Search

Highlight • Under DC voltage, surface charge indicates polarity effect. • Increasing the voltage amplitudes led to an increase of the surface charge density. • Corona voltage and the charging time for both polarities rise, the amount of charges increases linearly. • Relationship between amount of surface charges and number of photons have been carried out using corona camera. Abstract The objective of the present study is to investigate the surface charge measurement on the surface of polymeric insulator under AC and DC voltages experimentally. According to the test results, increasing the voltage amplitudes led to an increase of the surface charge density, the voltage application duration was also extended. During the tests, it was observed that as the corona voltage and the charging time for both polarities rise, the amount of charges increases linearly. The results show that more surface charge was deposited by negative corona charging when compared with positive corona charging. Also in this paper, the effect of the corona variations on the amount of surface charge have been investigated. For this purpose, relationship between amount of surface charges and number of photons have been carried out using corona camera. Moreover, attempt was made to investigate the effects of surface charges on potential and electric field distribution along polymeric insulator under AC and DC voltages using computer simulations based on finite element method (FEM). The present paper was conducted to study the effects of magnitude, polarity, and location of surface charges on surface potential distribution along the insulator. [ABSTRACT FROM AUTHOR]

Abstract: This paper extracts a comprehensive reliability model for a transformer with oil natural air forced (ONAF) cooling system, which is the most common type of power transformers. The transformer is first classified into three subsystems and a reliability model is thereafter developed corresponding to each subsystem. Markov process and frequency/duration approaches are applied to analyze the extracted models and achieve their equalized representations. Merging subsystem models leads to the transformer entire reliability model consisting 17 states. The model is then reduced to an 11-state one which is more computationally manageable. Numerical analyses and sensitivity studies are conducted to demonstrate the performance of the proposed model and the results are thoroughly discussed. [Copyright &y& Elsevier]