Factors Influencing the Determination of Maximum Surface Temperature for Explosion-Proof Luminaires

Abstract

Explosion-proof equipment must be designed so that the ignition of the surrounding explosive atmosphere to be avoided. This is very important because an explosion can have particular implications over goods, life and not least over the environment. One of the ignition sources of an explosive atmosphere is represented by hot surfaces. Each equipment designed to operate in explosive atmospheres develops a maximum surface temperature. The specific standards used to assess explosion protection characteristics cover only indirectly and in part the factors influencing the maximum surface temperature. By this study, using a standardized testing methodology, the factors influencing the maximum surface temperature in case of explosion-proof luminaires with type of protection flameproof enclosure "d" and increased safety "e" were pointed out and analyzed (i.e. maximum designed ambient temperature of the luminaire; placement of temperature sensors to capture the points where the maximum surface temperature is recorded; type, power and size of the light source installed in the luminaire; operating position of the luminaire; supply voltage of the luminaire). The measures to be taken, in order to determine as accurately as possible the maximum surface temperature, in relation with the influencing factors, were also identified.

The test method used to determine surface temperature for Ex equipment certification

“…After testing on different luminaires equipped with different types of light sources, there are identified a number of factors that influence the maximum surface temperature, namely [10]: -maximum ambient temperature to which the luminaire is designed to operate; -placement of temperature sensors to catch the points where the maximum surface temperature is recorded; -supply voltage of the luminaire; -operating position of the luminaire.…”

“…To minimize errors caused by the influence of light radiation on temperature indicators, a very reflexive thermal insulation material is used to protect the lead wires of the thermocouples, or another method is to use a white (or reflective) thermo-conductive paste. This is intended to minimize errors caused by the influence of light radiation, as well as to obtain a thermal contact with the area where the temperature is measured [10].…”

“…The temperature is monitored by a data acquisition system Agilent 34970A with thermocouple type J. When thermal equilibrium is reached, the output of power supply is turned-off, and the corresponding data, electrical parameters during the test are saved on PC [10].…”

Summary of requirements for the use of cells and batteries in potentially explosive atmospheres

“…The spark ignition [1] is caused by electrical equipment, electrostatic discharges and mechanical impact. The mixtures of air with flammable substances could be ignited also, by hot surfaces [2].…”

Importance of training the personnel performing specific activities related to equipment / installations operating in areas classified as with potentially explosive atmospheres

“…Even if equipment is provided in accordance with ATEX Directive 2014/34/EU provisions, the special characteristics providing protection to explosion can be invalidated during the different stages of an installation (design, erection, operation, inspection, maintenance or repairing) [4,5].…”