Jun 2014
Electricity Distribution
Power Transformer Real Time Thermal Rating
Jun 2014
Dec 2016
UK Power Networks
UKPN Innovation Team
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LCN Fund Tier 1
High Voltage Technology
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 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, current summer or winter firm ratings may not be fully representative of the situation at particular sites. This seasonal increase in loading is leading to premature network reinforcement decisions.

This demonstration will be achieved by retrofitting Transformer Management System (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 Celsuis 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 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 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.