Efficient and Effective

Power Transformer Real Time Thermal Rating

Project Data

Start date:


End date:





The Power Transformer Real Time Thermal Rating project set out to demonstrate that additional capacity can be made available from existing assets on the electricity network by safely running transformers at higher temperatures.

What is the project about?

The Power Transformer Real Time Thermal Rating project intends to demonstrate how additional capacity can be made available from existing assets and defer reinforcement by three years or more. It is estimated that transformers can be loaded by up to 20% above static seasonal rating.

Changes in environmental conditions have a dramatic effect on transformer loading and in urban areas due to rise in air conditioning installations, historic conditions of load and ambient temperature may not be fully representative of the situation at particular sites. This seasonal increase in loading may lead to cautious network reinforcement decisions.

This demonstration will be achieved by retrofitting TMS onto existing assets to provide real-time monitoring of the transformer’s health, and continuously calculate the transformer thermal capacity, thereby safely loading the transformer close to the maximum top oil temperature less 2 Deg Celsius allowed by design nameplate.

How we’re doing it

The project will retrofit a suitable Transformer Management System (TMS) solution at sites where tight capacity margins prevail during the current price contreol period (RIIO ED1), to trial Power Transformer Real Time Thermal Rating.
The main activities will be:

  • Conduct extended heat run tests on at least one new transformer at factory acceptance test to validate variance between actual
    WHS measurements using fibres vs. calculated WHS temperatures. This transformer will be representative, but will not be identical to
    the transformers on site;
  • Real-time monitoring of key parameters at existing transformer sites: top/bottom oil/ambient temperatures, demand shape (evening peaks/cooling cycle) & load transfers;
  • Installation of additional fans (normal and/or evaporative cooling), real time loading/ageing calculations based on thermal data; and
  • Create an “out of firm” condition and ensure that design limits are not exceeded.

What makes it innovative

The RTTR project is:

  • Enabling us to load up to an extra 10-20% more capacity on transformers, saving customers money by deferring spending of £10m a year.
  • Improving safety by giving us highly accurate data on how assets are performing.
  • Freeing up 10,000KVA of additional capacity annually, enough to power a minimum of 5,000 additional homes every year without the need to invest customers money on reinforcement.
  • Advancing the transition towards an integrated, automated smart grid through data science and machine learning of real time measured & historical data.

What we’re learning

The main learning that will be shared with other DNOs is expected to include:

  • An improved understanding of transformer thermal behaviour and asset utilisation;
  • What is a safe enhanced transformer rating;
  • The required minimum specification for TMS equipment; and
  • What policies need to be developed to implement Power Transformer Real Time Thermal Rating.
thinking outside the box icon
Share your ideas

If you have an idea that could reshape or revolutionise the way we work, we want to hear from you.

Submit an idea