When it comes to manufacturing transformers, the Siemens Energy site in Dresden has a long and successful history. Production of transformers already began here over a century ago, when the electrification of the world was still in its infancy. At the time, the objectives were of a more fundamental nature, i.e. to deliver electricity to consumers, whereas today’s efforts are all about changing the way grids operate. For the 240 employees at the factory, this means a lot of work. Plant Manager Frank Wollmann explains: “As a result of the energy transition, we are seeing a huge rise in demand for transformers, but at the same time the product portfolio is also changing. The market now demands noticeably more shunt reactors, so we will need to build plenty more of these in the future”.

Previously, factory testing of shunt reactors took place in Nuremberg. However, with the equipment weighing several tons, transport is costly and involves a great deal of work. In order to be able to meet the rising demand not only more quickly, but also more cost effectively, Siemens Energy took the decision to invest in a new test bay at the site in Dresden. In addition to the stringent technical demands that need to be met by such a testing system, one of the major challenges was that the conversion work needed to be performed without shutting down operations in the factory. But for Wollmann and his testing team, when it came to choosing the perfect partner for this challenging task, the answer was obvious – after all, this is the same site on which HIGHVOLT, the world-leading specialist in high-voltage testing and measuring technology, also has its headquarters and factory. “Globally speaking, there are only a handful of manufacturers who are even capable of building systems of such complexity”, explains Wollmann.

So, the testing experts from HIGHVOLT got to work. The first step was to perform an extensive range of preliminary investigations. What are the requirements that are placed on the test objects? What are the structural conditions like in the building? Where is space available to set up the components of the testing system whilst leaving sufficient air clearancesto the walls and ceilings? It quickly became clear that Siemens needed a very special solution. Andreas Thiede, who was the responsible Project Manager at HIGHVOLT, explains: “We normally offer our AC voltage testing systems as a container solution. However, this approach would have only got in the way of the work taking place on the factory premises.” Instead, he and his team needed to think about where they could make space in the building to house the individual components of the testing system.

For example, two old generators were brought up from the cellar so that the heart and soul of the new testing system could find space there instead – the converter system. This can be used, for example, to adjust the voltage for dielectric tests and generate the different test frequencies ranging from zero to 200 Hz. Thiede explains: “If I increase the frequency then the impedance of the shunt reactor also increases accordingly, and I need far less compensation power for testing.” To get even more out of the testing system, HIGHVOLT specially developed a so-called DC extension for Siemens. With the aid of this system, it is possible to investigate how the inductance changes under incremental increases in voltage. “Now it is possible to charge the shunt reactor with a DC current and simulate 150-percent operation – i.e. even above the power limits of our AC voltage system”, explains Thiede.

The system also includes two new matching transformers to supply the test voltage:A 123 kV transformer for testing medium-power transformers and a 200 MVA ultra-high-voltage transformer for testing shunt reactors. The latter was a brand new development from Siemens based on the design specifications supplied by HIGHVOLT and is capable of generating a test voltage of up to 360,000 V. Another central element is the capacitor bank, which has been individually designed by the testing specialists from HIGHVOLT to suit the specific requirements of this task. It compensates for the very high inductive reactive power of the shunt reactors. “Without the capacitor bank, we would have to install a gigantic generator that would take up the same space as several detached houses”, explains Thiede.

After a construction period of just 11 months, the testing system was up and running and ready for operation. The Siemens Energy employees working in the test bay were given prior training on the new system by their colleagues from HIGHVOLT in order to prepare them for working with it. Nonetheless, there was still a degree of anticipation during the first tests to see whether the system actually delivered on its promises. But it worked perfectly immediately, and Wollmann is extremely satisfied: “Particularly with a system of such complexity, this is not something you can take for granted.” Good news for grid operators as well: Siemens Energy can now offer significantly more shunt reactors – and this at attractive prices.