Pre-feasibility investigation into converting fixed line reactors in the Cape system into variable types

To supply the Eskom's Western Cape portion of the transmission grid, a mature system of 400kV lines, in parallel with 765kV lines, is used. These lines move power from Mpumalanga in the northern part of the system, where a generation pool of coal-fired power stations is located, over a distance of about 1500km, to supply the loads. The above-mentioned transmission lines were designed with fixed line reactors, to protect them from being damaged by high voltages in case of fast and substantial voltage rises, e.g., due to sudden loss of load. The reactors installed in the power system consume capacitive reactive power from the system, and this can have adverse impact on the performance of the power system, e.g., problems in maintaining voltages within acceptable levels, adverse impact on total active power losses of the system, and adverse impact on the voltage stability margin. By making these reactors controllable, it will be possible to inject least amount of reactance required during peak conditions to ensure maximum performance, and to insert maximum reactance needed to operate the system during conditions of least loading. In this paper, the results of a preliminary investigation into converting the fixed line reactors in the Cape network into controllable type are presented.