AN EXAMINATION OF THE EFFECT OF MECHANICAL-STRESS ON ELECTRICAL BREAKDOWN IN SYNTHETIC RESIN INSULATORS

A polarizing microscope with a Babinet compensator eyepiece has been used to quantify the residual internal mechanical stress in a number of synthetic resin insulators containing an embedded electrode. Markedly different magnitudes and relaxation times of the residual internal mechanical stress are found for epoxy and polyester resins. In combination with a beam bending arrangement the times for electrical tree initiation have been investigated as a function of the mechanical stress at the tip of the embedded electrode. Preliminary results show that initiation is suppressed by a compressive stress along the electrode axis, and enhanced by a tensile stress. It is also shown that a band of zero mechanical stress in the electrical breakdown region of the resin insulator can act as a substantive passivation barrier to electrical tree propagation.