Current Unbalance Calculations in Meshed Transmission System

This paper describes current unbalance calculations in example of meshed transmission system and proposes possible way of its reduction. In meshed system composed of several parts with different types of conductors, phase sequences arrangements, types of towers, and different number of lines on the same tower several computational challenges arise and must be solved. Transmission system can be composed of several parts with different number of lines, but usually with the same number of shield wires. In calculations, shield wires must also be taken into account and matrices with different dimensions are obtained. To keep the continuity of the calculations, dimensions of matrices in final matrix equations must be met and virtual shield wires must be created. Possible requirement for the calculations is meeting the nominal currents values in transmission lines caused by voltage sources connected to one side of them. Size of individual line current depends on corresponding voltage source, but also on the sizes of other sources of remaining lines. Keeping the nominal currents is an important requirement when comparing unbalance in several proposed transpositions. Possible way of obtaining required line currents is using the optimization based on Newton Raphson method. For final calculations, several input data is needed. Sometimes, the data may not be known, or depends on the topical ambient conditions and their values must be estimated. Final part of this paper shows calculation result sensitivity on the input data and its influence on the overall unbalance.