Derating line voltages to limit steady overvoltages and enhance network operational efficiency

Under light loading conditions of networks, steady overvoltages can result. This is because at low loading there is not enough consumption of reactive power generated by the lines, with the consequence that excessive capacitive current flows in the system, and active power losses become high. Ultimately, this leads to increased costs of supply which have to be borne by customers. In this paper the authors have investigated the feasibility of using step down transformers in derating operating voltages of lines in a load centre as a potential solution for resolving overvoltages. These transformers are placed at the ends of a corridor, thereby derating the operating voltages of the lines between them. Loadflows were carried out for cases without (Case A) and with (Case B) the step down transformers. The inclusion of step down transformers showed a decrease in the reactive power flow in the lines, lesser steady voltages, and a reduction in active power losses. The proposed use of step down transformers is thus a feasible solution for solving steady overvoltage concerns and should be considered among other options when such problems arise.