Optimal PV Allocation & Minimal tap-Changing Transformers Achieving Best Distribution Voltage Profile & Minimum Losses in Active Distribution Networks

In distribution systems, voltage levels of the various buses should be maintained within the permissible limits for satisfactory operation of all electrical installations and equipment.  The task of voltage control is closely associated with fluctuating load conditions and corresponding requirements of reactive power compensation. The problem of load bus voltage optimization in distribution systems that have distributed generation (DG) has recently become an issue. In Oman, the distribution code limits the load bus voltage variations within ±6% of the nominal value. Several voltage control methods are employed in active distribution systems with a high share of photovoltaic systems (PV) to keep the voltage levels within the desirable limits. In addition to the constraint of targeting the best voltage profile, another constraint has to be achieved which is the minimum loss in the distribution network. An optimised solution for voltage of load busses with on-load tap-changing (OLTC) tarnsformers and PV sources is presesnted in this paper. This study addresses the problem of optimizing the injected power from PV systems associated with the facilities of tap-changing transformers, as it is an important means of controlling voltage throughout the system.  To avoid violating tap-changing constraints, a method is depicted for determining the minimal changes in transformer taps to control voltage levels with distributed PV sources.  The taps of a range + 5 to -15 %, can be achieved by tap-changing transformers. The OLTC operation was designed to keep the secondary bus within the voltage standard for MV networks.