Development of electrically insulating pipe sections for two-phase cooling of electrical and power-electronic devices

Insulating pipe sections from epoxy and ceramic are presented for use in two-phase cooling systems, where the evaporator is on electric potential whereas the condenser is on ground. For the example of 2 kV system voltage and 12.6 kV impulse voltage, a dimensioning procedure is presented, taking into account air, solid insulation, and refrigerant. The latter must be considered in vapor, liquid and two-phase state. Field grading is applied and shown to be effective by numerical simulation. The insulating sections are successfully verified by experimental testing. The field grading is found to have no advantage at the chosen voltage, but is expected to be important at higher voltages.