Abstract
The use of dielectric fluids in direct cooling techniques offers an opportunity to address the thermal demands of highpower electronics that current external-to-case methods are struggling to meet. However, limited understanding about the voltage isolation performance of these fluids under different flow conditions limits their application. This effort seeks to understand the flow-dependent behavior of dielectric fluids, specifically of HFE 7500, when applied in force convective cooling method. To help understand this behavior, the flow characteristics of the dielectric fluid flowing over a needle-to-needle electrode configuration are compared to the partial discharge behavior when high voltages are applied. First, partial discharge data is collected for different flow rates in a closed flow loop containing the test section with the electrodes separated by a gap of 1 mm. Next, the test section is slightly pressurized to measure breakdown voltage and partial discharge on the dielectric fluid. The initiation of vortices due to flow over the needle configuration past a certain flow range creates low pressure zones that periodically detach from the electrodes. These low-pressure zones could impact the dielectric strength of the fluid as seen in the increased partial discharge rate for certain flow regimes. A lower breakdown voltage of HFE 7500 is observed when negative static gauge pressures are maintained in the test chamber, further supporting this hypothesis.
