Evaluating the effect of measured power disturbances on protective relay operation

With the restructuring and privatization of the electricity supply industry, the consumer of electrical energy has a wider choice of utilities, which promise to deliver power of high quality. To depict the quality of power provided by the utilities, it is necessary to use some quantified index and criteria to evaluate the type, duration time of the disturbances, as well as their effects on equipment. This paper presents a method to quantify the effect of disturbances on a protective relay. Both solid-state and digital relays are modeled and tested under various measured disturbance conditions. The disturbance data are obtained from measurements in European distribution networks. As the effect of disturbances on protection devices is dependent on the structure and principle of a relay, a method is developed to evaluate the severity of disturbances as experienced by the relay.