Effect of the tap changer position of Zeus 765/400kV transformer on the steady state and voltage stability performance of the Cape system

Previously published research findings [1] on the impact of tap changer position on the steady state performance of distribution networks indicate that very little impact results from varying the tap changer position. In this paper, a similar investigation is carried out, but on a network with very high voltage transmission lines operating in parallel with a well-developed corridor of 400kV lines. The per-unit impedance of a line is reduced drastically as the line voltage is increased. When the design voltage of the transmission lines is high, the transformer impedance becomes dominant and plays a key role in the system. This paper investigates the effect of varying the impedance of a 765/400kV transformer on the steady-state (loadflow and active power losses) and voltage stability of the Cape corridor.