Modelling and Electrothermal Simulation of Temperature Rise in a SF6-Free MV Circuit-Breaker

Active research for replacement of SF6 is more complex and requires the validation of many criteria to ensure proper operation of the circuit-breaker under normal conditions. Among these criteria, there is the temperature rise of the conductors which must not exceed a limit in accordance with the IEC or IEEE standard. After completion of dielectric type tests, it was proved that pure nitrogen at 2.5 bar can replace SF6 at 1.5 bar in a VOX 38kV outdoor circuit breaker by meeting the dielectric requirements. This article deals with the simulation of the temperature rise in different elements of the circuit breaker with these two gases: SF6 and N2. The coupling of computational fluid dynamics and computational electro magnetics and non-isothermal flow are used to determine the temperature rise of the breaker. Simulation tests were performed at rated nominal current 2000 A, 50 Hz with specifications of IEEE and IEC standards and finally, the requirements were met with SF6 at 1.5 bar whose results are in good agreement with those of the experimental tests carried out and allowing to predict the results with N2 at 2.5 bar with numerical model build. The results with N2 show a better thermal behavior of all the conductors of the breaker than with SF6 and conclude that pure nitrogen at 2.5 bar can replace SF6 at 1.5 bar in a 38kV outdoor circuit-breaker.