Legrand powers London Underground in multi-million pound transformer deal



Legrand’s power distribution business has developed a custom-specified Zucchini cast resin transformer to meet stringent London Underground requirements and supplied more than 80 units which are capable of delivering almost 12,000 amps onto lines that power the trains.

The transformers have been developed as part of a power infrastructure upgrade on the London Underground network and supplied to Ultra Electronics PMES for use in direct current rectification units.  These units convert the mains supply AC current to 750/630 volt DC current suitable for the rail power supply to London Underground vehicles. The transformers are engineered into the current rectification units by PMES who combine the Legrand products with electronic rectifiers within an enclosed unit for substation installation on the underground network.

London Underground required a 12 pulse transformer that could step down 11,000 A/C volts to two secondary output voltages of 251.6 or 294.4 A/C volts with a + or – 7.5% phase shift to enable conversion to a D/C current, and Legrand custom-engineered a transformer to meet these exacting requirements.  As no unproven products can be installed on the London Underground network, Legrand and PMES sent a 9 tonne, 3 x 2 x 3 metre transformer and rectifier set to IPH (Institut Prüffeld für elektrische Hochleistungstechnik) in Berlin for in-line testing under installed conditions to gain London Underground approval before going into full production.

Explains Stuart Fitzgerald from Ultra Electronics PMES: “Legrand worked closely with us in the design and development process of the direct current rectification units to ensure that their transformers met London Underground requirements and, as a result, we were able to create a single unit product which has been approved for use on the network.”

The units are being installed to replace rectification devices that have reached the end of their service life and the installation programme is also upgrading existing units in response to increased demand for power on the London Underground network, providing power to the trains that pass through stations including Earls Court, Moorgate, Tower Hill and Baker St. 

Comments Martyn Turner from Ultra Electronics PMES, “A reliable power supply is business critical to the smooth operation of the network. As demand for London Underground services continues to grow, a future proofed power supply that will meet our requirements both now and in the future is essential.  The programme of direct current rectification unit upgrades is central to delivering this goal.”

Key Facts

The project: London Underground network

The solution: Legrand Zucchini custom engineered transformers have been supplied as part of a power infrastructure upgrade on the London Underground network