Properties of encapsulation materials and their relevance for recent field failures

Different encapsulation materials are investigated in terms of their PID-suppressing properties. In order to identify materials with a high potential for PID suppression, PID testing was conducted according to test protocols covering system voltages up to 1500 V and particularly long exposure times. Volume resistivity measurements at different temperatures and relative humidity are presented for the different encapsulation materials using “fresh” and aged samples to simulate relevant field conditions and to correlate with PID test results and field findings.