Impact Analysis of CVR on Distribution System Protection Scheme

This paper aims to investigate the impact of the Conservation of Voltage Reduction scheme (CVR) on a typical protection system of distribution systems (DS). CVR is an energy-saving scheme in which the bus voltages of a DS are maintained in the lower 5% range of the rated value. Changing the operating condition of a DS may have a significant impact on the deployed protection system. It has been observed that maloperation of protective devices is more frequent than the occurrence of a genuine fault. Such a condition arises due to the occurrence of any such event that has not been taken into consideration while designing the protection problem formulation. In this paper, the CVR scheme has been deployed by regulating the taps of OLTC governed by the Line Drop Compensation (LDC) scheme and switching action of Capacitor Banks (CB) to maintain the bus voltages at the desired levels. Whereas the protection objectives have been accomplished by determining optimal settings of the deployed directional overcurrent relays (DOCR) in the DS. A protection objective reassures the reliable functioning of the protective devices by determining optimal operating time and proper coordination among the relays. The protection problem formulation is non-linear programming (NLP) in nature and solved using Nature-Inspired Algorithms (NIA) based Particle Swarm Optimisation (PSO) optimisation technique. The study has been performed on the IEEE 13 node test feeder and distribution portion of the IEEE 14 bus system. The test systems have been modelled on the PowerFactory software by DIgSILENT to deploy the CVR scheme and the relay actions. Furthermore, the optimisation problem has been solved in MATLAB. Although the CVR scheme comes under the planning and operation aspects of distribution systems, its impact on the performance of protection infrastructure cannot be ignored as the effects of both phenomena come hand in hand, and the same has not been discussed in the literature yet.