Dielectric Properties of Phase Change Coolant for Flexible HVDC Converter Valves

With the development of VSC-HVDC converter valve in the direction of high voltage, large capacity, high integration and small volume, the heat dissipation problem has become the bottleneck of improving power and frequency. As a new type of cooling technology, phase change cooling technology has become an effective cooling method for converter valves in high heat flux scenarios by taking away heat with the latent heat of vaporization of phase change coolants. As the key material of phase change cooling technology, the dielectric properties of phase change coolants comprehensively reflect the polarization behavior of dielectric in alternating electric field, which has an important influence on the uniformity of electric field distribution and energy efficiency in cooling system. In this paper, the dielectric properties of RZHLF-01 and RZHLF-02 in the frequency range of $1 \mathrm{~Hz}-1 \mathrm{MHz}$ and the temperature range of 0 $55^{\circ} \mathrm{C}$ were studied. The polarization characteristics of the medium under the action of alternating electric field are analyzed, and the influence mechanism of electric field frequency and temperature change on the dielectric properties of the cooling medium is revealed. The research is of great significance to optimize the selection of phase change coolants and improve the efficiency and stability of phase change cooling system.