Serving low load levels by derating line voltage using step down transformers

Steady state voltage problems in power systems are those associated with undervoltages resulting from increasing loads. Steady overvoltages can also arise when loads served by networks are reduced, and the problem can be exacerbated if lines supplying load centres are long. This paper reports on a study that was conducted to assess the impact of derating voltage of lines, by using step down transformers on the lowest load a network can accommodate without overvoltages. A program written in Python and using PSS/E to perform loadflows, was used to perform analyses at various load levels. The study showed that with derating transformers installed, voltages in the system were better, there was less reactive power flow, and active power losses were lower. Derating lines using step down transformers is therefore a potential solution for serving low load levels.