National Grid Back-up Protection Setting Tool for Grading Coordination across Distribution Network Operators/ Third Party Interfaces

Abstract

Back-up protection grading coordination across 400/132kV and 275/132kV auto transformers is essential to ensure that adequate discrimination between the National Grid and Distribution Network Operators (DNOs)/third parties is preserved. This is applicable for new transformer installations and any changes in protection settings due to changes in the 132kV network. A protection grading tool that provides grading margin checks for overcurrent and earth faults to National Grid's latest policy has been designed to provide a consistent output and increased efficiency on the demands of National Grid's internal engineering resource. This paper provides a summary of the change in policy, the algorithm adopted, an overview of the tool from the perspective of the user and a case study to show application.