Pictures of the Future      Spring 2008

Power for All Climates

Siemens transformers are in service all over the world. Whether in the desert, the tropics or at the Arctic Circle—they are optimized for their locations.

A snowstorm whips across the fields in the north of Finland. Even steel high-tension cables sway in the fierce wind. The cables lead to an installation that defies even the hardest winters in the province of Oulu—less than 200 km from the Arctic Circle. At the heart of the installation is a 400-MVA transformer. While the blizzard rages outside, the 392 t colossus is transforming electricity at 400 kV to lower voltages as reliably and efficiently as it has for the last three years.

Winter temperatures here reach minus 50 °C. Ordinary steel becomes brittle at minus 40 °C, so Siemens designers rely on a specially alloyed cold-resistant steel. It would also work at temperatures below minus 60 °C, which means it could even be used in the Antarctic. The sealing materials too must be extremely resistant to the elements. "Here too we rely on very robust components," explains Project Manager Christian Ebert of the Siemens Power Distribution Division.

Since snow could fall into the fans and—in the worst possible scenario—stop the operation, the transformer fans are installed to blow from the side. Another factor is that the transformer must never be switched off during its entire service life; at the very least it can ramp down to an idle. That’s the only way to prevent it from cooling down too much.

But it isn’t only the icy temperatures that pose a challenge for the transformer’s operation and materials. Stress variations caused by temperature differences are just as critical. In summer, the sun can warm the surrounding environment up to as much as 40 °C. For the transformer oil, which serves as an insulating medium that conducts away the heat that is generated, designers use 85 t of a high-quality special oil.

Although there are many conditions to adapt to, frigid regions such as Finland have one tremendous advantage. "In principle, cold isn’t a bad thing for a transformer," says Ebert, "since transformers get very hot and have to be cooled down in any event." A low ambient temperature is in fact better for the working parts of a transformer than a high temperature, as for example in desert locations.

Surviving Sun and Sand. That’s why transformers in countries such as Saudi Arabia have far larger cooling systems. These units need a big surface area to radiate heat. In addition, special roofs protect machinery against direct exposure to the sun. Also used are radiation protection panels fitted to the sides of switchgear cabinets, allowing a gap of a few centimeters, which lets heated air rise and escape separately. Apart from heat, dust and dirt can damage machinery—which calls for the use of etched, scratch-resistant stainless steel to stand up against sand grains blasted against machinery by sandstorms.

Despite all the modifications for the widest variety of climatic conditions, basic transformer technology is much the same everywhere. "The same type of transformer is found in the desert sands as out on the tundra," says Ebert. "It is in use all over the world."  And the design type has proved to be a great success. In the far north, for instance, Finnish power utility Fingrid recently placed a follow-up order, which will be Siemens’ biggest order ever from Finland. By 2010, Fingrid wants to have five more transformers installed at various nodes in the national power distribution grid.

No matter where it is destined to go, every transformer has to undergo a battery of test procedures. This ordeal begins at Siemens’ transformer factory in Nuremberg, where machinery is subjected to days of measurements in a high-tension test-field. This can include  heating tests and lightning strikes at up to 1.3 MV. Then, when the transformer arrives at its destination, it is tested for a two-week period before it enters service.

That’s actually relatively brief, when you consider that around 18 months can elapse from the start of production (involving about 500 employees) to a facility’s actual commissioning. "But the transformer can then be relied on to supply power for far longer," says Ebert. "Assuming proper maintenance and operation is carried out, a transformer’s service life will be approximately 40 years." And that’s true regardless of how many blizzards blast across the arctic tundra, or how many times the desert is swept by sandstorms.
                                                                                                  Daniel Schwarzfischer