Modelling of oil impregnated paper transformer bushing on electric field and hot spot temperature using finite element method

A transformer bushing is the weakest part in a power transformer. Often, damage to this part will result in the failure of the electrical system as a whole. Pollution from industrial areas is one of the possible causes of the increase in the value of electric field distribution. In addition, high load demand can cause a temperature rise on the transformer bushing. This study focused on a transformer bushing with a nominal rate of 145 kV. The transformer in 2D form was first developed before analysis on electric, voltage, and temperature distributions carried out using finite element method software. Temperature distribution analysis is needed to identify the hottest point (HST) on the transformer bushing during operation. The transformer bushing design is implemented using a computer-aided design (CAD) software. The parameters for the 2D design are obtained from the journal and from the transformer bushing manufacturer. There are three levels of pollution considered in this study, namely low, medium, and high. Subsequently, the analysis of the effects of several levels of pollution and the increase in load on the transformer bushing was performed using finite element method software. Upon completion of the design using CAD software, the transformer bushing in clean condition is first analyzed to ensure its integrity and used as a baseline result. Further, from the analysis, it was found that the presence of pollution on the surface of the transformer bushing, the electric distribution increased in line with the increase in pollution level. The designed transformer bushing has been validated with several reseacher in term of its voltage distribution and electric field at several parts and it is found satisfactory. The electric field value has increased with the level of pollution. Based from analysis, with high level of pollution, the value of electric field at first shed has increase up to 90 % and the value has increased 22 % between shed number 16 to 18. In this thesis, a mathematical equation for voltage distribution has been propsosed. For analysis of temperature distribution, when the load increases beyond the rated current which is 2500 A, the HST point in the transformer bushing moves from the oil side to the air side area, which is on the porcelain side. The HST value also increased. This proves that regular maintenance work to clean the surface of the transformer bushing should always be carried out. Increased load demand also needs to be controlled so that it does not exceed the rated value of the transformer bushing. The movement of HST point from the oil to the air sides due to gradually increasing of load demand is presented. Then, the relationship between the HST point and the injected current to the transformer bushing is represented in the form of mathematical equation.