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Performance improvement of synchronous generator by stator winding

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  • 1. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME29PERFORMANCE IMPROVEMENT OF SYNCHRONOUSGENERATOR BY STATOR WINDING DESIGNMr. Sumit Kumar & Prof .Dr. A.A GodboleBharti vidyapeeth Deemed University College of Engineering PuneABSTRACTThe development of an alternate approach for modeling of steady-state performanceof synchronous machines including the effects of harmonics. This approaches shouldpreserve the important property of finite element analysis that each model parameter isrelated to a physical section of the machine its shape, and its material properties.In this reportwinding design is compared with an existing design for the same specification; objectivebehind this winding design is to reduce harmonics, temperature rise and to improve efficiencyof the machine.I. INTRODUCTIONPower systems consist of elements for generation, transmission, distribution andloads. The synchronous machines are the main generating units of power systems. From theload side, synchronous motors are also used. This makes the synchronous machine one of themost important components of electric power systems. The main overall objectives of powersystems are security and reliability. Security of power systems means that the power systemsare within their steady-state power flow constraints. Reliable operation of power systemsrefers to their ability to continuously supply the required electrical energy withoutinterruption under abnormal operating conditions such as faults, switching, and load changes.In both modes of operation the power system behavior is dependent on the electrical andElectro mechanical processes of synchronous machines.Quality of electrical performance is ameasure of how close the electrical output of the generator is to a true sine wave. The actualvoltage waveform from rotating machinery is never perfect. Internal generator and externalload characteristics cause distortions in the wave. These factors impair the consistency of theINTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING& TECHNOLOGY (IJEET)ISSN 0976 – 6545(Print)ISSN 0976 – 6553(Online)Volume 4, Issue 3, May - June (2013), pp. 29-34© IAEME: www.iaeme.com/ijeet.aspJournal Impact Factor (2013): 5.5028 (Calculated by GISI)www.jifactor.comIJEET© I A E M E
  • 2. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME30generator output, and can result in voltage regulator sensing errors and incorrect instrumentreading. In brief; harmonics are energy levels existing at multiples of the fundamental wave’sfrequency. The main source of harmonic is non-sinusoidal field form, which can be madesinusoidal and the total harmonics can be eliminated. But it is not an easy job because air gapoffers maximum reluctance to the flux path due to which air gap cannot be made to varysinusoidally, if air gap is made to vary sinusoidally around the machine, then field formwould be sinusoidal and total harmonics would be eliminated. But field form cannot besinusoidal due to saturation in iron parts and hence we cannot totally eliminate all harmonicsbut can decrease them. Field form is nothing but distribution of flux in machine. This fluxdistribution determines the wave shape of generated voltage in armature winding. In case ofalternators, the voltage and currents induced are having sinusoidal waveforms. But practicallywe cannot get sinusoidal waveforms when such alternators are loaded. Due to the loadingconditions, the generated waveform deviates from ideal waveforms. Such a non-sinusoidalwaveform is called complex wave. By Fourier transform this complex waveform can beshown to be built of a series of sinusoidal waves whose frequencies are integral multiples ofthe frequency of fundamental wave. Sinusoidal components or harmonic functions are calledharmonics of the complex waves. The fundamental wave is defined as that component whichis having same frequency as that of complex wave. The component which is having doubledthe frequency of that of fundamental wave called is called second harmonic. While thecomponent which is having the frequency three times that of fundamental is called thirdharmonic and so on. The complex wave contains both the even as well as odd harmonics. Outof the even and odd harmonics a wave containing fundamental component and evenharmonics only is always unsymmetrical about X-axis whereas a complex wave containingfundamental component and odd harmonics only is always symmetrical about X-axis. In caseof alternators the voltage generated is mostly symmetrical as the field system and coils are allsymmetrical. So the generated voltage or current will not have any even harmonics in most ofthe cases. The waveform distortion can cause problems in voltage regulation, generator andload overheating, and inaccurate instrument readings. Both voltage and current may haveharmonic components. The current components produce heat and are therefore deratingfactors for the generator as well as system motors.II. HARMONIC REDUCTION BY CHORDINGWith the coil span less than the pole pitch the emf generated is proportional to cos(n*α/2).Where,αis angle of chordingn is order of harmonic.The harmonic emf can therefore, be considerably reduced or entirely eliminated by choosinga proper value of α.
  • 3. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME31Figure1 Chording or short pitching of stator windingIII. TECHNICAL DATATable-1 THD at no load for 2/3 winding pitchKva 125Slot 48Winding pitch 2/3Connection Series starPhase 3Volt 415Harmonic no.5 Harmonic no.7THD THDV VCH1 0.886 CH1 0.916CH2 0.841 CH2 0.942CH3 0.822 CH3 0.046Table-2 THD at full load for 2/3 winding pitchHarmonic no.5 Harmonic no.7THD THDV A V ACH1 0.487 2.492 CH1 0.504 2.971CH2 0.469 2.585 CH2 0.637 2.890CH3 0.409 2.575 CH3 0.622 2.805
  • 4. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME32Table-3 THD at no load for 5/6 winding pitchKva 125Slot 48Winding pitch 5/6Connection Series starPhase 3Volt 415Harmonic no.5 Harmonic no.7THD THDV VCH1 0.231 CH1 0.276CH2 0.320 CH2 0.219CH3 0.272 CH3 0.220Figure-2 WDF (4.1%) at no load for 5/6 winding pitchTable-4 THD at full load for 5/6 winding pitchHarmonic no.5 Harmonic no.7THD THDV A V ACH1 0.824 0.351 CH1 0.567 0.590CH2 0.789 0.480 CH2 0.514 0.649CH3 0.791 0.316 CH3 0.637 0.680
  • 5. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME33Figure-3 WDF (4.4%) at full load for 5/6 winding pitchIV. CONCLUSIONThis paper is comparing the result obtained from chording the stator winding by 2/3 and5/6. Harmonic no.5 and harmonic no.7Is reduced by chording the winding by 5/6.we have designed, manufactured and tested a synchronous generator whose harmonic hasbeen reduced.Since harmonic is reduced at design stage cost of power generation isalso not affected.Our work has improved performance of the generator consequently thepower quality.V. ACKNOWLEDGEMENTThe authors wish to thank Mr, A.B, Chaudhuri,Former chief engineer ofCROMPTON GREAVES LTD.AHMEDNAGAR and Mr.N.Sraswati,Project Engineer inCUMMINS GENERATOR TECHNOLOGY LIMITED AHMEDNAGAR for suggestion inconnection with this paper.VI. REFRENCES[1] Paolo mattavelli, member, IEEE “Synchronous frame harmonic control for highperformance ac power supplies”IEEE transactions on industry applications vol.37, no. 3,may/june 2001.[2] Zhu,xi xiao andYongdong li,department of electrical engineering,Tsinghua university,Beijing, 100084, China “ Permanent magnet synchronous motor current ripple reductionwithharmonic back-emf compensation” National high technology research and developmentprogram of China (Project no.2007AA04Z216).[3] T. Yoshida, T. Kamejima, H. Ishikawa and H. Naitoh Gifu University, 1-1 yanagido,Gifu, 501-1193, JAPAN “Higher harmonic currents reduction for interior permanent magnetsynchronous motors” The 2010 International power electronics conference.[4] Katsumi. Yamazaki, and Yu Fukushima Dept. of E. E. C. E., Chiba Institute ofTechnology, 2-17-1, Tsudanuma, Narashino, Chiba, 275-0016, Japan, “Effect of Eddy-Current Loss Reduction by Magnet Segmentation in Synchronous Motors with ConcentratedWindings”.[5] Seok-Hee Han* Wen L. Soong+ Thomas M. Jahns**University of Wisconsin – Madison,WI, USA +University of Adelaide, Adelaide, Australia.“An analytical design approach for
  • 6. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME34reducing stator iron losses in interior PM synchronous machines during flux-weakeningoperation”.[6] Kai Zhang* and Liuchen Chang**Dept. of Electrical and Computer Engineering,University of New Brunswick, CANADA.“Harmonic current reduction for a PWM rectifierwith very low carrier ratio in a microturbine system”. 0-7803-8886-0/05/$20.00 ©2005 IEEECCECE/CCGEI, Saskatoon, May 2005.[7] T. Onuki, T. Iwamoto, W.1. leon, H.Watanabe, S. Katoh, and A. Nakamoto Electrical,Electronics and Computer Engineering,Waseda University34-1 Ohkubo Shinjuku-ku,Tokyo169-8555, JAPAN“ A novel rotor construction for reducing higher space harmonics in thepermanent magnets synchronous motor”.078034879.6/98/$10.00 Q 1998 IEEE.[8] Pradipta K. Das and Amulya K. Das Gupta, Member, IEEE.“Inductance Coefficients ofThree-Phase Inductor Alternators: Part I Analytical Study.”IEEE TRANSACTIONS ONPOWER APPARATUS AND SYSTEMS, VOL. PAS-88, NO. 11, NOVEMBER 1969.[9]A.K.Sawhney,Design of electrical machine Dhanpat Rai and Publishing Company Ltd.[10] Technical manual UC27-V CUMMINS GENERATOR TECHNOLOGY.[11] Pooja Agrawal and Ritesh Diwan, “Sensorless Control of Surface-Mount Permanent-Magnet Synchronous Motors”, International Journal of Electrical Engineering & Technology(IJEET), Volume 4, Issue 2, 2013, pp. 112 - 119, ISSN Print : 0976-6545, ISSN Online:0976-6553.[12] Vishal Rathore and Dr. Manisha Dubey, “Speed Control of Asynchronous Motor usingSpace Vector Pwm Technique”, International Journal of Electrical Engineering &Technology (IJEET), Volume 3, Issue 3, 2012, pp. 222 - 233, ISSN Print : 0976-6545,ISSN Online: 0976-6553.