Dielectric study of water/methanol mixtures for use in pulsed-power water capacitors

Abstract

Large pulsed-power systems normally use a solid capacitive primary storage and a water capacitor for secondary storage. It is shown that the electrical breakdown strength is increased and the maximum storage time is enhanced from the microsecond level to the millisecond level when the water is replaced by a water/methanol mixture. The increased time scale in the second storage enables the use of an inductive primary storage. The mixing of methanol in the water decreases the relative permittivity. However, due to the increased electrical breakdown strength, a higher energy density is nevertheless possible. Previous work with water/ethylene glycol has manifested the problem of charge injection that occurs when energy is stored for millisecond time scales at high electrical stress. Water/methanol mixtures show less tendency for charge injection and a better ability to store energy at millisecond time scales.