Electric Arc-Induced Pyrolysis of Transformer Oil: A Pathway to Combustible Gas Generation, Fireball Formation, and the Challenge of Visual Scale Perception in Night-Time Incidents

Abstract

Power transformers are critical components in electrical grids, and their operational integrity is paramount. The mineral oil used within these transformers serves as both an insulator and a coolant. However, internal electrical faults, particularly high-energy arcing, can subject this oil to extreme thermal stress. This article investigates the phenomenon of pyrolysis in transformer oil initiated by electric arcs, typically resulting from fault conditions with voltages such as 25,000 Volts or higher within the equipment's operational context. It explores the mechanisms by which arc-induced high temperatures lead to the decomposition of insulating oil into various combustible gases, primarily hydrogen, acetylene, methane, and ethylene. The rapid generation and accumulation of these gases can cause a significant pressure rise within the transformer tank, potentially leading to tank rupture. Upon rupture and the subsequent release of the flammable gas mixture and atomized oil into the atmosphere, ignition by the arc or hot components can result in a catastrophic fireball and sustained fire. This review synthesizes existing literature on arc characteristics, oil pyrolysis chemistry, gas generation dynamics, pressure vessel failure, and combustion phenomena to demonstrate the credible pathway from an internal electric arc to a transformer fireball. Furthermore, it addresses the common misperception of fireball size when viewed through low-resolution, low-frame-rate night-time cameras, considering factors such as blooming, lens flare, and atmospheric refraction due to humidity, which can lead to an overestimation of the actual event scale. Understanding this entire sequence, including the nuances of visual evidence interpretation, is crucial for enhancing transformer design, safety protocols, diagnostic techniques like Dissolved Gas Analysis (DGA), and accurate post-incident analysis.

Keywords: Pyrolysis, Electric Arc, Fireball, Dissolved Gas Analysis (DGA), Transformer Explosion, Power Transformer Safety, Fault Gases, Visual Perception, Image Artifacts, Night-Time Recording