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: Shell 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 Shell MIDEL 7131

In an inner-city location, people and property must be protected from the risk of transformer fire or explosion. Shell 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. Its ester base oil is readily biodegradable according to OECD 301 and biodegrades faster than conventional mineral oil.

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 Shell MIDEL for power transformers.