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Electronic devices can be damaged in an undesirable manner if the junction temperature achieves high values in order to cause thermal runaway and melting. This paper describes the mathematical model to calculate the power losses in power semiconductor devices used in bidirectional rectifier which supplies a resistive-inductive load. The obtained thermal model can be used to analyse the thermal behaviour of power semiconductors in steady-state conditions, at different values of the firing angle, direct current, air speed in the case of forced cooling, and different types of load. Also, the junction and case temperature of a power thyristor have been computed. In order to validate the proposed mathematical model, some experimental tests have been performed. The theoretical values are in good concordance with the experimental data and simulated results.

In many industrial applications high breaking capacity (HBC) fuses are used to protect electrical installations against overcurrents, especially in the power distribution network. At high rated current, HBC fuses have more parallel fuselinks mounted inside. The technological and mounting processes of the fuselinks inside the fuse results in an asymmetrical current distribution through the parallel fuselinks. In this article a model of a high breaking capacity fuse using two parallel fuselinks is proposed. The influence of electric current, cross-section of the notches, distance between notches and current imbalance through fuselinks on the maximum temperature rise of both fuselinks, has been investigated. Also, a 3D thermal model for the same HBC fuse has been developed. The temperature spread into the fuse and its elements has been obtained. In order to prove the validity of the mathematical and 3D model different tests have been considered. The experimental, simulation and computed results give similar values and it results that this model can also be used for fuses with many parallel fuselinks and it permits the design of new fuse elements with optimal thermal distribution.

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