In recent years, the architecture of the power system has been the subject of a major change. The commonly known structure with centralized generation and one directional power flow, gives gradually the place to the new concept of the power network where both the energy generators and consumers are distributed. Particularly, the continuously increasing environmental concerns as well as the legal regulations result in a widespread installation of renewables. In addition, storage devices are incorporated in the network in order to cope with sudden increase of the generated energy. To facilitate the energy flow from the renewables towards the power network, the proper voltage level is maintained by means of transmission controllers. Such controllers consist of high frequency switching elements and the operation of such devices introduces high frequency harmonics that are propagated in the vicinity of the installed controller. On the one hand, a high content of harmonics is an emerging issue for the power network. On the other hand, some researches show the deleterious effect of high frequency signals on the reliability of electrical insulation. Finally, for many years, the harmonic content was not considered neither during the design nor the component’s testing phase. In our paper, we will firstly review the published researches regarding the influence of harmonics on the reliability of cables, terminations and transformers. Further on, an approach to model the influence of high frequency on the electric field and temperature distribution in two types of medium voltage cable termination, will be made. 1 INTRODUCTION @en