Application of MV/LV Transformers with OLTC for Increasing the PV Hosting Capacity Of LV Grids

The increased use of grid connected photovoltaic (PV) systems in low voltage (LV) grids also raises concern regarding the effects of these new generation units on the grid operation. Overvoltage in LV grids during high PV generation periods is one of the well-known effects caused by PV systems, which potentially can decrease the PV hosting capacity of electric grids.

This paper presents the applications of medium voltage to low voltage (MV/LV) transformers with on-load tap changers (OLTCs) to prevent overvoltage in high PV penetration conditions. Autonomous methods for controlling the operation of OLTC during high PV generation periods are investigated and the methods are applied to an LV feeder with an MV/LV transformer equipped by OLTC located in Felsberg, Germany.

The potential interferences between OLTCs and two other overvoltage prevention methods, the demand side management (DSM) and the reactive power absorption by PV inverters, are investigated using field test results and simulations performed on the mentioned LV grid. The results show that the application of OLTC can effectively increase the PV hosting capacity of the grid.