Impact of extremely cold temperatures on the safety of flameproof motors

Abstract

International requirements for flameproof equipment are contained in International Electrotechnical Commission standard IEC 60079-1. Flameproof equipment is designed so that if an internal explosion of gas or vapour occurs, it will not be transmitted to the surrounding flammable atmosphere. The standard includes two fundamental tests. The first is "Tests of ability of the enclosure to withstand pressure" which includes pressure determination and then overpressure (generally based on the maximum pressure from the previous test with a factor applied). The second is "Test for non-transmission of an internal ignition". However, there is an apparent lack of research data to clearly support some of the testing approaches, in particular where extremely low temperatures are involved. The situation becomes more complex where a phenomenon called pressure piling is involved. This is unpredictable and can lead to significantly higher pressures. Pressure piling is particularly an issue with electric flameproof motors. So the scenarios for such motors at extremely low temperatures become quite hard to predict. This thesis identifies some of the potential issues with the standard relevant to this situation, in particular when supporting data is lacking. It then reports on experiments carried out as part of the PhD project and the analysis of those experiments. The research also investigates ways to assist in predicting explosion pressures in motors based on historical data from type testing of motors, data obtained from tests carried out during this research and the potential for using Computational Fluid Dynamics (CFD). The thesis provides recommendations for changes to the next edition of the standard, information on how to improve testing processes (particularly for motors), and tools to predict likely pressures to be obtained in flameproof motors at normal and extremely low temperatures. It also identifies areas for further research.