Study On The Influence Of Moisture Content On Flow Electrification Characteristics In Converter Transformer

Converter transformer is an essential equipment in HVDC transmission system,which can achieve the function of converter and AC bus connection,and its reliable operation is very important for HVDC transmission project.Converter transformer in addition to withstand the AC voltage,but also to withstand the DC and AC/DC superposition voltage,so the flow electrification phenomenon in the converter transformer compared with ordinary power transformer is more complex.Moisture content is an important factor to affect the safe operation of converter transformer,in order to study the influence of moisture content on the flow electrification phenomenon in the converter transformer,the primary research is as follows.To establish and perfect the oil-pressboard insulation flow electrification test equipment in the laboratory,the experiment research on the influences of moisture content on flow electrification characteristics of oil-pressboard insulation,the oil flow electrification under DC,AC and AC/DC superposition voltage at different moisture content with the typical plane oil-pressboard insulation structure were respectively measured,the theoretical model of oil flow electrification was established,the influence of moisture content on flow electrification under different external voltage type,and the influence of external voltage amplitude,velocity and temperature at different moisture content on oil flow electrification was analyzed and related expression was calculated.The experiment results show that the streaming current decreases with moisture content when without external electric field,and the streaming current increases with temperature and oil flow velocity at different moisture content when without external electric field.The moisture content has a significant effect on the streaming current when with external DC electric field and AC/DC superposition electric field,the streaming current increases firstly then decreases with moisture content at low temperature and low excited voltage,and the streaming current decreases with moisture content at high temperature or high excited voltage;The streaming current increases with external voltage amplitude,oil flow velocity and temperature at low moisture content,the streaming current decreases first then increases with external voltage amplitude and temperature at high moisture content,and when the external voltage amplitude reaches a certain extent,the streaming current decreases with oil flow velocity.The streaming current decreases with moisture content when with external AC electric field,and the streaming current increases with oil flow velocity and external voltage amplitude at different moisture content.The comparison research results show that the theoretical model of flow electrification can better explain the experimental phenomena.