Chapter IX insulating liquids and application

The fundamental aspects related to the electric strength of n-hexane were studied further by Ward and Lewis¹. Specifically, they related such experimental parameters as air-content, prior static stress application, condition of electrodes, and relative electrode polarity to the electric strength of hexane. Measurements were performed by means of one microsecond pulse voltages, which afforded a mean pulse strength of approximately 1.5 Mv/cm. However, this was increased to 2.5 Mv/cm by use of oxidized steel electrodes and air-saturated hexane upon application of a prior static stress of 0.8 Mv/cm of opposite polarity to the pulses. A similar enhancement of electric strength was obtained when the polarities were alike but with the liquid freed of dissolved oxygen. Here, the strength is raised or lowered according to whether the static stress is of opposite or like polarity. The authors´ explanation is that the static stress sets up charge layers on the electrodes. In particular negative ion layers are formed when oxygen is present in solution. The layers modify the emission from the pulse cathode and hence, change the pulse strength.