Evaluation of overhead lines current unbalance in meshed grids and its reduction

Abstract

This paper describes new methodology in the current unbalance calculations in meshed grids. The meshed grids, mainly the transmission ones, consist of more parts connected together which are formed using different conductor types, phase sequence arrangements, tower constructions, and various number of lines on the same tower. Therefore several computational challenges arise in comparison with the widely discussed point-to-point configuration. The methodology divides the grid into a number of impedance matrices respecting all the self and mutual impedances among all conductors and all parallel lines. Another challenging issue for the lines impedance description is changing the number of shield wires along the line if the line is composed of several sections with different tower configurations. For the current unbalance calculation, shield wires must also be included in the algorithms, and matrices of various dimensions can be obtained. For the overall matrix description to be used, dimensions of all matrices in final equations must be equal, and therefore the virtual shield wires are created. To compare more conductor transposition cases with each other, the line loadings caused by voltage sources should be equal. This is necessary mainly in case of meshed grids where the supplying sources on different lines can have strong mutual couplings. This can be achieved by an appropriately designed optimization of the connected voltage sources.