A partial heat exchanger system (oil side) will be installed on a de-energised transformer at the Deeside Centre for Innovation to demonstrate that such a system can be retrofitted to in-service transformers without compromising the transformer’s cooling system and thereby affect its normal operation. The trial will determine how to install the system in such a way that both the transformer and the heat exchanger system may be accessed and maintained safely. A control system will be developed for testing purposes and integrated with existing controls.
The benefit of this project will be to demonstrate that waste heat generated from transformers can be used to support district heat networks close to transmission substations and reduce emissions of carbon dioxide that would otherwise be emitted in producing the necessary heat.
Benefits
The benefit will be achieved through reduction of carbon dioxide emissions resulting from capturing waste heat rather than generating the heat using gas or electricity to feed into a district heat network. The benefit calculations are based on the avoided emissions of installing the system compared with another source with an estimated carbon intensity of 67 gCO2e/kWh over an expected life of a heat exchanger system of 25 years.
It has been estimated for an exemplar installation for a district heat network making use of waste heat from transformers that the avoided cost of emissions has a benefit of £14.8k per annum. Making conservative assumptions about the number of installations and when they might be commissioned over the next 25 years, the total net NPV is £1m.
An assessment of the cost of installing waste heat recovery on transmission transformers compared with not installing it and sourcing the heat elsewhere has not been carried out by NGET and is assumed to be comparative.
Learnings
Outcomes
The report on the impact of heat recovery where the oil temperature is controlled as part of the control scheme showed that:
- The lifetime reduction for heat recovery using a 70 °C top oil/heat recovery temperature is negligible in comparison to the expected lifetime of the transformer.
- There is a modest increase in winding losses at a top oil temperature of 70 °C, but this increase is approximately halved if the top oil temperature setting is reduced to 60 °C and becomes negligible when the setting is 50 °C.
- Noting that these results were obtained using loading from a single site in London over the course of 1 year.
Installation of the retrofitted heat exchanger system has shown that:
- Following careful procedures for hotworks on existing transformer pipework it is possible to tee in a new pipe without introducing metallic particles.
- A well-designed heat exchanger system may be installed within an existing bund, with provision for access to the existing cooling system on the transformer.
Recommendations for further work
None at this stage.
Lessons Learnt
Innovation projects involving design elements requiring design assurance should start with the assumption that the normal assurance processes should be followed as part of the project and modify this to fit the innovation project as appropriate. Including additional steps later adds delay and cost once the project has started.
Risk assessment of projects should consider loss of key personnel, especially those in safety critical roles such as taking responsibility for assessing risk assessments and method statements (RAMS), so that appropriate mitigation plans can be made. This should include setting a new start date that is credible rather than hopeful.
Dissemination
The work carried out by The University of Manchester looking at heat recovery systems and their impact on transformer ageing will be disseminated at UHVNet 2024 at University of Exeter in May. A paper entitled “Effects of Heat Recovery on Electrical Losses and Thermal Ageing of Power Transformers” has been submitted for presentation at IEEE International Conference on High Voltage Engineering and Application (ICHVE), Berlin, Germany in August 2024. An article on the subject is planned for IEEE Electrical Insulation Magazine.
