ABSTRACT
The properties of the insulation systems of HV electric machines, forming their integral part, significantly affect their reliability and serviceability. Insulators must have good mechanical, thermal, and chemical properties in addition to good electrical insulation properties. The electrical strength of gaseous insulators is determined by the degree of their ionization. Liquid insulators generally have a higher electrical strength than gaseous insulators, but their electrical strength strongly depends on their purity. The electrical strength of liquid insulators depends on many random and almost uncontrollable parameters. The energy of the individual potential pits changes and the particles begin to overcome the potential barrier in places with the lowest energy demands. This leads to an uneven distribution of charge, the formation of a dipole moment, and thus polarization. The electrical insulation properties of insulation systems are most affected by mechanical stress, heat, electric field, and oxidation.
