Investigation into Protection of Active Distribution Network with High Penetration of Embedded Generation Using Radial and Ring Operation Mode

Abstract

Existing distribution networks are mostly designed to operate in radial mode without having generation units accommodated on them. The increase in penetration of embedded generations (EGs) into existing distribution network in recent years has resulted in bi-directional power flow and changes in network voltage profile. These in turn caused important impact on system protection of existing distribution network. The protection issues that have been identified include (i) increase of network fault level that requires costly upgrading of switchgears, (ii) disruption of feeder protection operation which could lead to unnecessary tripping of healthy feeders and reduction of the fault detection sensitivity of protection devices, (iii) the necessity of introducing new protection requirements particularly with regard to loss of mains (LOM) protection to avoid islanding condition (iv) the necessity of introducing the concept of intentional islanding under certain circumstances. Future distribution networks are likely to be operated in ring mode rather than radial in order to optimise the integrated capacity of embedded generations as reported in literature. The advantage of adopting ring mode operation includes, (i) increase of the reliability of electric power supplies and (ii) in the context of EGs, it eases the issues of voltage regulation. However, ring operation mode in addition to the presence of embedded generation could complicate the protection system, particularly, that related to feeder protection. Therefore special considerations are required for ring feeder protection compared to radial operation mode. This paper concerns with investigating the protection requirements of ring and radial distribution networks in the presence of embedded generations (EGs).