OPTIMIZATION OF INSTRUMENT TRANSFORMER'S HOUSING USING FINITE ELEMENT METHOD

Tema ovog diplomskog rada je konstrukcijsko-ekonomska analiza postojećeg dizajna kućišta mjernog transformatora uz poseban osvrt na ponašanje kućišta pri seizmičkim opterećenjima te razvoj novog, optimiranog kućišta na temelju dobivenih podataka. Mjerni transformator je statični uređaj koji je, zbog svoje specifične (vitke) konstrukcije, u slučaju potresa izložen velikim dinamičkim opterećenjima koja uzrokuju znatna naprezanja u kućištu i izolatoru transformatora. Bitna odrednica ovog rada jest konstrukcija kućišta. Dosad nije provedena optimizacija kućišta iz više razloga. Možda najbitniji je taj da nije bilo alata kojim bi se provjerila ovisnost naprezanja o konstrukciji kućišta (primarno debljini lima). Dolaskom modernih inženjerskih alata poput ANSYS-a na tržište, inženjerima je dostupan moćan alat kojim mogu raditi ispitivanja, a da ne potroše velika sredstva i vrijeme na eksperimentalna testiranja različitih konstrukcija. Želja je dobiti jasnu sliku može li se uopće optimirati postojeće kućište (postoji mogućnost da nema prostora za optimiranje) i na temelju toga dati smjernice za daljnje postupke pri pronalasku rješenja koja će doprinijeti boljem i, u konačnici, sigurnijem ponašanju transformatora pri seizmičkim opterećenjima. Ovisno o geografskom području, postoje različito seizmički klasificirana područja. Iz te perspektive, želja je ovog rada ukazati na smjer za daljnju optimizaciju cjelokupnog proizvodnog raspona kućišta s krajnjim ciljem dobivanja proizvodne game kućišta primjerenih potresnom području u kojem se transformator nalazi. Provedeno je kompletno pojednostavljenje modela transformatora te u softverskom alatu ANSYS napravljena statička i modalna analiza modela. Na temelju tih rezultata provedena je spektralna analiza prema zahtjevima standarda IEEE 693-2018. Rezultati su zadovoljili sve uvjete ranije spomenutog standarda. Zaključeno je da prostor za optimiranje kućišta postoji te je napravljena optimizacija debljine limova unutar softverskog alata metodom odzivne površine čime je kreiran set pokusa s različitim kombinacijama debljine limova te dobivena četiri najbolja kandidata. Od ta četiri kandidata odabran je onaj s najmanjom masom te provedena dodatna statička, modalna i spektralna analiza tog rješenja kako bi se potvrdio odabir. Rezultati su zadovoljili postavljene uvjete te je odabrana kombinacija limova koja značajno smanjuje masu uz zadržavanje naprezanja u kućištu i izolatoru transformatora u dozvoljenim granicama. Predložen je daljnji rad na optimizaciji kućišta te dan smjer za kreiranje familije proizvoda kojom bi se kućišta podijelila u standardne grupe iz kojih bi se prilikom projektiranja proizvoda odabirala ona koja zadovoljavaju seizmičke uvjete određenog tržišta.Main topic of this thesis is constructional and economic analysis of the existing housing for instrument transformers, with special emphasis on housing behavior during seismic loads. The thesis also suggests development of a new, optimized housing based on obtained data. Instrument transformer is a static device which, due to its specific (slim) design, is subjected to high dynamic loads during earthquakes. These loads cause significant stresses in transformer's housing and insulator. Goal of this thesis is to get a clear picture of whether or not the existing housing can be optimized (there is a possibility that there is no room for optimization) and on that basis provide guidelines for further procedures in finding better solutions that will contribute to a better and ultimately more robust transformer behavior at seismic loads. So far no optimization of housing has been done for several reasons. One of the main reasons is that there were no tools to check the stress dependence on housing design, primarily the thickness of the sheet. With the arrival of modern engineering tools such as ANSYS, engineers have a powerful tool that can do simulations without spending significant resources and time on experimental testing of different designs. Depending on the geographic area, there are different seismically classified areas. From this perspective, goal of this paper is to provide guidelines for further optimization of the entire production range of housings with the ultimate aim of obtaining a manufacturing range of housings suitable for the earthquake area in which transformer is located. The transformer model was simplified and ANSYS software tool was used for static and modal analysis. Based on these results, spectral analysis was performed according to IEEE 693-2018 standard requirements. The results fulfill all requirements of IEEE 693-2018 standard. Conclusion is that there is room for housing optimization. Following from that, optimization of sheet thickness was carried out with the software tool using the response surface method. A set of experiments with different combinations of sheet thickness were created and the four best sheet thickness combinations were chosen. The combination with the smallest mass was selected and additional static, modal and spectral analysis of this solution was performed to confirm the selection. The results satisfied required conditions and selected combination of sheets significantly reduces the housing's mass while keeping the stresses on the housing and on the transformer insulator within the permitted limits. Further housing optimization work is proposed. The direction for the creation of a product family with housings divided into standard groups is also proposed. During product design, the housing that meets the seismic requirements of a particular market would be chosen