Pressure Rises Due to Arc Under Insulating Oil in Closed Vessel—Relationship between Bubble Behavior and Pressure Rises

Abstract

SUMMARY When a fault arc occurs in oil‐filled electric power equipment such as transformers in transmission and distribution systems, it generates a flammable gas and a dynamic pressure rise that may trigger an explosion. The purpose of this fundamental study is to investigate the effects of the arc under electrical insulation oil on pressure rises in a closed vessel containing air and oil. In particular, this paper is intended to investigate the relationship between the pressure rises and the generated bubble behavior by the arc. The pressure rises in both air and oil are measured under experimental conditions involving an arc current ranging from 2.3 kA to 8.9 kA, an arc duration of 10 ms or 100 ms. Experimental results show that the behavior of a bubble affects the pressure rises in the air and the oil as low‐frequency pressure oscillation comparatively.

Pressure Rises Due to Arc under Insulating Oil in Closed Vessel—Pressure Fluctuation of Depth Direction in Oil

“…As a result, in the experimental aspect, we found out among the other things that pressure of the air phase changes accordingly to the bubble volume in water, and that sharp pressure pulses are generated during bubble formation and destruction [4,5]. In addition, in our previous study [7], we embarked on experiments with air-oil two-phase system, and reported on decomposition gas bubbles produced by arc in insulating oil, relationship between gas-phase and liquid-phase pressure, and arc energy dependence of bubble volume. In addition, in our previous study [7], we embarked on experiments with air-oil two-phase system, and reported on decomposition gas bubbles produced by arc in insulating oil, relationship between gas-phase and liquid-phase pressure, and arc energy dependence of bubble volume.…”

“…As can be seen from the diagram, arc occurs between the electrodes as soon as conduction starts, and insulating oil around the arc instantaneously turns into a bubble of decomposition gas. In addition, as regards liquid-phase pressure at the arc depth, pressure caused by bubble behavior superimposes onto pressure rise corresponding to the bubble volume (Section 4 of the previous report [7]). This decomposition gas bubble expands and contracts repeatedly in the electrode gap during conduction.…”

“…In this way, the arc continues inside the bubble of decomposition gas comprising mainly acetylene and hydrogen. Besides, in case of 100 ms conduction time, bubble volume per unit energy, estimated from the maximum pressure rise in air phase and converted to normal pressure, was about 0.17 L/kJ (Section 5 of the previous report [7]). In this study, bubbles generated at a current of 6.6 kA are larger than the observation window; thus the images in Fig.…”

“…3, we give a summary of discussion in the previous report [7]. 3, we give a summary of discussion in the previous report [7].…”

“…4 (Section 3 of the previous report [7]). Estimation of bubble volume from these images showed that the airliquid interface fluctuates according to the bubble volume, and pressure rise occurs in the air phase due to increase and decrease of the air-phase volume (Section 3 of the previous report [7]). In this way, the arc continues inside the bubble of decomposition gas comprising mainly acetylene and hydrogen.…”