Design of robust, safe and reliable switchgear with electro-thermal numerical simulations

Thermal management is a very important issue in medium voltage switchgear design. A temperature rise test has to be performed in order to make sure that the allowed temperature limits are not exceeded. To optimise the number of needed design tests, it is important to predict the temperature rise with a simulation tool. Sulfur hexafluoride (SF₆) gas, used widely in medium voltage circuit breakers, can produce a potent greenhouse effect if released into the atmosphere. Among the alternatives, Carbon Dioxide (CO₂) and its mixtures are considered promising. In this paper, a comparative study of thermal behaviour SF₆ and CO₂ in medium voltage switchgear is studied. Experimental investigations were also carried out to verify the simulation results and good agreement was achieved. SF6 gas exhibited the smallest temperature rise in comparison to CO₂. Additional simulations were carried out to assess the effect of conductor contact resistances, ambient temperature and increased load current levels. The simulation tool allows a number of iterative simulations to be performed in order to investigate design parameters, operating and fault conditions which are potentially difficult, destructive and costly to set up and test. Prototype materials, construction and, critically, time can reduced to a minimum by simulation. Such modelling capability is essential to ensure a safe and reliable and reliable operation of the switchgear.