Protection strategies for improving quality of supply

Electricity supply quality has become an important and integral part of the utility business. Topics receiving attention include, inter alia, the incorporation of quality of supply parameters into electricity supply agreements, utility and user mitigation technologies, the development of standards and the quantification of quality of supply parameters through measurement. Voltage dips are one of the most common events on the utility power system which can adversely affect the quality of supply. The occurrence of voltage dips is costly, both to the customer and the national economy. In South Africa, the loss suffered by major industrial customers due to dips is more than R 1.2 billion per annum. This paper explores the influences of protection operation on quality of supply, focusing on voltage dips, and proposes some possible strategies to improve quality of supply through the adoption of different protection technologies, philosophies and application and setting practices. The strategies focus, inter alia, on fault clearance times, auto-reclose policies, setting philosophies and adaptive protection techniques. The paper also presents the results of a study in which voltage dip measurements over a 2.5 year period are correlated with 2624 fault events on the Eskom transmission system over the same period, in terms of the type (and hence speed) of protection employed