Power quality is an issue of ever increasing importance, and with ever increasing customer expectations on such issues, the significance of supplying customers with high quality power can never be underestimated. One of the most important matters that define power of good quality is the voltage level each customer is supplied with. Most appliances are designed to operate satisfactorily only within a narrow range of supply voltages. Inappropriate supply voltages can not only result in poor performing appliances, it can also cause equipment damage, increase distribution losses and decrease the revenue for the power supplier. The point that is electrically closest to the consumers, where the voltage is actively regulated and monitored, is usually in a zone substation, where on load tap changers on the zone substation transformers ensure that the voltage in the distribution network is kept within appropriate limits. The supply voltage is therefore directly reliant on correct operation and functionality of the on load tap changers and their controlling automatic voltage regulators. The main objective that this thesis seeks to achieve is to determine the most effective method of voltage control to be utilised with different types of zone substations, primarily with respect to the algorithms utilised in the automatic voltage regulator. Metering data from the distribution network has been utilised to examine the present voltage performance of the distribution network. Different reasons that can cause voltage fluctuations and unpredictable voltage performance are investigated and discussed. Voltage levels that are investigated are steady-state voltages, hence transients, flicker, and sags and swells of short duration have not been taken into consideration. The present voltage levels are also examined in network models, with the aim to investigate the impact of altered methods of voltage control in zone substations. The accuracy of the utilised network models is also investigated, by comparing metering data to modelled voltage levels. This thesis is undertaken with the assistance of Ergon Energy Corporation Limited, a corporation owned and operated by the Queensland Government. Ergon Energy owns and operates the subtransmission and distribution network in regional Queensland. It is intended that this thesis will aid understanding of the voltage performance of the distribution network, and that it will bring clarity to how the voltage in the distribution network should be controlled in order to achieve optimum voltage performance.