Review of Dielectric Behaviour of Insulating Liquids

Insulating liquids are widely used in high voltage technological applications including power transformers, circuit breakers and components of pulsed power systems. The breakdown strength of insulating liquids is a key factor which should be taken into account in the design of high voltage systems, and as a result the dielectric properties of these liquids have been intensively studied for many decades. A significant number of research papers published in recent years are devoted to different aspects of the breakdown and breakdown behaviour of dielectric liquids, including the formation of pre-breakdown cavities and streamers, the propagation of streamers, the behaviour of pre-breakdown currents, polarity effects, and the effects of different electrode topologies. However, it is difficult to find any systematic analysis of breakdown properties of the dielectric liquids stressed for either conventional 50/60 Hz AC or DC voltages, or for fast high voltage impulses with rise time shorter than I mu s. Such "fast" high voltage impulses with magnitudes higher than I MV are employed in different pulsed power applications, for example for the generation of powerful X-rays or hot plasma. This paper is focused on a literature review of the dielectric properties of available insulating liquids such as mineral oils, bio-degradable oil and synthetic ester liquid under conditions applicable to the power industry and new compact pulsed power systems.