Re: problem on insulator
When the insulator has uniform structure and the field is uniform also, you only need to consider additional dissipation due to the higher loss per volume (dielectric loss). Note that with increasing temperature, dielectric strength reduces.
When field distribution is far from uniform and/or insulation is non-uniform and dielectric strength is also non-uniform across the insulation, it becomes more elaborate. Think of insulation with air voids or contaminants, or cable insulation where there is air between the insulated wires making up the cable.
Here partial discharge (within solid insulation, in air, or over surface) may dominate the design process. Partial discharge (PD) may erode the insulation resulting in failure. The voltage where partial discharge stops (PD extinction voltage) drops with increasing frequency (compared to 50/60 Hz). A transient signal/pulse may initiate PD and that PD can be maintained by the working voltage.
If your question is related to safety insulation, you may try to get IEC 60664-4 or a product safety standard that incorporates partial discharge at > 30 kHz.