Voltage Fluctuations of Battery Storage Systems Providing Fast Frequency Response Services in the UK

Within the UK there has been a significant increase in large scale Battery Energy Storage Systems (BESS) that provide services such as Fast Frequency Response (FFR) to National Grid ESO, for the GB system. At present, BESS units are installed by developers at substations with spare capacity, and their size and locations are not being centrally planned, and due to network connection costs, most developers are connecting the BESS units to the distribution network rather than to the transmission network. A concern has been identified that during FFR operation, multiple BESS units in an area would all operate nearly simultaneously, leading to large dynamic power swings in the systems creating problems for voltage Quality of Supply (QoS). This paper examines how the simultaneous operation of multiple BESS units in adjacent substations, can create adverse effects on the distribution system voltage that may not be apparent when considering operation of BESS units individually. The paper develops a simple test network which is representative of two substations on the Distribution Network in the UK; then uses DIgSILENT Powerfactory to examine the system voltage profile for BESS operation for several import-export and export-import cases.