Influence of Electric Motors Design on Their Behaviour During Testing in Explosive Mixtures

Abstract

The research carried out in the specialized Laboratory of the National Institute for Research and Development in Mine Safety and Explosion Protection-INSEMEX Petrosani has identified the causes of high pressure peaks occurrence in the case of large electric motor enclosures as: the extremely large internal volume, the geometrical shape of motor enclosures and the very intricate and complex internal arrangement of such motor enclosures, having in mind the tendency of motor manufacturers for chemical and petrochemical industry to manufacture motors having more complex geometrical shapes. These results proved to be very useful in assisting designers of large flameproof electric motors to improve motors design so as to make them more reliable when testing in explosive mixtures.

Considerations regarding Ex d IIB + H2 method of protection for flameproof electrical equipment

“…At the high pressures achieved inside the enclosure, it cannot be assumed that the designed gap will always be maintained. Even apparently rigid constructions can flex sufficiently for the gap to open under the dynamic pressure, allowing the hot gasses to escape without sufficient cooling, and therefore allowing the external atmosphere to be ignited [10,11].…”

“…The concepts of richness and leanness apply equally to explosions as to the combustion of petrol in a car engine, with the maximum energy output relating to the "most explosive" mixture. As the exploding gasses are confined in a fixed volume, we can easily predict, for simple situations, the peak pressure [5,10,11].…”

“…For this reason, it is not usually possible to calculate pressures, but they are always determined by an actual explosion test. For complex constructions, such as electric motors, the pressures can rise rapidly and pressures in excess of 30 bar have been routinely observed [7,8,10,11].…”