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Converter transformers play a critical role in HVDC power transmission system. Space charge is a general concern for dielectric system under DC field. In this paper, the space charge behavior in a sandwiched oil-pressboard insulation system has been investigated using the pulsed electro-acoustic (PEA) method. The presence of homo-charges in the pressboards bulk and hetero-charges at the two interfaces...
Contaminated transformer oil has been tested under non uniform electric fields and the effect of different electrode systems presented in this paper. Three different electric fields were examined i.e. DC, AC and DC biased AC. These experiments revealed that with all the different electrodes arrangements, contaminated particles were always formed bridges between electrodes under DC electric field....
The paper investigates effects of Kraft Paper to prevent bridging in pressboard fibre contaminated transformer oil. There are three different configuration of Kraft paper tested. These are 1) covered electrode with loose bond, 2) tight bond and 3) bare electrode with a paper barrier in the middle. There were no bridges formed with loosely bonded tests with DC electric fields. For the other two cases,...
Cellulose particle accumulation under AC, DC and DC biased AC electric field in transformer oil has been investigated in this paper. Different levels of particle concentrations tested with spherical electrode system. Optical microscopic images and conduction current of the particle accumulation process have been recorded during the experiments. A complete bridge of cellulose particles only observed...
Experiments were carried out on transformer oil contaminated by cellulose fibre. After the high voltage was applied to the electrodes, the pressboard particles accumulated in the highest electric field region and eventually formed a bridge. We have developed a mathematical model to simulate the bridging dynamics. The dielectrophoretic and drag forces are considered for simulation of the particles...
The effect of cellulose particles contamination on transformer oil has been investigated. Different sizes and concentration levels of cellulose fibres were used to contaminate the transformer oil for the experiments. The conduction current was measured using electrodes of 10 mm diameter with a 10 mm gap and the optical microscopic images of bridge creation between the electrodes were also recorded...
Polarization and Depolarization Current (PDC) technique is an effective tool to assess the condition of oil-paper insulation system in power transformers. So far the PDC behaviors of mineral oil-paper insulation have been widely investigated. However, with the increasing number of transformer choosing natural ester as its insulation oil, it is important to investigate the PDC characteristics of natural...
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