Harmonic Assessment on Local Power Network for BESS Connection Through Transformer Tertiary Windings

With the increasing demands of the energy storage intake to facilitate Net-Zero in the power network, inoperative tertiary windings of existing supergrid transformers provide opportunities to connect Battery Energy Storage System (BESS). To accurately assess the impact of BESS connection on local system power quality, e.g., harmonic impact, it is necessary to conduct transient analyses with accurate modelling of the transformer. This paper aims to perform the harmonic assessment for such BESS connection application in a UK 400 kV substation and to improve the transformer transient modelling. A representative local 400 kV substation network model was modelled in ATP-EMTP. The simulation results showed the harmonic penetration in the local network is dependent on the frequency of the harmonic injection, which is related to the switching frequency of the BESS, combined by possible resonance between cable capacitances and transformer leakage impedances. In addition, a high-frequency model of a 33/0.4 kV transformer between the BESS and the connection point is developed, based on limited structural specification and one FRA measurement reference.