New improvement way of induction motors for a variable speed drive when changing mass dimension indices has been proposed. It allows for improvement of energy indices and reduction of running costs. The analysis of simulation results has been carried out and calculation results of economic efficiency of the achieved methods of approach to energy effective induction motors design have been suggested

Muravleva, О.О.

Tyuteva, Polina Vasilievna

Electronic archive of Tomsk Polytechnic University

IntroductionEnergysaving, or rather production rationalization,distribution and use of all kinds of energy, became oneof the main priority trends of technological policy in alldeveloped countries of the world. The potential of energysaving in Russia is 40...45 % of present energy consumption in the country according to specialists’ estimation, that makes 360...430 mln. tons of equivalent fuel. Branches of fuelenergy complex have a third part ofthis economy potential, another third is concentrated inpowerintensive branches and building industry, morethan 25 % is in housing and communal services, 7 % isin transport and 3 % is in agriculture [1]. European potential in energysaving is evaluated at 160 mln.tons ofequivalent fuel that is considerably lower than the sameindex in Russia. Energy intensity of domestic goods is,as a rule, 2,5...3 times higher than in Europe and USA.It gives the reasons to consider Russian potential of energysaving as a vast resource of economical and socialdevelopment, concentrated in all fields of practical activity and so far unused properly.The structure of electric energy consumers in Russiais approximately as follows: electric drive – 60 %, electric transport – 9 %, electrothermics and electrotechnics – 10 %, lightning and other consumers – 21 %.According to the data of European experts, the cost ofelectric energy, consumed annually by an average motorin industry, is 5 times higher than its own cost. It is obvious that during the motor operating time (tens of years) an energy component is incommensurably higherthan the component of capital costs. In this connection,the care of optimization just the energy component is ofprime importance.Modern level of development of power electronics,microintegrated control systems, theory and means of automatic control allow using widely these theoretical andtechnical achievement for solving tasks of energy andresource saving. Modern frequency converters provide thequality of control of induction motors (IM) rate being justas good as the quality of direct current drive. The wellknown advantages of induction squirrelcage motor suchas high reliability, lower cost, simplicity in production andusage, in conjunction with high regulating and dynamicindices supported at present turn the induction variablefrequency drive into the dominant type of variable speeddrive. Its mass application allows solving not only processtasks, but also energysaving problems.Industry gets out of recession and large quantity ofelectric energy is required now. It may be provided intwo ways:• by introduction of new generating capacity;• by meeting industry requirements due to energysaving.The first way is connected with high capital investments and long period of these capacities introduction,that slows down industry development. The second waymay be provided by means of introduction of a variablespeed drive with energysaving induction motors. In thiscase, while the problem of energysaving at variablespeed drive introduction is sufficiently considered, theproblem of manufacturing of special energysaving IM,operating in electric drive structure, is not practicallyconsidered. And it is in IM where the main electric energy losses arising at electric drive operating occur. Therefore, the development of new approaches to IM improvement intended for variable speed drive is required.The aim of the given paper is the improvement of induction motors for variable speed drive subject to theireconomical efficiency.Statement of the investigation problem The induction motor, as an electromechanic energyconverter, is the main device, being a part of electric drive. The objects of our attention are IM with squirrelcage rotor. The current economic changes have definedthe necessity of IM improvement and determined newtrends of their development. The main trend of standardIM improvement is the increase of power efficiency [1].IM power efficiency is characterized by the efficiency level (η) and power factor (cosϕ). In European Community and Russian Federation the standards for IM efficiency were accepted in 2000. СЕМЕР euro standardsfor two and fourpole IM with the capacity from 1, 1 to90 kWt three levels of efficiency are provided: normal –EFF3; advanced – EFF2 and high – EFF1 (EFF – efficiency class) [1]. EFF2 and EFF1 standards are partially presented in [1]. Efficiency values lower than EFF2level are referred to EFF3 level. Standards of SS Р516772000 involve motors of all poles in the range ofcapacity from 1, 1 to 400 kWt. They provide two levels ofefficiency, which practically coincide with the levels ofeuro standards of СЕМЕР (European Committee ofManufacturers of Electrical Machines and Power Electronics): normal EFF2 and advanced EFF1.Engineering163UDC 621.313.333:658.562INDUCTION MOTORS IMPROVEMENT FOR A VARIABLE SPEED DRIVEО.О. Muravleva, P.V. TyutevaTomsk Polytechnic UniversityEmail: MuravlevaOO@tpu.ru, TyutevaPV@sibmail.comNew improvement way of induction motors for a variable speed drive when changing mass dimension indices has been proposed. It allowsfor improvement of energy indices and reduction of running costs. The analysis of simulation results has been carried out and calculationresults of economic efficiency of the achieved methods of approach to energy effective induction motors design have been suggested.Recently the new trend in creation of energysavingIM has appeared. It is a design of IM with higher in comparison with base machines of massdimensional indiceswhich is realized in the given paper. To create energysaving IM for working in the system of a variable speed drive the following ways of their design are possible [2]:• without changing transverse geometry at changinglength of starter and rotor cores;• without changing transverse geometry at changinglength of starter and rotor cores, and also changingmachine winding data;• at changing transverse geometry of starter and rotor.The first two ways of energysaving IM design wereconsidered in the paper. A mathematical model of economic efficiency estimation at IM design was used forsimulation. It covers the main stages of IM design, suchas electromagnetic [3] and thermal calculation of amachine [4], and also includes economic calculation allowing us to estimate the optimality of the designedmachine at the design stage. The mathematical modelof economic efficiency estimation may be used for simulation of any average capacity IM of general industrial performance. Any stage of simulation may be performed separately, and adjustment is also possible at anystage. The advantage of mathematical models is, first ofall, the fact that they exclude any physical experiment.The transverse geometry of base machines is accepted as initial parameters: inner and outer diameter ofstarter and slot zones, characteristics of applied active,insulator and structural materials. The limiting factors ofsimulation are the coefficient of slot fillingup and starter winding heating. To calculate the thermal pattern ofthe machine the method of flow diagram, based on wideuse of thermal resistances which are connected intothermal net, imitating real ways of transmission of thermal flows in the machine was used. The method of thermal diagrams became the most widely used due to itssimplicity and sufficient accuracy of simulation [4]. InIM of average power the insulation with heat resistanceF class possessing 100 °С maximum temperature excessof electric machine parts, at gaseous medium temperature of +40 °С and orthometric height not more than1000 m is used. Since IM starter is the most heated partof the electric machine at steadystate conditions, thevalue of an average temperature excess of starter winding(Θм) is accepted as the output parameter of thermal calculation. The value of average temperature excess ofstarter winding allows judging roughly about the reliability of the designed electric machine. It is generallyknown that the excess of insulator operating temperature by 5...10 °С decreases its service life in two times.The following energy characteristics are accepted asthe output parameters of the mathematical model of economic efficiency evaluation: efficiency and power factor,and also economic indices, such as referred costs Зт ofdevelopment, introduction, manufacturing and operation of the motor for standard recoupment period andannual costs for active electric energy losses Сa for technical and economic assessment of optimal variant selectionwhere Сд is the total cost of the motor; Са is the annualcosts of active electric energy losses; tn is the standard recoupment period,where Сm is the costs for materials; Сl is the labor costs;Сne is the nonproductive expenses,where Ца is the cost of 1 kW·h of electric energy; t is thenumber of working hours of the motor per year; К is theload factor; Р2 is the useful power at motor shaft; η is themotor efficiency at actual load.The lowest referred costs Зт for development, introduction, manufacturing and operation of the motor during the standard recoupmentk period serve as the criterion of economic efficiency at the choice of the best variant [5, 6]. Besides, motor prior cost, which includesmotor total cost and also the rate of profit ρн of enterprisemanufacturer, is taken into considerationAlgorithm of simulation of IM economic efficiencyis shown in Fig. 1.Fig. 1. Algorithm of calculation of IM economic efficiencyThe task of simulating is to determine economic efficiency at machine running, being guided by its specified geometry, and to make a decision on the appropriateness of the realized direction in IM improvement.Initial parameters input Electromagnet calculation of IM Thermal calculation of IM Economic calculation of IM Graphic dependences plotting Conclusions (1 ).äâèã ä íÖ Ñ ρ= +21 ,à àÑ Ö tKPηη−⎛ ⎞= ⎜ ⎟⎝ ⎠,ä ì ò âíÑ Ñ Ñ Ñ= + +1( ) ,ítò ä à iiÇ Ñ Ñ== +∑Bulletin of the Томsк Pоlytеchnic University. 2007. V. 310. № 2164The analysis of simulated results IM AIR112М2, AIR112М4 with squirrelcage rotorwere taken for simulating. AIR112М4 was selected as themost widespread IM with stable parameters at manufacturing, and AIR112М2 is used more often in housingand communal services. The following ways of energysaving IM design, used in this paper, may be singled out:• the increase in length of starter and rotor cores (l)without changing the number of turns of starter windings (w1);• the increase in length of starter and rotor cores anddecrease of starter winding number of turns.The change of length of starter and rotor cores of themachine was taken in the range from 100 to 130 % of gauge length, and the change of starter winding number ofturns in the range from 100 to 85 % from the base value.The dependences of the complex efficiency index,representing the product of power factor and efficiencyof the designed motors at changing winding data and thelength of starter and rotor cores are shown in Fig. 2. Asit is seen from the Figures, at IM weight increase the improvement of energy indices occurs due to electric losses reduction, falling at starter and rotor winding. In thiscase, the complex efficiency index turns out to be higher than the index of the base motor for the variants withsimultaneous change of the number of turns in the starter phase winding and the length of starter and rotor cores. The best complex efficiency index results fromnumber of turns decrease in starter phase winding by10 % from the base value.The dependences of annual costs for active losses ofelectric energy depending on the length of starter androtor cores at the change of number of turns in the starter phase winding are presented in Fig. 3. The decreaseof annual costs for active losses of electric energy whichare the main item of expenses at IM service occurs dueto the energy indices improvement. The least value ofelectric energy active losses occurs at the decrease of thenumber of turns in the starter phase winding by 15 %from the base value.The dependences of the referred costs for the development, introduction, manufacturing and operation ofIM for the standard recoupment period at the change ofwinding data and the length of starter and rotor coresare shown in Fig. 4. The referred costs for the development, introduction, manufacturing and operation of amotor for the standard recoupment period and the annual costs for the active losses of electric energy are minimal at the decrease of the number of turns of starterphase winding by 15 %. The decrease of the referredcosts for the development, introduction, manufacturingand operation of IM for the standard payback periodoccurs due to the decrease of annual costs for activeelectric energy losses. In this case, minimal values of thereferred costs fall at the variants of simulation at the simultaneous change of core length and the number ofturns in the starter phase winding.Engineering165Fig. 2. Complex efficiency index η·cosϕ depending on the length of starter and rotor cores at change of the number of turns in starter phase winding for: a) AIR112М2; b) AIR112М4Fig. 3. Annual costs for electric energy active losses depending on the length of starter and rotor cores at the change of the numberof turns in the starter phase winding for: a) AIR112М2; b) AIR112М4? ? ? ?74767880828486100 105 110 115 120 125 130100 % w1 90 % w1 85 % w1l , %? a , USD ?)60626466687072100 105 110 115 120 125 130100 % w1 90 % w1 85 % w1l , %? a , USD ?)0,7200,7400,7600,7800,8000,820100 105 110 115 120 125 130100 % w1 90 % w1 85 % w1l ,%?•cos? ?)0,6900,7050,7200,7350,7500,765100 105 110 115 120 125 130100 % w1 90 % w1 85 % w1l , %?•cos? ?)The dependences of squirrelcage IM cost at thechange of winding data and the length of starter and rotor cores are presented in Fig. 5. As it was expected IMturns out to be rather expensive than its analogue due tothe increase of costs for the materials, which are themain expenses, included into the prime cost and alsodue to the growth of labor costs. The growth of IM costoccurs linearly; it is connected with the fact that thecosts for materials grow proportionally to the increase ofcore length. But a certain growth of IM cost due to theincrease of active materials consumption is compensated due to decrease of annual costs for electric energyactive losses.ConclusionThe realization of the suggested trend of IM improvement for the variable speed drive, connected with theincrease of massdimensional indices of IM, allows designing the machine, possessing the advanced energycharacteristics and lower costs, during the operation life. In this case, the best energy indices are obtained atthe simultaneous change of cores length and the number of turns in starter phase winding. The designed IMpossesses the energy indices which correspond to theincreased efficiency level according to the СЕМЕРEFF2 euro standards and to the normal efficiency levelaccording to the SS Р 516772000.Energy indices turn out to be higher for the variant ofsimulation at the reduction of the number of turns of starter cores by 10 % at relative value of core length of 125 %.The referred costs for the development, introduction,manufacturing and operation of the motor for a standardrecoupment period and annual costs for the active electric energy losses are lower for the variant at the decreaseof the number of turns in starter phase winding by 15 %and relative value of core length of 115 %. It confirms once again the fact that optimal induction motor should bechosen for the specific operation conditions.Improved energy indices allow reducing the costsduring the operation life that compensates the increaseof induction motor cost. Minimal value of the referredcosts for the development, introduction, manufacturingand operation of the induction motor for the standardrecoupment period is at the decrease of the number ofturns in starter phase winding by 15 % and relative valueof core length of 115 %. Thus, the designed motors areeconomically the most profitable.The induction motor cost for any variant of calculation is higher than the cost of the analogue, due to theincrease of active materials consumption as well as thegrowth of labor costs. But a certain increase of the costof the designed induction motor is compensated by thereduction of costs during the operation life for the variants of simulation with the decreased number of turns inBulletin of the Томsк Pоlytеchnic University. 2007. V. 310. № 2166Fig. 4. The referred costs for the development, introduction, manufacturing and operation of induction motor for the standard recoupmentk period depending on the length of starter and rotor cores at the change of the number of turns in the starter phasewinding for: a) AIR112М2; b) AIR112М4Fig. 5. The cost of a squirrelcage IM depending on the length of starter and rotor cores at the change of the number of turns in starter phase winding for: a) AIR112М2; b) AIR112М495100105110115120125100 105 110 115 120 125 130100 % w1 90 % w1 85 % w1l , %????? , USD ?)9095100105110115120100 105 110 115 120 125 130100 % w1 90 % w1 85 % w1l , %????? , USD ?)690703716729742755768100 105 110 115 120 125 130100 % w1 90 % w1 85 % w1l , %?? , USD ?)590604618632646660674100 105 110 115 120 125 130100 % w1 90 % w1 85 % w1l , %?? , USD ?)starter phase winding. The analysis of simulation resultsshows that the increase of core length over 115...120 %from the base length is not reasonable.The realization of the trend of IM improvement,connected with the design of energysaving IM at thechange of starter and rotor transverse geometry, is furtherexpected. It allows turning to the high efficiency level according to СЕМЕР EFF1 euro standards and higher efficiency level according to SS Р 516772000. However, itdemands carrying out additional scientific research.Engineering167REFERENCES1. Lipatov Yu.A. Power supply: reality and perspectives // Appendix tothe Journal «TEC i Resursy Kuzbassa». – 2005. – № 2. – P. 22–25.2. Muravlev O.P., Muravleva O.O., Tyuteva P.V. Induction motors as abase of energysaving technology in a variable speed drive // ActualProblems of Alternative and EnergySaving Technologies: Proceeding of AllRussian Scientific and Technical Conference at International Participation. – Yekaterinburg: USTU Press – UPI, 2006. –P. 286–291.3. Design of electric machines / I.P. Kopylov, B.K. Klokov, V.P. Morozkin, B.F. Tokarev; Edited by I.P. Kopylov. – Moscow: VysshayaShkola, 2002. – 757 p.4. Sipaylov G.A., Sannikov D.I., Zhadan V.A. Thermal, hydraulic andaerodynamic design in electric machines. – Moscow: VysshayaShkola, 1989. – 239 p.5. Generalpurpose induction motors / Edited by V.M. Petrov andA.E. Kravchik. – Moscow: Energiya, 1980. – 488 p.6. Muravleva O.O., Usacheva T.V. Economical efficiency estimation atinduction motors production // Bulletin of the Tomsk PolytechnicUniversity. – 2006. – V. 309. – № 1. – P. 186–189.Received on 22.09.2006

Induction motors improvement for a variable speed drive

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