Polyurethane foam insulation in line interrupters

Electrical insulation for use in high voltage switchgear is usually categorized as either gas, liquid, or solid. Equipment designers use all three materials in combinations to achieve the maximum utility at minimum cost. Since high voltage switchgear is physically large, air insulation is most often used. Oil insulation is used where compact designs requiring heat dissipating means are needed. Solid insulation is most frequently used in parallel with gas or oil except in the most simple systems, such as cable. Extending the concept of solid insulation combined with a gas insulation to the limit of combination, a high efficiency system has been attained with modern plastic foam.