Oil filling - A colossal transformer

The delivery of some 390,000 litres of oil in 15 trucks arriving on a predetermined schedule, mostly in pairs and over a two-day period – that's the challenging task entrusted to Nynas as the latest of Alstom Grid's massive quadrature boosters is prepared for operation. The giant power transformer, installed at the Penwortham Substation near Preston in the northwest of England, will be filled with high-quality transformer oil from Nynas. And once the oil filling has started, the flow needs to be continuous so that the vacuum in the transformer is maintained and moisture is kept out of the system.

"There's a lot of work involved behind the scenes to ensure a project like this goes to plan," says Paul Vann, General Manager, Nynas UK. "For instance, because the particular grade of inhibited, long-life oil specified for this project meets the requirements of international standards, it is in great demand. Therefore, simply ensuring that the right oil is available locally in sufficient quantities requires good communication between all parties. Then there is the challenge of delivering this quantity of oil in a suitably dried state for processing. Nynas extended its local oil-drying capability for this type of oil solely to accommodate the throughput requirements for the quad boosters."

A quad booster is not a transformer in the traditional sense, as it doesn’t transform power. A variant of a dualcore phase-shifting transformer, it is used to control and optimise the flow in power lines and to manage the load sharing in three-phase electricity transmission networks. Quad boosters are needed because the focus for power generation is shifting from fossil fuels to renewable energy. Where historically in the UK the main power generating plants were located in the Midlands, massive wind farms are currently being built off the northwest coast. This means that parts of the power network traditionally used for power distribution now have to be upgraded in order to cope with large volumes of generated power. With 40 years of experience in building this type of unit, Alstom Grid is the only quad booster supplier in the UK and one of only a handful of suppliers worldwide. Since 1997, Alstom has supplied nine quad boosters to the UK's National Grid Company, with power ratings of up to 2,750 MVA.

"We build on average 24 transformer units per year to serve both domestic and global demand," says Mark Wilson, Head of Sales & Tendering at Alstom Grid's transformer factory in Stafford, UK. "Of these, one or two are quad boosters." The Stafford factory is Alstom Grid's Global Centre of Excellence for high-voltage transformers. The quad boosters and other transformer units built at the factory are all typically large scale. Varying in weight from 120 to 340 tonnes, the size-limiting factors for these units are the factory doors and the weight limits on roads. The transport of such large units to their final destination in the UK or to a port for delivery overseas can be tricky. "Sometimes traffic lights need to be dismantled, and between our factory and the port a roundabout has been specially designed so that our lorries can drive straight over rather than around it," says Wilson.

Alstom Grid's latest quad booster is one of the largest in the world. Measuring 10.6 x 5 x 5 metres, the quad booster comprises two sections, a shunt unit and a series unit, each weighing around 270 tonnes. Once on site, the two units are connected and engineering tests are carried out. "And then our team is pleased to coordinate and deliver the 350 tonnes of oil that's needed," says Vann.