Growth of electrical trees in solid insulation

It is shown that electrical trees in solid dielectrics grow as a result of the explosive effects of localised breakdown at points of electrical stress concentration. Tree growth is sensitive to applied mechanical strain and to internal strain built up owing to prolonged exposure to vibrational electrostatic forces. It is concluded that the ability to withstand fast crack propagation should be added to the list of factors involved in the choice of insulating materials. Also, when designing insulating systems, areas of mechanical stress concentration must be avoided.