A transmission utility's experience to date with feeder unit protection systems

This presentation investigates a number of design, operation and lifetime management experiences of feeder unit protection systems installed on the UK's National Grid Electricity Transmission (NGET) networks. The presentation considers the policy, application design and operational experiences under the following categories in particular since the move to numeric protection: policy and application design; SDH (Synchronous Digital Hierarchy) communication networks; operational experience to date; maintenance and post-commissioning support; application of future current differential protection; and future IEC61850 applications. GPS synchronised-feeder current-differential protection has been installed on NGET UK networks since early 2000. This presentation highlights a number of problems and solutions of this type of protection, particularly NGET's experiences in the performance of GPS receivers. Finally NGET's application policy for the future installation of feeder unit protection is also discussed.