en Diagnostics Techniques Diagnostics Techniques Research Paper Research Paper <span style="font-size:10.0pt"><span new="" roman="" style="font-family:" times="">Bushings are one of the most important components of electrical equipment such as power transformers, reactors, capacitors. Most of the installed bushings have Oil-Immersed Paper (OIP) insulation structure. Bushing failure is caused by various reasons such as poor manufacturing process, overloading and also poor installation process, but moisture ingress is one of the main reasons of OIP bushing defect during its operation. In this paper, the electric field distribution of OIP bushings in multiple situations are simulated and effects of moisture distribution are analyzed. The simulations are stablished in polluted and clean surfaces of the studied bushing and done by COMSOL Multiphysics Software. The results show that non-uniform moisture distribution has a significant effect on electric fields of OIP insulation. This effect strongly increases with increasing the pollution on the external insulator of the bushing.</span></span> Finite Element Method (FEM), Moisture, OIP Bushing, Pollution, Transformer 48 59 http://ijeee.iust.ac.ir/browse.php?a_code=A-10-789-13&slc_lang=en&sid=1 Mohammad Abouhosseini Darzi md.abouhosseini@stu.nit.ac.ir 1800319475328460017250 1800319475328460017250 No Department of Electrical & Computer Engineering, Babol Noshirvani University of Technology, Babol, Iran. Mohammad Mirzaie mirzaie@nit.ac.ir 1800319475328460017251 1800319475328460017251 Yes Department of Electrical & Computer Engineering, Babol Noshirvani University of Technology, Babol, Iran. Amir Abbas Shayegani Akmal shayegani@ut.ac.ir 1800319475328460017252 1800319475328460017252 No Department of Electrical Engineering, University of Tehran, Tehran, Iran. Ebrahim Rahimpour ebrahim.rahimpour@thws.de 1800319475328460017253 1800319475328460017253 No Institute of Electrical Power Engineering and High Voltage Technology, THWS, Schweinfurt, Germany.