Analysis of distribution network protection issues in presence of dispersed generation

Abstract

The presence of a significant dispersed generation (DG) capacity in existing distribution systems would cause in most cases some conflicts with correct network operation. This is mainly due to conceiving a distribution system as a “passive” radial network, with neither generators operating in parallel nor power flow control. Issues such as voltage regulation, system protection, and, generally speaking, power quality are still being investigated by researchers in order to maintain adequate service to customers in presence of DG. The present paper illustrates an analysis of the relevant malfunctioning problems that may take place in distribution networks protection schemes in presence of DG. In particular, operation conflicts between distribution protection and DG are discussed with reference to unforeseen increase in short circuit currents, lack of coordination in protection schemes, ineffectiveness of line reclosing after a fault using automatic reclosing devices, undesired islanding and untimely tripping of DG interface protections. The present study aims at highlighting the need for changes, with respect to current distribution protection philosophies, which should be made by planners and distribution operators in order to increase DG penetration in distribution networks and to provide improved service continuity to customers. The presented analysis is preliminary to the development of a research project, carried out in collaboration with ENEL Distribuzione S.p.A. (Italy), which analyses possible innovative solutions for operation conflicts between distribution network protections and DG.