Pyrolysis and temperature characteristics of the gas produced by power-frequency arc in transformer oil

Abstract

Oil-immersed transformers are widely used in power systems. When an arc fault occurs inside a transformer, the surrounding oil is rapidly pyrolyzed. These high-temperature, flammable gases are compressed into a high-pressure bubble, which is likely to cause tank deformations, explosions, and fires. Currently, related simulations on tank internal pressure and transformer fires are based on a constant gas composition, a constant gas production rate of 0.1 L/kJ, and a constant bubble temperature of 2000 K. This paper deals with a case of a power-frequency arc (5 kA, 30 mm, 80 ms) in transformer oil. The time-varying characteristics of pyrolyzed gas production, composition, and temperature are experimentally investigated. The percentage of hydrogen changes considerably, decreasing from 85.2 % to 70 %. The overall gas production rate increases slowly from 0.0574 L/kJ in the first 2.5 ms to 0.0982 L/kJ in 80 ms. The local temperature inside the main bubble (30 mm from the arc) decreases gradually from 2200 K to 1400 K, while the average bubble temperature decreases from 2550 K to 550 K. This case and these results provide an experimental basis for the parameter selections in the simulations about transformer internal pressure and fire progression.