Calculation on heating effect due to void discharge in polymers in cumulative breakdown process
The relation between PDs and the growth of the discharge channel in polymers in a cumulative breakdown process under short pulses is investigated. By comparison with the Pachen Curve, it is found that the critical size for voids to discharge is in μm class. The heat deposition on the wall of voids is also calculated with a result that the temperature rise (ΔΤ) after one discharge is in a class of hundreds of Kelvin (K) and ΔΤ under a repetition rate greater than 100 Hz is tens of K for different types of polymers. The temperature rise has two effects on the voids in polymers: one is to cause the voids to crack along the direction of the applied electric field and the other is to cause local thermal breakdowns to occur in the vicinity of the void wall. Both of these effects lead to the growth of a discharge channel in polymers. The images observed in the cumulative breakdown process of PMMA (organic glass) using an on-line microscope under short pulses are presented to support the analysis.