Enhancement of Gas Flow Simulation of Internal Arc in Medium Voltage Switchgear

Abstract

Internal arc in a switchgear is a rare phenomenon in its entire lifecycle. Though the mean time to failure is high, using new materials, improved production technologies or sensors for predictive maintenance, the risk of an internal arc persists. Unfortunately, the effects of internal arc are destructive and very harmful due to severe pressure rise and hot gas expulsion, which can endanger an operator or damage a property. Architecture and design of medium voltage switchgear is qualified upon the requirements of existing standards. General study across the labs indicates that a success rate of about 70% is achieved during the initial stage of internal arc validation. Data from labs reveals that the most prominent failure mode during internal arc testing is burning of indicators due to hot gas expulsion. The physics of the internal arc phenomenon is studied and employed to build the model in simulation software package using fluid dynamics numerical method. Qualitative as well as quantitative prediction is carried out, to estimate the gas flow behaviour. Firstly, the volume of the hot gas cloud and secondly the energy incident on the indicators are determined. Results are compared with data collected from series of internal arc tests with high-speed video and actual measured parameters. Based on the findings, the simulation methodology is formulated which will provide input to improve the design of switchgear. The paper presents results of recent research activity, with the objective to increase robustness of the switchgear design for internal arc performance. The prediction of burning of indicators remains a difficult task due to the complexity of all involved physics, their coupling and correct representation in a simulation model. The enhanced method presented in this paper can significantly increase the success rate during tests and ultimately safety of the switchgear and its variants.