Oct 2019
Electricity Transmission
Economic Ageing of Transformers
Oct 2019
Apr 2021
National Grid Electricity Transmission
Gordon Wilson
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Network Innovation Allowance
ET - Network improvements and system operability and ET - New technologies and commercial evolution
Transformers limit 38% of all circuits in the England and Wales electrical transmission network, and ultimately limit transmission boundary power flows.  Where there is a need to remove network constraints, investment in increased capacity is necessary, this project seeks to investigate whether increased capacity at the same time as allowing an increased rate of transformer ageing could be justified economically.

Transformers are rated using a tool called TRALC3, which has been developed within NGET over the course of many years (original work was conducted by the Central Electricity Generating Board).  The nameplate rating is determined on the basis of the maximum load which could be applied, under certain environmental conditions, to achieve the desired life expectancy of the transformer.  This means solving a thermal model, on the basis that the operating temperature of the insulation is one of the primary factors which determine the rate of ageing of a transformer.  For the majority of the time, the load on the transformer is less than 75% of its nameplate rating.  This means that the insulation system within the transformer ages more slowly than its standard life expectancy would suggest.  However, under emergency scenarios they can carry up to 150% of their maximum rating.

National Grid is interested in investigating methods of ‘uprating’ transformers at specific points in the network where investment is likely to replace the assets in the short to medium term, allowing constraints to be removed earlier.  This creates a more competitive electricity market and would allow National Grid to meet a key challenge, which is getting new customers (i.e. generators or major loads) connected sooner and/or with less ponderous investments in the expansion of the infrastructure.  This project seeks to investigate how this could be achieved, with a focus on quantifying the potential economic benefits that could be realised using such an approach.  This has the potential to lead to novel commercial arrangements in the future, once the underlying technical and economic drivers can be adequately assessed.
The objective of the EAT project is to determine if there are scenarios in which the use of higher transformer ratings, at the expense of the longevity of the asset, could be economically beneficial to the operation of the electricity transmission system. The project would seek to design a methodology which would allow the financial impact of different options to be assessed, with due consideration of the uncertainty surrounding actual asset utilisation. This would allow greater understanding of the economic case for providing enhanced ratings.