Analysis of the dielectric and breakdown characteristics of Nano MMT modified insulation pressboard

In order to improve the breakdown voltage of oil/press board insulation structure in converter transformer, the MMT ( Montmorillonite) modified pressboard was developed by nano doping method. The conductivity, relative permittivity and breakdown strength of modified pressboard were measured. The measuring results show that the conductivity of modified pressboard increases at high nano doping ratio, and it´s obviously influenced by electric field strength. The relative permittivity of modified pressboard decreases to the lowest at nano doping ratio of 1%, which is 14% lower than non-modified ones. Moreover, the breakdown strength of modified pressboard at nano doping ratio of 1% is higher than other ratios under DC and AC voltage. Based on the dielectric characteristics of modified pressboard, the homogenizing effect of the nano modified pressboard on electric field distribution was verified hy simulation. Finally, the breakdown voltages of oil/pressboard insulation structure with modified pressboard at different nano doping ratios were tested. The results show that the DC and AC breakdown voltage can be improved in varying degrees by using the modified pressboard.