Jun 2014
Electricity Distribution
Power Transformer Real Time Thermal Rating
Jun 2014
Dec 2018
UK Power Networks, Eastern Power Networks, London Power Networks and South Eastern Power Networks
Hytham Emam
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Network Innovation Allowance
ED - Network improvements and system operability
The projects will trial Power Transformer Real Time Thermal Rating at two primary substations, 1 each in London & South Eastern licence areas of UK Power Networks. The main objectives are to:

  • Conduct extended heat run tests on representative transformers in order to clarify the variance between top oil and measured winding hot spot (WHS) temperature (where fibres are fitted) and make comparison with calculations;

  • Install Transformer Management System (TMS) equipment to gain access to key parameters;

  • Conduct tests to establish summer/winter rating with/without evaporative cooling; and

  • Develop an approved policy for implementing Power Transformer Real Time Thermal Rating

  • Develop a scalable central transformer management platform.

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.

An increase in capacity will be achieved by carrying out the following:

  • Installation of an active TMS, monitoring ambient & top / bottom oil temperatures;
  •  Installation of additional fans, modification to cooling set-points and enabling pre-cooling;
  •  Initiate pre-cooling in the event of a loss of one transformer (N-1 scenario);
  • Create an "out of firm" condition by altering network normal operational configuration; and
  • Use the TMS to ensure design limits are not exceeded and calculate impact on degradation.

A greater understanding, visibility in asset performance is expected to lead to a reduction in assets replacement, facilitating the connection of additional loads and low carbon technologies.

The main remaining risks for the project will be not being able to gain network outages to install the second TMS  equipment, the ability to carry out load transfers, and operating under N-1 conditions (close to transformer nameplate rating). The risks during the trial will be mitigated at primary substation by using load banks (which can be quickly disconnected) to supplement transformer loading. Actual network load will be used to load the transformer to remain within seasonal capacity, managing the operational risk and further mitigated by robust planning.

The following will be considered when assessing whether the project has been successful:

  • Tests to compare fibre measurements and calculations have been carried out;

  • Transformer management systems have been installed at the trial sites and performing correctly;

  • An understanding of whether an improved rating can be assigned to primary transformers has been developed.