generation. The people who areliving in other villages are labors; now a day alsothey are using incandescent bulbs. These bulbs arenot that much sources of harmonics. Nobody canusing some costliest equipments like AC, HWS,Oven, Washing machine and dryer etc. So these twovillages are less sources of producing harmonics.Fig. 11: Domestic load modeling in PSCAD/EMTDC Fig. 14: FFT analysis of Village1 488 | P a g e
  5. 5. Purushothama Rao Nasini, Narender Reddy Narra, Santosh A / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.485-491Conclusion: were in place, it is very likely that there is no Village-1 drawing nearly 70A rms value of adequate data available.current. THDI is with in the limit but THDV more Fortunately, extensive sensitivity studies, asthan its limit so we need a filter to reduce voltage described later, show that there is little need to modelharmonics. Series active filter can reduce the those the current source as a harmonic source. Namely, theharmonics. inverter harmonics are negligible as seen from the converter AC side. This is because, in the case ofHarmonic Analysis of a Typical Small Scale PWM and VSI type ASDs, the inverter harmonics areIndustry largely bypassed by the DC link capacitor before they can penetrate into the supply system side. In the case of CSI type ASD, the series inductor serves as a large impedance to block inverter harmonics from ever getting into the converter. Fig. 16: Simulation of ASD in PSCAD/EMTDC Input data needed to construct the above model are as follows:Fig. 15: Simulation of Typical small scale industry in 1) The firing angle of the converterPSCAD/EMTDC thyristors α, Normally in any small scale industry having 2) The direct current flowing into theASD, lift motors, drives, arc welders, fans, inverter Idc,Cycloconverter, personal computers, air conditioners 3) The DC link R and C componentand fluorescent lamps. All those loads are simulated parameters.by using PSCAD/EMTDC are shown in fig 15. The firing angle of PWM type ASDs is always zero. For VSI and CSI type ASDs, the angleA) ASD Modeling increases with the AC motor speed (or inverter There are two mechanisms through which an frequency). The purpose is to maintain a constantASD generates harmonic currents. The first ratio of DC voltage to motor frequency. Assumingmechanism is the converter operation which injects that the ratedharmonic currents into the supply system by an ASD frequency is ωr, and the operating frequency ω,electronic switching process. The second mechanism the firing angle can be determined asis the inverter operation. The inverter can introduceadditional ripples into the DC link current. Theseripples in turn can penetrate into the supply system The direct current into inverter can be estimated fromside. The extent and the frequency of inverter-caused the motor load asripples are largely a action of inverter design andmotor parameters. An ASD can therefore berepresented with a generic three-phase bridgeconverter circuit of Figure. A significant feature of Where P is the motor load including losses,this circuit is that the inverter and the motor are Vph is the line to ground voltage of the supply system.collectively modeled as a direct current source. For typical harmonic studies, α and Idc Theoretically speaking, the inverter and should be varied so that the various ASD-motormotor should be represented as a harmonic current operating conditions are investigated. Representationsource. The magnitudes and phase angles should be of the DC link filter is essential for the correctdetermined from the inverter design and motor simulation of ASDs. It is the filter that makes theoperating conditions. Attempts were made in this ASD harmonic current waveforms different fromresearch to develop a procedure that automatically those of the DC drives.determines the harmonic current source. However,the complexity and variety of the inverters make thework extremely difficult. Even if such a procedure 489 | P a g e
  6. 6. Purushothama Rao Nasini, Narender Reddy Narra, Santosh A / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.485-491Fig. 17: Speed control logic for ASDFig. 18: Voltage and Current wave forms Figu. 22: FFT analysis Harmonic Analysis of a Typical Small Scale IndustryFig. 19: FFT analysis of ASD B) Lift MotorFig. 20:Simulation of Lift motor in PSCAD/EMTDC Fig. 23: FFT Analysis of Small Scale IndustryFig. 21: Voltage and Current wave forms 490 | P a g e
  7. 7. Purushothama Rao Nasini, Narender Reddy Narra, Santosh A / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.485-491 [7] “www.pscad.com ” [8] PSCAD/EMTDC Manual, 2006 [9] “Simulation of Harmonic Currents and Voltages Due to Power Electronic Equipments”; Shahlan b.Fadel [10] “IEEE Recommended Practice for Electric Power Distribution for Industrial Plants”, IEEE Std 141-1993 (Revision of IEEE Std 141-Fig. 24: Voltage and Current wave forms of small 1986)scale Industry [11] “IEEE Recommended Practices and Requirements for Harmonic Control inConclusion: Electrical Power Systems” IEEE After completion FFT analysis of small SM 519-1992, Published by the Institute ofscale industry both THDI and THDV values are Electrical and Electronics Engineers, Inc.,crossing their limits. So the owner of that industry 345 East 47th Street, New York, NY l0017must be use filters to mitigate harmonics other wise USA. April 12, 1993.he may pace sever problems with those harmonics. [12] IEEE Working Group on Power System harmonics, “Power System Harmonics: AnIV.CONCLUSIONS Overview.” This paper discusses the modeling of in IEEE Trans. on Power Apparatus andnonlinear electrical loads used in domestic and small Systems, Volume PAS-102, No. 8, PP.2455-scale industrial distribution systems.In this some of 2459, August 1983.domestic loads such as TV/CPU, Battery Charger are [13] “Influence of Voltage and Currentmodeled and simulated by using PSCAD/EMTDC. Harmonics on Behavior of Electric Devices”Simulated results are sown and Small scale industry Dr. Mike Mehrdad and Dr. E.K.Stanek andloads such as ASD, Lift motor are simulated in Dr. A.S. Jannati.PSCAD/EMTDC. [14] “Effectiveness of different filtering methodologies in Harmonic distortionREFERENCES mitigation” El-Saadany, E.F.; Electrical and [1] “Implementation of Different Passive Filter Computer Engineering, 2001. Canadian Designs for Harmonic Mitigation”; S.N. AL. Conference on 13-16 May 2001 Volume Yousif, M. Z. C. A. Mohamed; National 2, Page(s):1035 - 1040 vol.2. Power & Energy Conference 2004 Proceedings. BIOGRAPHY [2] “Reduction of Voltage and Current Distortions in Distribution Systems with Non Linear Loads using Hybrid Passive Purushothama Rao Nasini, II-M.Tech P.E, Filters”; E.F.El-Saadany; M.M.A. Salama; Department of EEE, SV Engineering College, A.Y. Chikhani; IEE Proceedings- Suryapet. Generation, Transmission and Distribution , Volume 145, No 3, May 1998. [3] “Implementation of Different Mitigation Techniques for Reducing Harmonic Narender Reddy Narra, Assistant Professor in Distortions in Medium Voltage Industrial Department of EEE, SV Engineering College, Distribution System”; T.K. Abdel-Galil, Suryapet. E.F. EI-saadany and M.M.A. Salama. 2001 IEEE [4] “Algorithm for the parameters of double tuned filter”; Harmonics and Quality of Power, 1998. Proceedings. Volume 1, PP. 154-157, 1998; Xiao Yao [5] “Harmonic Analysis for Industrial Power Santosh A, II-M.Tech P.E, Department of Systems Computation Techniques and EEE, SV Engineering College, Suryapet. Filtering”. Ali Moshref Shoaib Khan, St. Bruno. [6] “Understanding Power System Harmonics”; IEEE Power Engineering Review, November 2001 W.Mack Grady, Surya Santoso. 491 | P a g e

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