Project: 400 kV substation with heat recovery, Highbury, London (UK)
Customer: National Grid
Transformers: 3 × 240 MVA, 400/132 kV, supplied by Siemens
Ester type: MIDEL 7131 synthetic ester

As part of a 400 kV cable expansion programme across London, National Grid had to build a new substation in Highbury, a densely populated district close to the city centre. The planning authorities had to be convinced that a substation of this size could operate safely next to homes and a school – on a small footprint, with little noise and minimal impact on the environment.

The challenge

In February 2014 Siemens was contracted to supply three grid transformers on a turnkey basis, complete with a cooling system that recovers their waste heat. To keep the footprint small, the design replaced conventional free-standing radiator banks with oil/water heat exchangers, combined with water/air coolers on the roof of the transformer building. The units also had to run quietly at any load, so they were built to a low-noise design with bespoke housing and frequency-regulated fans.

Why MIDEL 7131

In an inner-city location, people and property must be protected from the risk of transformer fire or explosion. MIDEL 7131 was specified because its fire point of 316 °C is far higher than that of mineral oil at around 170 °C, which greatly reduces this risk. As a readily biodegradable fluid, it also lowers the environmental risk in the event of a leak.

The result

Waste heat from the three power transformers now heats the school next to the substation. Depending on the electrical load, more than 1 MW of heat could be recovered in future for local homes, shops and schools. Highbury shows how ester-filled transformers allow critical grid assets to be placed safely in the heart of a city – read more about MIDEL for power transformers.