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 u sed 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 me chanical stress are found for epoxy and polyester resins. In combinati on with a beam bending arrangement the times for electrical tree initi ation have been investigated as a function of the mechanical stress at the tip of the embedded electrode. Preliminary results show that init iation is suppressed by a compressive stress along the electrode axis, and enhanced by a tensile stress. It is also shown that a band of zer o mechanical stress in the electrical breakdown region of the resin in sulator can act as a substantive passivation barrier to electrical tre e propagation.