محاسبه تنش هاي ولتاژي ناشي از كليدزني سريع بر عايق موتورهاي الكتريكي و روش هاي بهبود آن

چكيده انگليسي :

Calculation of the fast switching stresses on electric motors insulation and their improvement methods Mahdi Karimian Kelishadrokhi Mahdi karimian@ec iut ac ir Date of submission 1 6 2019 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiMehdi Moallem moallem@cc iut ac irAbstractIn recent years the use of the power electronic devices and increasing their switching speed by introducing newtechnologies such as silicon carbide switches as well as the use of vacuum switches with high on off rates haveincreased due to technical and economic reasons in the power system This increase in the speed of the power switchescauses two phenomena first it creates traveling waves along the cable between the power supply to the motor whichcauses the voltage to rise at the motor s terminals Secondly high dv dt or high voltage variations cause capacitivecurrents in the motors On the other hand these transients and rapid changes occur in large numbers in seconds tensof kHz which in the long term lead to the aging of motor insulations and ultimately their failure according to studies one of the main causes of electrical motor failure is insulation failure On the other hand in industrial systems longcables are used to connect power supplies to electrical motors These cables today have very low losses which causestransient voltage to be transmitted to the motor terminals with minimum damping Research has shown that the use ofthese cables can lead to an increase in transient voltage at the motor s terminals up to twice the rated value Due to the problems mentioned for electrical motors in the presence of voltage transients this study first presents adetailed and accurate model for studying the transient effects on the electrical motor This model has been expandedusing the theory of multi conductor transmission lines Then in order to increase the simulation speed a summarizedmodel is also obtained using the Krone reduction method In the following using a 360 kilowatt electrical motor andproposed model the effects of voltage transient on the electrical motor has been discussed For simulation theelectrical motor was first studied lonely and the effects of dv dt have been studied on its own After that the cableconnecting voltage source to the motor is also added to the system to verify its effects In these studies the effect oftransient voltage rise time as well as the length of the cable connecting the transient voltage source to the motor onthe overvoltage and the maximum voltage difference between the winding turns has been investigated After identifying the destructive effects of transient voltages on motors the methods for compensating and improvingthem are discussed In the same vein after reviewing the existing methods the RL filter installed on the source sideand the RLC filters installed on the motor side have been investigated The effect of each of these filters on theovervoltage created at the motor terminals and the maximum voltage difference created between the winding turnshas been investigated using simulations Keywords Voltage transients due to switching Multi conductor transmission lines Motor insulation failure Filter

كريميان كليشادرخي، مهدي

محاسبه تنش هاي ولتاژي ناشي از كليدزني سريع بر عايق موتورهاي الكتريكي و روش هاي بهبود آن

شكست عايقي , فيلتر , خطوط انتقال با چند هادي , ولتاژهاي گذرا ناشي از كليدزني