Investigation of oil level and type of solid insulator on creeping discharges propagating under an ac electric field

This paper presents a study on the use of different solid insulators and oil volumes inside oil-filled high voltage equipment to minimize the effect of damage that occurs due to creeping discharge activity. A point-plane electrode arrangement-based test apparatus, energized by a high voltage supply, is used for analyzing the propagation of creeping discharges over solid/coconut oil interfaces using visual observation. In particular, the effect of oil level and the effect of the kind of solid insulators, such as glass and acrylic, are analyzed incorporating the discharge length associated with pattern propagation. The result shows that the glass and acrylic insulators do not have a significant effect on the discharge length when they are immersed in coconut oil even if the breakdown voltage of acrylic is higher than that of glass by 28%. The results also show that when the oil level inside the test cell increases, the amount of ramification and propagation of streamers decreases, reducing the discharge length. The fall of the coconut oil level under electric field-generated electrodynamics motion inside the oil-filled high voltage equipment can create an opposition force on the discharge propagation. However, such a phenomenon can initiate discharge propagation at low voltage values.