International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 03 | Mar -2017
p-ISSN: 2395-0072
www.irjet.net
Protection Schemes for Three Phase Induction Motor Jayesh Narhare1,Harshal Patil2, Sangita Patil3, Mrutyunjay Patted4 1,2,3 UG Student,Dept Of Electrical Engineering, Jspm’s
Bsiotr Wagholi, Pune,Maharashtra,India
4 Assistant Professor, Dept Of Electrical Engineering, Jspm’s Bsiotr Wagholi, Pune,Maharashtra,India
---------------------------------------------------------------------***--------------------------------------------------------------------Abstract-This paper contributes for the analysis and the suggested protection against individual phasing of threephase induction motors. Practice is showing that significant number of three-phase motors is damaged due to individual phasing. At such conditions the current increases considerably and the engine is subjected to burnout. Accordingly, this may cause long production interruptions in the relevant industries. Generally all motors are protected against thermal overloading by bimetal relays, but they are not always capable to ensure protection at individual phasing. As a result of the current research, a reliable electronic protection is proposed that can trip-off any threephase engine in a case of individual phasing. Such protection is especially priceless when applied to high energy motors. The suggested protection is designed to react instantly whenever anyone of the engine line currents becomes zero. a signal from the protecting circuit switches-off the engine starter in case of failures of anyone of the three phases. KeyWords: overloading , single phasing ,under and over temperature. 1. INTRODUCTION Long-term three-phase engine operation depends upon the proper selection of its protection. When one of the stator winding remains without voltage supply the engine continues to operate as a solo-phase gagdet, drawing energy from the remaining two phases. This method of operation is named solo phasing and could occur for instance when one of the fuses the three-phase engine lines "blows" and disconnects one of the stator windings. Surveys in many industries show that the main reasons for three-phase engine failures are the thermal overloading as a result of voltage or load variations, rotor blockages or solo phasing. Thermal overloading and solo phasing cause up to 44% of malfunction cases . Due to the phenomenon of the solo phasing, the current of the engine increases considerably. If the protection does not operate instantly, the engine overheats and its operation fails, causing downfalls in the particular industry. In the majority of the applications bimetal over load relays (ORL) are used for the engine protection. These relays are not always effective to preserve the three-phase engine against solo phasing. The objectives of this research are to describe the reaction of the bimetal OLR in cases of solo Š 2017, IRJET
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Impact Factor value: 5.181
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phasing and to propose an automatic electronic solo phasing protection. 1.1 over temperature Since the current drawn by the engine is more, heat dissipation in the stator and rotor is increased drastically when the percentage balanced over voltage exceeds 25%. Hence it is recommended to operate the engine within 10% of balance over voltage. 1.2 single phasing phasing could occur at startup or at running conditions, when the engine is fully loaded, under-loaded or overloaded. The stator windings could be star or delta connected. The reaction of the bimetal over load relay (OLR) is described below assuming that it is set at the rated line engine current. At individual phasing an engine cannot develop starting torque, since an individual-phase individual current produces a pulsating magnetic field with two elements rotating in opposite directions - forward and reversed. Both elements produce equal torques acting in opposite directions and due to this fact the engine cannot begin. This phenomenon can be examined for the two viable engine connections. 2. Overloading The three-phase engine is overloaded with little currents in the range of I = (1.05 to1.2) IR, where IR is the rated current of the engine. This is due to little load or voltage variations. Under these conditions the engine could operate for a long moment period and should be tripped-out at a moment of about 2 hours, whereby the aging of the insulation will not be affected. The action of the OLR in this case is not very exact, because of the nature of the moment-current characteristic and the significant location of momentresponse dissipation. At the same overloading currents one and the same OLR could give very dissimilar momentresponses. Case 2: The three-phase engine is overloaded with currents in the range of I = (1.2 to 1.5) IR due to light overloading. The tripping moment for a current of 1.5IR should be less than 2 minutes to evade overheating and burnouts. ISO 9001:2008 Certified Journal
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