NG DH 28 PDF

PURPOSE

The purpose of this document is to give guidance on the application of system data (i.e. OHL Impedance and Fault Levels) for use in the calculation of protection settings.

Historically system data had been supplied on an annual basis for use in protection relay settings calculations. This data was produced using the network modelling tool ‘ELLA' which at the time was the tool used within National Grid. Around 2008/2009 National Grid began the transition away from ELLA as they began to use a new program ‘Power Factory' developed by the German company DIgSILENT. During the transitional period, an agreement was made that the Network Modelling Team within National Grid would provide system data on upon request from Technical Assurance.

Following several years of transition National Grid is now in a position where Power Factory has been fully embedded, and will once again publish system data on an annual basis. The system data is now available on National Grid's Livelink system, and this document provides guidance on where the data is obtained from, what the data represents and how the data should be applied with respect to National Grid's suite of Policies & Procedures.