Voltage unbalance in an urban distribution network - a case study

High levels of voltage unbalance measured at a Zone Substation in Western Sydney necessitated an examination of causes and ways to reduce the voltage unbalance in order to stay within limits prescribed in the National Electricity Rules. Network configuration including overhead conductor arrangement, loading levels, transformer parallelling and capacitor switching were all examined. Network modelling was performed to check the impact of the various influencing factors. Unbalanced load of hot-water systems appears to be the largest factor causing the observed voltage unbalance and thus a recommendation is made that load balancing should be performed. Failing that, keeping all 33/11 kV transformers in service will reduce the unbalance to allowable levels.