Effects of Zeus 765/400kV transformer tap changer positions on system performance when overlaid 765kV lines are series-compensated

Published research findings [1,2] on the effect of tap changer position of transformer on the steady state and voltage stability performance of a network with very high voltage transmission lines operating in parallel with a well developed corridor of 400kV lines showed that the tap changer position of a 765/400kV transformer has a significant effect on the power flow, active power losses, and voltage stability limits. The study showed that in very high voltage transmission line networks, power flowing in the transmission lines and active power system losses can be made to swing within quite a sizeable range as the position of the tap changer is varied. This paper extends the work reported and investigates the effect of compensating the whole 765kV lines on the steady state (loadflow and active power losses) and voltage stability of the Cape corridor when the impedance of a 765/400kV transformer is varied with a tap changer. So, tapping transformers on a series compensated network has a huge impact on power system power flow, system losses, and voltage stability. Series compensation and tap changer position can have a huge impact on the technical and economic considerations for expansion and operation of the network.