Coordinated operation of a grid scale energy storage system with tap changer for voltage control on primary substations

Abstract

On-Load Tap Changers (OLTC) are used by Distribution Network Operators (DNOs) to regulate the output voltage of transformers and thus manage the voltage at grid and primary substations. An Energy Storage System (ESS) is equipped with power electronics interfaces which are capable of supporting the voltage control in different network points while delivering ancillary services in parallel to the electricity grid.The aim of this paper is to propose an alternative scheme of voltage control which uses reactive power from an ESS, optimising the utilisation and thus extending the life of OLTCs used on distribution networks. The proposed ESS Co-ordinated Voltage Control Service (CVCS) has been developed and assessed in a real 6MW/10MWh ESS connected on the secondary (11kV) side of an HV/MV substation in the UK.The trial results showed that a grid scale ESS is suitable and effective in providing voltage support across a full load cycle (24 hours), while allowing a lifetime extension and maintenance deferral of OLTC’s in primary substations.