Dynamic Ratings for improved Operational Performance (DROP)
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.