Transmission transformer tap changer optimisation while minimising system losses using security unconstrained Optimal Power Flow (OPF) techniques

Abstract

This dissertation investigates the feasibility of fixed tap or reduced tap transformers on the Eskom Transmission system, thereby reducing transformer failures and reducing the cost of new or replacement transformers. The main analysis uses Optimal Power Flow (OPF) techniques based on a Siemens PSS/E software platform and a minimum system loss operating point or objective function while reducing tap movements and maintaining prudent system limits but allowing shunt VAr devices to freely compensate for the reduced tapping. Various years and system conditions are analysed.Finally it is shown that replacing some Transmission transformers with fixed-tap transformers is a more cost effective solution. The contribution of this research is two-fold: 1. to show that there is scope for Eskom System Operations to operate its system more efficiently in terms of system losses 2. to show that an OPF methodology is a practical technique to limit transformer tap movements and allow optimal VAr placement while minimising system losses