Various Protection Schemes for Closed Loop Feeders with Synchronous Machine Based Distributed Generation and Their Impacts on Reliability

This paper presents various protection schemes for distribution feeders in a closed loop operation. Firstly, radial and closed loop operation of conventional distribution feeders, what kind of protection schemes can be implemented for the closed loop operation and how those schemes will affect the reliability are briefly investigated. The protection schemes for closed loop conventional distribution feeders are then adopted for distribution feeders with distributed generation (DG) by taking into account the stability of the DG. Cost benefit of each scheme to the reliability of the system is investigated. It is shown that upgrading distribution feeders from radial to closed loop operation without properly upgrading the protection system will decrease the reliability of the system. On the other hand, when the protection scheme is properly upgraded, the closed loop operation will increase the reliability of the system, where the level of upgrade needed will depend on the expected reliability gain.