Online Load Flow Analysis of an Unbalanced Medium Voltage Distribution Network

The article discusses a new method for determining loads and voltages, using which it is possible to obtain reliable operational information about the state of a medium voltage distribution network. It is proposed to use the power and voltage values measured by balanced smart meters on the low voltage side of distribution transformers. This approach is especially relevant when the measurements available in the distribution network are not sufficient to ensure full observability. The use of balance meters is economically advantageous, since the cost of electricity metering points in a low voltage network is significantly lower than it is in a medium voltage network. An analysis of the mathematical models of power transformers used in Russian distribution networks with the “wye-wye with neutral” and “delta-wye with neutral” winding connection diagrams made it possible to develop a simple algorithm for calculating the loads and voltages on the primary side of transformers in a medium voltage network. As a result of the study, the factors influencing the redistribution of total loads between phases, the symmetry of phase loads, the independence of total load capacities and their losses from the zero-sequence voltage component, the load flow calculation in an unbalanced network, and network reconfiguration to minimize power losses have been determined. The effectiveness of the proposed method is confirmed by calculations using measurements performed in real distribution networks, and the conclusions derived have been verified on a physical model.