EFFECTS OF GROUNDING SYSTEM ON POWER QUALITY

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1 EFFECTS OF GROUNDING SYSTEM ON POWER QUALITY Bhagat Sigh Tomar, Dwarka Prasad, Apeksha Naredra Rajput Research Scholar, Electrical Egg. Departmet, Laxmi Devi Istitute of Egg. & Techology, Alwar,(Rajastha),Idia Associate Professor, Electrical Egg. Departmet, Laxmi Devi Istitute OfEgg. & Techology, Alwar,(Rajastha),Idia, Juior Egieer-I,RajasthaRajyaidyutPrasaraigam Limited(RRPNL), Alwar,(Rajastha),Idia Abstract The purpose of this paper is to preset the importace ad affects of groudig ad harmoics to the quality of power. The power quality coditios sigificatly depeds o the every aspect i electrical system such as voltage, curret, frequecy, power, power factor ad so o. As the result of this aalysis, the groudig coditios used i the data ceter was foud to have o sigs of severity i power quality coditios. However, there were some issues of improper wirig ad groudig foud i the systems. O the other had, the harmoic distortio i data ceter was discussed i terms of the source of harmoics effects of harmoic o the performace of data ceter. I order to idetify the cause of such orders of harmoics i this system, the most o liear load is idetified. Therefore, some recommedatios ad mitigatios of the harmoics were discussed. IdexTerms Groudig, Harmoics, Power Quality, data ceter, oltage Levels. I.INTRODUCTION Power quality issues ca be very high-speed evets such as trasiets, harmoic, high frequecy oise, faulty wirig of groudig system, voltage swells ad sags ad total power loss. I this aalysis, groudig ad harmoics will be discussed i terms of power quality. Groudig may ot be II. BASIC ON HARMONICS The basic harmoic theory which accordig to Fourier theorem, periodic o-siusoidal or complex voltage (Figure 2) or curret waveforms ca be represeted by the sum of a series of multiple frequecy terms of varyig magitudes ad phases as show i equatio (1). complicated but whe a lack of uderstadig mixes with folklore ad traditio, it may become exceedigly complex. It has bee reported that 80 to 90% of power quality problems are mostly caused by improper wirig ad groudig. Groudig is defied as a coductig coectio, whether itetioal or uitetioal by which a electric circuit or equipmet is coected to the earth or to some coductig body relatively large that serves i place of the earth. Groudig system desigs ad operatios are completely depeds o the applicatios i particular requiremets. By specializig the groudig techiques ca evolve the complexio of groudig system topic to meet the perceived groudig requiremets of electroic equipmet. The assessmets iclude represetatio of groudig systems with liear ad oliear parameters to produce a better represetatio of the overall electrical system at abormal operatig coditios [1]. Aother power quality issue is harmoic [2]. Harmoic is defied as siusoidal compoet of a periodic waveform havig a frequecy that is a iteger multiple of havig fudametal frequecy. It is also a mathematical model that used to aalyzed distorted waveforms ad ca be geerated by o liear electroic loads[3]. The harmoic related losses reduce system efficiecy, cause apparatus overheatig, ad icrease power ad air coditioig costs. The harmoic currets ca have a sigificat impact o electrical distributio systems ad the facilities they feed. f t) a [ a cos( t q )] (1) ( 0 where: a is the magitude of the th harmoic frequecy a is the d.c. compoet o q is the phase agle of the th frequecy is the fudametal frequecy. =1,2,3, harmoic 49

2 Harmoic is measured usig total harmoic distortio (THD) which is also kow as distortio factor ad ca be applied to curret ad voltage. It is a square-root of sum of all harmoic magitudes over the fudametal. Equatio (2) shows the calculatio for voltage total harmoic distortio (THD v ). THD (2) where: 1 is the magitude of fudametal frequecy voltage. is the magitude of th voltage. harmoic frequecy III. PROBLEM STATEMENT Data ceter today are desiged with systems ad redudacies to miimize the loss of power [4]. However, the importat issue to be emphasized is the quality power. Groudig of the data ceter is oe of the ways to make sure the performace of the data ceter is always maitaied at the acceptable level. Data ceter is dealig with may electroic equipmets that ofte ru ito harmoic issues ad the it should be take care of by mitigatig the harmoics[5]. Supply voltage Distorted oltage waveform No-liear (a) time (b) time Fig. 2 Harmoic Curret ad oltage Distortio Table 1 categories of power quality evets with duratios ad voltage magitude 50

3 I. SOME CASE STUDIES IN POWER QUALITY A.OLTAGE TRANSIENTS CAUSING DIODE FAILURES Eviromet - A plastic extrusio maufacturer i the mid-west had a 480 delta feedig a plastic extrusio machie. The ASD-drive sychroous motor i the extruder had a half-wave bridge rectifier circuit to provide excitatio voltage to the pole coils. Problem -Diodes o the half-wave bridge exciter circuit were blowig out, ad the filters to the SCRs were beig damaged. Moitorig Survey - Three chaels of the voltage supply feedig the extruder were moitored for just two secods before eough data was collected to determie the cause of the failures. A burst of trasiets would occur three times a secod. The RMS voltage did ot chage sigificatly durig these trasiets. Closer examiatio of the waveforms showed that the trasiets were actually a repetitive series of voltage trasiets, occurrig six times a cycle o all three phases. A example of the voltage waveforms for oe phase is show i Figure 1. These repetitive voltage trasiets are referred to as voltage otches. The maximum voltage of the trasiet could produce damage, ad the voltage otches that cross the zero axis could result i zero crossig errors. Closer examiatio of the trasiets is show i Figure 2. Fig. 1 Aalysis Fig. 2. Sigle Trasiet Waveform The followig were calculated values of this voltage disturbace moitorig period: Number of trasiets: 192 Amplitude: -580 volts. Worst Absolute amplitude (from zero crossig): 864. Rise time: microsecods Frequecy (1/4*rise): 230.4kilohertz. Number of zero crossig errors this frame: 146. Worst zero crossig width: microsecods. Worst zero crossig delta voltage: 168 volts. Worst otch area: voltsecods. Trasiet Aalysis The absolute amplitude value cofirmed the cause of the damage to the diodes, as this voltage exceeded the ratigs of the diodes i the half-wave bridge. The very fast rise time ad equivalet frequecy greater tha 100 KHz of the trasiet idicates that the source of the trasiet is relatively close to the measurig poit.this would idicate that the origi of these trasiets was a electroic switchig load such as a bridge rectifier used o may electroic motor drives. The trasiets o other phase voltage chaels were ot the same polarity, but occurred at relatively the same time, as show i Figure 3. Zero crossig errors ca cause timig problems with phase cotrolled ad electroic loads. Clocks ca ru faster ad power electroics, such as SCRs ad switchig diodes, ca misfire ad be damaged. Notchig ca also trip protective relayig, stress power electroics, ad cause excessive heat i motors ad trasformers. 51

4 Fig 3. Three Phase oltages Overlaid. B. UTILITY POWER FACTOR CAPACITOR BANK SWITCHING PROBLEM Eviromet - A medical cliic i Las egas, Nevada, employig sesitive computed tomography (CT Sca) system. Power was brought to the system from a 480 volt service feedig a 480-to-208 volt isolatio trasformer. Problem - CT Sca system was experiecig repeated computer lockups ad compoet failures. Measuremets - The medical equipmet service compay istalled a power moitor o site to aalyze the power to the system. A sigle day of moitorig was eough to idetify the case of the failures. Figure 1shows the disturbace o the lie caused by a utility power factor correctio capacitor bak located just oe block away. Figure 2shows the atteuatio effect of the isolatio trasformer, still ot eough to protect the CT Sca. Fig 4.Disturbace caused by utility capacitor bak Solutio Expasio of the waveform data, Figure 3, revealed the rigig frequecy of the system, whe eergized by the capacitor bak, was betwee 1 khz ad 1.5 khz. This allowed the specificatio of a treatmet device to mitigate the problem. The medical equipmet compay recommeded the use of a active-trackig filter specifically desiged for this type of disturbace aroud 1 khz. The filter was istalled o the 480 -volt lie to protect all of the dowstream equipmet. Figure 4shows the differece betwee the iput (Chael C) ad output (Chael B) of the filter durig a subsequet capacitor bak switchig operatio I.CONCLUSION This work has bee ivolved with ivestigatios associated with the various systems modellig ad its ifluece o the fial reports about equipmet damage aalysis[6],[7]. If this coditio occurs, the groudig represetatio by liear model, although its simplicity, idicates great disadvatages ad strog effects o the fial voltage ad curret results. Moreover, the model that icludes oliear parameters, allowig the iclusio of the previous pheomea, is liked with equatios, iformatio ad complex parameters that are quite difficult to be obtaied[8]. This has motivated the idea of a groud represetatio here proposed. The advatages of this is give by a combiatio of a good respose to disturbaces ad the eed for more simple data. REFERENCES [1] Curtis Roe, Dr. A. P. SakisMeliopoulos, ad Dr. AjaBose,Distributed Dyamic State Estimatio ad Power Quality Moitorig. [2] Z. D. Tsai, D. S. Lee, C.K. Kua, C. R. Che, F. Y. Li, S. H. Chag, ad J. R. Che,.The Effect of Improvig the Temperature ariatio at the SRRC Storage Rig., The 7th Europea Particle ad Accelerator Coferece 52

5 (EPAC), Jue 2000, iea, Austria. I. N. Godim, J. C. de Oliveira, C. E. Tavares, J. A. F. Barbosa Jr. ad M.. B. Medoça [3] Groudig System Modellig ad Its Impact o Computatioal Refudig Aalysis for Equipmet Damages. [4] P. Ferracci, Power Quality, Scheider Electric Cahier Techique o. 199, September [5] D. Chapma, Costs of Poor Power Quality, Power Quality Applicatio Guide Copper Developmet Associatio, March 2001 [6] P. Ribeiro, B. Johso, M. Crow, A. Arsoy, Y. Liu, Eergy Storage Systems for Advaced Power Applicatios, Proceedigs of the IEEE, vol 89, o.12, December [7] D. Chapma, Costs of Poor Power Quality, Power Quality Applicatio Guide Copper Developmet Associatio, March 2001 [8] P. Ribeiro, B. Johso, M. Crow, A. Arsoy, Y. Liu, Eergy Storage Systems for Advaced Power Applicatios, Proceedigs of the IEEE, vol 89, o.12, December [9] Meier, Alexadra vo (2006). Electric Power Systems: A Coceptual Itroductio. Joh Wiley & S [10] Kusko, Alex; Marc Thompso (2007). Power Quality i Electrical Systems. McGraw Hill. [11] Mohamed Awar Abou El-Ata Assessmet of ucertaities i substatio groudigsystem usig iterval mathematics,ai Shams Egieerig Joural (2012) 3,