The transformer was invented 120 years ago. One of the most recent incarnations of this technology is the cast resin transformer, which Siemens has been producing for more than 40 years under the GEAFOL brand name. Unlike the oil-immersed transformer, for example, the cast resin transformer, which is a dry-type transformer, poses a reduced risk in the event of fire, since its insulating material is much less flammable. This material, which ensures that tens of kilovolts can be safely controlled within the transformer, consists of an environmentally friendly and recyclable epoxy resin-quartz powder mixture. Given their reduced fire risk, cast resin transformers are used first and foremost in places where many people would be affected in the event of a major incident, e.g. in tower blocks, hospitals, cruise liners, subway systems, and also in the Transrapid maglev train. Cast resin transformers are also very cost-effective, since they can be installed in the immediate vicinity of end consumers and, compared to classic liquid-cooled transformers, require less fire protection.

The lifetime of the insulating material depends on the temperatures inside the transformer windings. With Class F insulation materials, the average winding temperature can increase up to 100 kelvin above the ambient temperature. "That's one of the greatest causes of wear for transformers," Sorg explains. That’s also the reason why every manufacturer is always looking for ways to improve the cooling system. The more effective the cooling, the lighter and more compact is the resulting cast resin transformer. Size and weight are both decisive factors for the transformers used in almost any application - especially those involving ships and wind generators.

Cast resin transformers in essence consist of three cylinders side by side, the coils. Sorg's new cooling principle exploits the physical principle that currents of air cool quicker, the faster they move. By extending the coils upward, he has improved the so-called stack effect. He has also installed special components in the spaces between the coils, which create partial stacks in these intermediary spaces, thus also ensuring that hot air rises faster and cool air can flow in more quickly from below. "It's a very simple idea with a big effect," says Sorg. Thanks to Sorg's improved cooling system, fewer raw materials are required to manufacture the cast resin transformers. After all, the insulating materials will only tolerate a certain temperature rise. If the latter is reduced by means of improved heat dissipation, less material is required. Moreover, cast resin transformers that are already in operation can be retrofitted with the components required to induce the improved stack effect. This in turn increases their lifetime or means that they can be operated at a higher load.

Sorg and his colleagues have already demonstrated the effectiveness of the principle in experiments and prototypes. And although his quality management work currently takes him all over the world, he doesn't discount the possibility of being able to improve the cast resin transformer with further innovations: "There are still a few things that I want to further develop with," he says.

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