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Nowadays, power quality is a challenge for the distribution companies since the new energy policies are directed to a distributed generation system with power electronic based technologies. The reduction of distribution transformers capability when supplying nonsinusoidal load currents has a major impact within capacity reduction in distribution networks produced by technical losses. IEEE Std C57.110-2018, EN-50464-3 and EN-50541-2 define procedures to derate transformers when supplying nonsinusoidal load currents. The aim of this paper is to compare these procedures through a real case distribution transformer that suffers problems due to high levels of current distortion.

The ongoing energy transition has changed the architecture of electricity networks in ways that conventional power transformers are not able to cope with the new required functionalities. For this purpose, the solid state transformer (SST), which comprises state of the art power electronics with galvanic isolation to interconnect two separate alternating current (AC) or direct current (DC) power grids, is considered to be the dominant solution. The purpose of this paper is to provide a practical, application-oriented review of the SST. In this context, the main functionalities and possible applications of the SST are presented, including smart grids (SGs), data centres, railways, offshore wind farms, etc. Furthermore, the main developed SST prototypes are analysed with special focus on the related projects, demonstrators, stakeholders and rated values, e.g., voltage, switching frequency and power. The analysis is concluded with the future trends and challenges regarding the wider implementation of SST technology in the electrical grid.

Fault location can help transport and distribution system operators in their effort of minimizing supply interruption times. Nowadays, fault location devices are widely extended in the transport grid. However, the application of these solutions to distribution networks is not a feasible option due to the high cost of this equipment. Therefore, current research is focussed on costeffective fault location techniques which are adapted to electrical distribution networks. This paper presents results of a case study, conducted with detailed simulation models of two actual low-voltage (LV) distribution grids, using PSCAD software. One is a typical rural grid with long aerial lines, while the other is a typical urban grid with shorter line lengths which are mostly installed underground. The analysis is focussed on fault location based on travelling wave theory and reflectometry methods. The simulations include distributed parameter line models and a signal injector, in order to analyse the singular effects in the waveform which are caused by the special features of the LV network. It is shown that LV networks have some unique features which are not present in medium and highvoltage grids, which makes effective fault location more challenging. Observed issues are discussed and future work is proposed in order to overcome some of them.

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