Electrical Breakdown and Dielectric Recovery of Propylene Carbonate

Polar liquids are characterized by high permittivity and high dielectric strength. These properties make them appealing dielectrics for use in high-energy storage systems and as high-power switching media. Most of the studies on electrical breakdown and recovery have focused on water as a switch medium in pulsed-power systems. As an alternative to water, the authors have studied the breakdown and dielectric recovery of propylene carbonate (C₄H₆O ₃). One advantage of propylene carbonate over water is its relatively low freezing temperature of -55degC, which allows its use at a high altitude. The permittivity of propylene carbonate is 65, somewhat less than water (81). Its dielectric strength for pulses of 200-ns duration was measured as 2.2 MV/cm, higher than that of water (1.5 MV/cm). A nonlinear increase in conductivity above electric fields of 1.225 MV/cm, assumed to be due to field-enhanced dissociation, was recorded in both cases. The recovery of propylene carbonate is similar to that of water, with plasma decay, shock-wave emission, and vapor bubble formation, except for the very last phase, which is determined by chemical reactions: the generation and decay of polypropylene polymers. This limits the time for dielectric recovery of propylene carbonate switches to values of more than 10 ms

I. Introduction

Research into pulsed electrical breakdown in liquid applies to many fields including energy storage [1], [2], high-voltage switching [3], [4], and high-voltage insulation [5]. Notably, polar liquids have large dielectric constants and high dielectric strength [6], [7], which allow temporary electrical energy storage at high energy densities. Measurements of the dielectric strength (breakdown voltage) of polar liquids have focused on water [8] and mixtures of water with glycol [5]. For water, particularly, an empirical equation for the electrical breakdown field, which takes the pulse duration and the electrode area into account was established by Martin [9]

$$\begin{equation*}F_{\pm}=\alpha K_{\pm}A^{n\pm}\tau^{-1/3}\tag{1}\end{equation*}$$ where is the breakdown field in MV/cm, is a constant related to the electrode geometry, is the electrode area in cm ², within 90% of the peak electric field. and are polarity con-stants, given by , and . in microseconds is the effective time and is defined as the duration for which the voltage reaches 63 % of its maximum value. It was found this formula can hold for pulse durations down to 200 ns when the pin electrode is cathode. However, when the pin electrode is an anode, Martin's formula needs to be adjusted for the values of the polarity constants (from 0.23 to 0.34) and (from −0.058 to −0.09) [10]. For a point-plane electrode configuration, where the point electrode area is not a significant factor, was found to have a dependence [11].