For example, insulator Z has a threshold voltage of 1000V. After exposing insulator Z to more than 1000V, its breakdown threshold voltage is now 800V. Can I lower the threshold voltage further with high-voltage or can I only lower the breakdown threshold voltage once?
Here's a quote from the source material I'm reading that has me asking this question.
Many solid insulating materials exhibit similar resistance properties: extremely high resistance to electron flow below some critical threshold voltage, then a much lower resistance at voltages beyond that threshold. Once a solid insulating material has been compromised by high-voltage breakdown, as it is called, it often does not return to its former insulating state, unlike most gases. It may insulate once again at low voltages, but its breakdown threshold voltage will have been decreased to some lower level, which may allow breakdown to occur more easily in the future. This is a common mode of failure in high-voltage wiring: insulation damage due to breakdown. Such failures may be detected through the use of special resistance meters employing high voltage (1000 volts or more).
I'm mainly interested in the possibility of lowering the voltage threshold further by repeated high-voltage breakdowns as described above. I understand that different insulating materials have different properties, however I don't know enough to be anymore specific. Maybe you can provide me with an example if that would help?