Water Tree Influence on Space Charge Distribution and on the Residual Electric Field in Polyethylene Insulation

Abstract

A computation method of the electricfield and ionic space charge density in planeinsulations with water trees (using a ComsolMultiphysics software and the thermal step currents(Im(t)) measured with Thermal Step Method) ispresented. A parabolic spatial variation of volumecharge density, an exponential spatial variation ofthe electric permittivity ε and a linear dependency ofε and the temperature coefficient of permittivity αεwith the average water concentration in trees, areconsidered. For a water tree with a known length,different values of charge density are consideredand the electric field and the thermal step currentsIc(t) are calculated. The currents Ic(t) and Im(t) arecompared and the volume of charge density andelectric field for which Ic(t) is identical with Im(t) arekept.

Keywords

• insulation systems
• electric field
• space charge
• water trees