The effect of hydrostatic pressure on streamer inception and propagation in insulating oil

Abstract

This paper investigates the pressure dependence of streamer inception and propagation in highly purified insulation oil (Shell Diala D) stressed with impulse and AC voltage. In a point-to-plane electrode configuration the hydrostatic pressure was varied from 0.1 to 1.5 MPa. For both polarities, the minimum breakdown voltage increases with pressure. The time to breakdown and the propagation velocity of all streamer types are pressure-independent as well as the secondary streamer inception. The most obvious pressure-dependent effect is the change of the primary streamer pattem. At atmospheric pressure the highly ramified primary streamer propagates in a sector wider than 180 degrees. With increasing pressure the sector angle diminishes and the ramification reduces.

Pressure Dependent Propagation of Positive Streamers in a long Point-Plane Gap in Transformer Oil

“…The pressure-independence of the velocities is in line with what has been observed in short gaps in various oils [1,2], and it suggests that the processes controlling the velocity must take place in the liquid phase since the oil is close to incompressible, as also observed in [13]. Since the channel is gaseous and more or less plasma-like and hence should be affected by the pressure, these processes are likely to be the electronic processes in the streamer head area which are necessary for the streamer existence in the first place.…”

“…Reduced branching with increasing pressure, with the resulting streamer looking to be more directed towards the plane electrode, has previously been observed in Shell Diala D [1].…”

“…Common to most of the available studies is a short electrode gap, for point-to plane gap and impulse voltage typically somewhere in the range 1 -7 mm [1][2][3][4][5][6][7][8][9]. While most of the work has been done in pure liquids like cyclohexane, n-hexane, toluene, pentane or cyclooctane, there are also examples of studies in transformer oils [1,2] or silicone oil [2]. Some of the work has mainly used the effect of pressure on onset for illuminating streamer mechanisms [4][5][6][7].…”

Streamer Propagation in a Long Gap in Model Liquids

“…Electron scavengers accelerate and reduce the breakdown voltage of negative streamers [2]. Increased hydrostatic pressure was seen to suppress streamer propagation and raise the breakdown voltage [8,9,11]. An increase in viscosity was seen to significantly change streamer shape and reduce time to breakdown [10].…”

“…To understand the mechanisms behind streamer propagation in mineral transformer oil, numerous studies have been performed with hydrocarbon liquids, aromatics, polyaromatics and mineral transformer oil [2][3][4][5][6][7][8][9][10]. In these studies, various experimental conditions such as additives, hydrostatic pressure, voltage polarity and gap distance were investigated.…”