Protection and Earthing Requirements of Low Voltage AC and DC Distribution Networks Interfaced by Smart Transformers

Abstract

Electrification of more transport and heat will place increasing demand on LV networks for which they have not been designed for. This can potentially overload MV/LV transformers and LV cables, and may result in voltage drops outside statutory voltage limits. Deployment of solid state smart transformers (ST) at secondary substations has recently been considered as an alternative approach to address such issues. However, their deployment will lead to a radical change in the operation of associated LV networks and, in particular, protection systems. Therefore this paper investigates in detail the impact of a smart transformer deployment at a secondary substation on the performance of conventional MV/LV protection, and provide recommendation on suitable earthing and protection for LVDC and hybrid AC/DC distribution networks interfaced by a smart transformer.