scope:

PURPOSE AND SCOPE

This Technical Guidance Note presents the limits for temporary over voltages in the GB EHV network for 400kV and 275kV voltage levels.

The limits shall be used at design stages, equipment procurement and assessment of the grid performance.

Due to the nature of temporary overvoltages and their effects on equipment connected to the network, the limits are provided in two parts; the limit that applies to the changes in the instantaneous level of the voltage and the limit that applies to the changes in the root mean square (rms) of the voltage. The limit on the rms value of the voltage applies only to unplanned events.

It is required by this technical guidance note that all designs impacted or altered due to the implementation of these limits are recorded for the duration of three years from the date of publication of this document. The changes made including the parameters of TOV, i.e. magnitude and duration shall be entered in the record. System Design department, Network Engineering, ETAM is responsible for keeping the records. National Grid's System Design department shall be informed to update the records in cases where the project is managed and study is performed by other organisations.