Sep 2013
Electricity Transmission
Dynamic Ratings for improved Operational Performance (DROP)
Sep 2013
National Grid Electricity System Operator
National Grid TO Innovation Team
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Innovation Funding Incentive
High Voltage Technology
The installed length of cable circuits on the 400kV network has increased substantially in the last decade, particularly in London but also in rural areas where it is increasingly difficult to gain consent for the use of overhead lines. Cable circuits typically have a lower continuous current rating than overhead lines due to the increased thermal resistance between the cable and the ambient environment and as such can form the overall limiting factor on the amount of power which can be transferred through a given network link. Historically, National Grid has planned and purchased cable circuits based on the required continuous rating. Emergency ratings would then be calculated based on a set preload for a given time and would typically be applied in the event of a circuit outage elsewhere on the network.

This approach provides a concise cable rating sheet as part of the CUP package which can be readily used by Network Operations. While this approach works well where the level of load to be transferred is known in advance, it provides for only a limited number of rating combinations based on a series of assumptions about the cable system thermal environment. Given the increasing variability of the UK climate, coupled with the trend towards higher generation of electrical energy from renewable sources, this may not always lead to the best utilisation of a cable asset as its true power transfer capability over periods of 24 hours or less may be under-estimated through this traditional approach.

The project aims to investigate, develop and experimentally validate methods for the calculation of dynamic (real time) cable circuit ratings within the transmission network, to investigate potential deployment scenarios for such methods within the National Grid network and to determine the potential benefits of using such systems as the penetration of intermittent renewable generation grows within the network.