Thermal dimensioning of an explosion protected residual current operated circuit-breaker with overcurrent protection by the thermal network method

Residual current operated circuit-breakers with overcurrent protection (RCBOs) prevent individuals and devices from harmful residual currents and protect the connected cables from over-currents. If the RCBO is used in explosive atmospheres, an additional enclosure is necessary to protect against dangerous explosions. To ensure safe operation and functionality, the enclosure must be thermally designed so that the temperatures of the RCBO and the surfaces of the enclosure do not exceed the specified limit. The experimental proof, that all limit temperatures are not exceeded, is expensive and time-consuming. Instead the temperature distribution can be computed using thermal models. The thermal network method (TNM) computes steady-state temperature distributions faster than other numerical methods. To thermally optimize a design of a new enclosure, individual thermal network models for the RCBO and the enclosure have been set up, verified and interconnected. Using the interconnected thermal network, several parameter studies have been conducted. By the means of the parameter studies changes for an optimized thermal design were proposed. Due to the fast computations of the TNM, the optimization process is very efficient and changes of the design could already be proposed after a few days.