Technical feasibility study of Voltage Optimization Unit: Technical evaluation of distribution transformer with single phase on load tap changer for increasing hosting capacity of photovoltaic

This report provides an analysis on the benefits of a transformer with on load tap chang-ers on each phase that can be applied in the distribution system to accommodate more renewable generations such as photovoltaic power. The main purpose of this research is to verify whether power distribution transformer with OLTC per phase is necessary and valuable. The main conclusion is that power distribution transformer with OLTC control on each phase can significantly improve the PV hosting capacity in the analyzed unbal-anced scenarios. To investigate the verification problem, a simulation study is performed using the soft-wares DigSilent PowerFactory and Matlab. In this simulation study, a real low voltage network from Dong Eldistribution is modeled in Powerfactory. The measured data of the real low voltage network is analyzed and the resulting loading profiles including active and reactive power are used as load basics for the analysis. In term of PV genera-tion profiles, a realistic PV output power is assumed. Four relevant indicies such as phase neutral voltage, netural potential voltage, unbalanced factor (VUF), and power losses are evaluated in the present study. The simulation tests include two network layouts, considering a base case (passive net-work) and an active layout considering the PV integration. For each case, we compared the results of three scenarios firstly operating the network without OLTC transformer, then enabling the OLTC synchronously on three phases and finally with the OLTC act-ing independently on each phase. The simulations show that in the PV case the system hosting capacity reaches up to 105 kW for a very unbalance PV phase connection sce-nario (50% of the PV is connected on phase a and 50% of the PV is connected on phase b) and 210 kW for a less unbalanced PV phase connection (50% of the PV is connected on phase a, 30% of the PV is connected on phase b and 20% of the PV is connected on phase c), with the regulation of three single phase OLTC.