Transformer plant in Nuremberg: the making of a vehicle transformer

The production of vehicle transformers requires expertise, precision and an efficient process. After all, numerous production steps are necessary to build a powerful vehicle transformer from the raw materials. Our Traction Transformer Teams made up of members from the areas of processing, production, coils, assembly and testing ensure that quality is maximized at every step.


A software program has been developed specifically for calculating the transformers. This software is continually monitored on the basis of the values measured in the test bay and the previously calculated values. Design and modeling are carried out entirely using a 3-D CAD system. The design data are then also available for integration into the complete system as well as for testing the mechanical interfaces. As needed, specific customer and system requirements are also met through joint efforts between internal Siemens experts and external experts from universities.


At the plant in Nuremberg, the entire flow of materials is optimized for throughput, from the receipt of goods to dispatch. As a result, all processes are seamlessly interlinked. Core processes are carried out by Siemens employees on production lines set up for this purpose; these processes include the production of cores and coils, pre-assembly and final assembly, as well as testing and preparation for shipping. All employees are highly trained, experienced and very motivated. The portion of skilled employees is over 90 percent. All processes are subject to constant quality testing. This ensures that every transformer is manufactured according to specification and tested according to the inspection and test plant.

Processing transformer magnetic sheet steel

One of the first production steps is processing of the transformer sheet steel. We process approx. 7,000 t of core sheet annually for large and traction transformers. The raw material for the transformer cores arrives in rolls pre-cut to the required width. Then a punching machine punches the metal to size according to the two-limb core design. In the next step, the limbs and yokes are automatically combined into a complete core stack.

Core production

After the core sheets are stacked, the core stack is banded before the coil is attached.

Winding the coil

The transformer plant produces only cylindrical winding, either as layer-layer winding or as layer-coil winding depending on the project requirements. We process approx. 3,500 t of copper annually for large and traction transformers. We use different shapes of conductors, such as circular, flat and transposed conductors. We use Nomex, insuldur and insulating paper as insulation materials.

Pressing and drying the coil

Since the coil tries to return to its natural shape after production due to its elasticity, it must be cold pressed, hot pressed or neither depending on the design. This is necessary to maintain the winding height during assembly. If hot pressing is necessary, the coils are also dried in a circulating air oven.

Active part

After the yoke is put into place, our team of experts mounts the upper clamping frame and the tension rods for clamping the winding. This completes production of the active part. The outbound winding conductors are connected to the bushings with the core in the horizontal position. Normally this takes place by applying the crimping technique. The connections are hard soldered only in exceptions.

Installing the active part

After the active part has been dried and the tank has been prepared (e.g., attachment of pumps, bushings and monitoring equipment), we "marry" the two components. This means that the team inserts the active part into the tank and connects them both mechanically and electrically. Additional components such as resonant-circuit chokes are mounted to the transformer tank. This process step is completed by sealing the tank with a screwed lid.

Evacuation and filling

The transformers are filled with the specified insulating liquid under vacuum. This ensures the quality of the filling process. Depending on the requirements, we use the following media for this purpose: inhibited mineral oil, silicone liquid and ester, categorized in water hazard class 0 – biodegradable. After observance of a socalled settling time, the transformers are ready for the routine and type testing according to IEC 60310.


Testing takes place in a special test bay which consists of a special testing station and two routine testing stations. We are able to conduct all routine testing here. We can also conduct special tests, such as noise and EMC measurements, thanks to the available measuring equipment. We carry out the temperature-rise test as part of the type testing in the test bay for large transformers. After successful testing, the transformers are ready for shipping around the world – and join the approx. 3,500 vehicle transformers that we have successfully manufactured to this day at the transformer plant in Nuremberg in approx. 40 different designs.