a groundwall insulation system for use in dynamoelectric machines carrying voltage above 4 kv , and preferably in the order of 13 . 8 kv , or higher has two layers of insulation wound onto the conductors of the high voltage winding . the first layer of insulation has a first permittivity that is greater then the permittivity of the second layer of insulation wound onto the first layer of insulation . as a consequence , at the juncture between the first and second layers there is a sharp increase in the electric field profile as seen through the groundwall insulation .