Reducing unnecessary disconnection of renewable generation from the power system

Abstract

Future power systems with large proportions of embedded generation could be severely affected if several loss of mains (LOM) protection systems maloperate in response to a non-islanding condition, potentially leading to generation shortfall and stability problems. Although many papers discuss methods of sensitively detecting islanded conditions (a short bibliographical survey is included), almost no papers in the literature address the problems associated with the stability of such protection methods during and after perturbations on the network to which they should not react. The aim is to highlight the shortcomings in existing power system protection practices relating to islanding detection with a view to identifying necessary areas of improvement to facilitate the ongoing proliferation of renewable sources in active distribution networks. Existing LOM techniques are described and stability-related shortcomings are demonstrated using the results of rigorous laboratory testing of several commercially available relays. The testing scenarios are developed using a UK Generic Distribution System repository, a public domain database representing typical distribution system architectures. Recommendations relating to the setting of existing LOM protection devices are provided, along with an overview of research and development activities relating to improvements in anti-islanding protection, including a discussion of both technical and economical viability.