Analiza naprave za merjenje upornosti navitij elektromotorjev

OPREŠNIK, MATEJ (author), Bojkovski, Jovan (mentor)

Upornost navitja je ena izmed najpomembnejših lastnosti elektromotorjev, ki jo potrebujemo za presojo, ali je motor ustrezen. Upornost merimo s štiri-točkovno metodo merjenja upornosti. Diplomska naloga se osredotoča na probleme, s katerimi se srečujemo v laboratoriju podjetja pri meritvah upornosti navitja. Naloge smo se lotili pri predstavitvi najpogostejših meritev v laboratoriju in kalibraciji laboratorijske naprave ter mikroohmmetra z uporabo referenčnih uporov. S tem smo preverili ustreznost naprav za izvajanje nadaljnjih poizkusov in raziskav. Nato smo se osredotočili na vpliv segrevanja navitja zaradi merilnega toka. Če želimo izmeriti upornost navitja, moramo skozenj spuščati nek tok. Vendar če je ta tok prevelik, lahko pride do nezaželenega gretja navitja, ki povzroča napačno izmerjene vrednosti. Ugotovili smo, da je ta problem bolj izrazit pri večjih upornostih, saj se takrat troši več moči na navitju. Določili smo, da se upornosti nad 100 mΩ meri z merilnim tokom 1 A. S termočleni smo tudi preverili, koliko se stator motorja segreje pri različnih merilnih tokovih. Preverili smo tudi, kako ničelna napetost vpliva na meritve na dveh laboratorijskih napravah in primerjali napravo z merilnim območjem 10 V in 300 V. Opazili smo, da ima naprava z višjim merilnim območjem precej večjo ničelno napetost in zato brez ustreznih rešitev ni primerna za manjše upornosti, saj ničelna napetost, izmerjena ob kalibraciji naprave, morda ni več ista. Implementirali smo tudi kompenzacijo ničelne napetosti pred vsako meritvijo upornosti. Z odstranitvijo rotorja smo hoteli ugotoviti, če se s spremembo induktivnosti spremeni tudi upornost. Ob zmanjšanju induktivnosti za petino, bistvene razlike v upornosti nismo opazili. Zaključili smo, da induktivnost nima bistvenega vpliva na upornost, pri vrednostih, s katerimi se srečujemo v laboratoriju. Nazadnje smo še s simulatorjem vezij preverili, kako kontaktne upornosti in upornosti žic vplivajo na izmerjeno upornost pri motorjih z dvema navitjema. Opazili smo, da kontaktne upornosti in upornosti žic z vrednostjo manj kot nekaj mΩ, nimajo pomembnega vpliva na rezultat. Ugotovili pa smo, da če sta dve izmed upornosti več kot 5mΩ, pridemo lahko hitro do napake 2%, ki jo morda ne opazimo brez natančnejše analize.

• Language: Slovenian
• Keywords: upornost, štiri-točkovna metoda, ničelna napetost, merilni tok, odstopanje
• Work type: Bachelor thesis/paper
• Organization: FE - Faculty of Electrical Engineering
• Year: 2023
• PID: 20.500.12556/RUL-153307
• COBISS.SI-ID: 178523139
• Publication date in RUL: 21.12.2023

Secondary language

• Language: English
• Title: Analysis of a device for the measurement of the resistance of the electric motor windings

Abstract

Winding resistance is one of the most important characteristics of electric motors, which we need to judge whether the motor is adequate. Resistance is measured using the four-point resistance measurement method. The diploma thesis focuses on the resistance measurement problems encountered at the company laboratory. We tackled the tasks by presenting the most common measurements done in the laboratory and calibrating the laboratory device and the microohm-meter using reference resistors. With this, we checked the suitability of the devices for carrying out further tests and research. Then we focused on the influence of winding heating due to the measuring current. If we want to measure the resistance of the winding, we have to pass some current through it. However, if this current is too high, unwanted heating of the winding may occur, causing incorrect measured values. We have found that this problem is more pronounced with higher resistances, since more power is wasted on the winding. We determined that resistances above 100 mΩ should be measured with a measuring current of 1 A. We also checked with thermocouples how much the motor stator heats up at different measuring currents. We also checked how the offset voltage affects the measurements on two laboratory devices and compared the device with a measuring range of 10 V and 300 V. We noticed that a device with a higher measuring range has a much higher offset voltage and therefore, without suitable solutions, it is not adequate for lower resistances, since the offset voltage measured during device calibration may no longer be the same. We also implemented offset voltage compensation before each resistance measurement. By removing the rotor, we wanted to find out if the change in inductance also changes the resistance. When reducing the inductance by a fifth, no significant difference in resistance was observed. We concluded that inductance has no significant effect on resistance with the values encountered in the laboratory. Finally, we used the circuit simulator to check how contact resistances and wire resistances affect the measured resistance of motors with two windings. We noticed that contact resistances and wire resistances with a value of less than a few mΩ do not significantly affect the result. However, we have found that if two of the resistances are more than 5mΩ, we can quickly reach an error of 2%, which may not be noticed without a closer analysis.

• Keywords: resistance, four-point method, offset voltage, measurement current, deviation