Anyone who has ever been bandaged up due to a sports injury knows how important it is to have an even and flat winding. The same applies to the core of a large transformer, which can weigh several hundred tons. Although the automated process is significantly faster, it is also much more difficult than manual winding. Kohls uses gas springs from ACE to ensure optimum winding results. The company has over two decades of experience in the construction of special machines for transformers. The family-run company from Freigericht near Hanau has been able to gradually expand its expertise, particularly in the areas of laying technology for stacks and cores as well as the taping of cores. Managing Director and founder Rüdiger Kohls relies on solutions from a single source, from the creation of initial proposals using 3D software through to assembly and commissioning. This is why the Hessian specialists in transformer construction also attach great importance to long-term relationships with their suppliers, including ACE.

Complex taping process
Taping an industrial transformer, which is often the size of a bungalow, is a complex job where everything has to fit. After all, the thin sheets of the transformer must not move a millimeter when they are erected vertically. This is ensured by special tensioning straps, whose job it is to enable a smooth journey to the taping machine. The safe transportation of the construction, which is fragile at this stage, takes place on an air cushion vehicle, also specially developed by Kohls. Once the transformer components have arrived at the taping machine, it wraps the core with a resin tape consisting of glass fibers impregnated with special resin. The resulting layers gradually increase the tension on the individual transformer legs, which can be up to 250 decanewtons per revolution; one decanewton corresponds to a mass of 1.02 kilograms. Transformers of this type usually operate in an oil bath. Thanks to the bandage using the special machine from Kohls, the transformer ultimately operates more quietly, works more efficiently and ensures more reliable cooling, meaning that expensive material can be saved with the appropriate design. A noteworthy feature of the new machine is Kohls' patent-pending braking system, which generates the aforementioned massive belt tension and converts the braking energy via the hydraulic circuit.

Detail of the Kohls rewinding system with the industrial gas spring, which always maintains the belt tension. © Steffen Bonn, ACE

Industrial gas springs against voltage drop
Especially with oval transformer legs, a voltage drop can occur at some points of the oval. Industrial gas springs from ACE are used here to prevent the voltage drop. Kohls also wanted to make the machine low-vibration. For taping, a toothed ring, on which the brake unit is mounted with a stroke of 150 millimetres, rotates up and down around the transformer leg. ACE recommended the GS19-150-EE-550N industrial gas springs as a solution. These machine elements usually ensure the safe opening and closing of hoods and lids by supporting the operator's manual force. In this case, the industrial gas spring is responsible for ensuring that the belt tension is maintained, as the stroke path still serves as a reserve in the event of interruptions due to almost right-angled cross-sections, for example. The functional principle of the gas springs is identical to the standard case of opening and closing flaps, for which they were originally designed. In this case, hydraulic oil is also used for end position damping in the extension direction.

When the gas springs are activated, for example when a flap is closed, the nitrogen flows through the throttle opening in the piston. The forces act against the weight of the flap and thus regulate its speed. When the flap is opened, the nitrogen flows back, supporting the operator's manual force and enabling a defined extension speed. The oil filling also ensures a gentle touchdown when the flap is extended to its end position. The retraction and extension speed is in turn determined by the throttle opening.

The model used at Kohls has an extension force of 550 newtons, which can be individually adjusted. The modern machine elements are equipped with a valve as standard and can therefore generate the desired pressure. If necessary, ACE can also supply a special nitrogen filling case, which the customer can customize on site. pb

Calculate and design gas springs
On the ace-ace.de website under the menu item 'Calculations', interested parties can calculate, design and order the gas spring tailored to their application. The most common applications for gas springs can be calculated in just a few steps. The optimum ACE gas spring and the required mounting accessories are specified exactly. It is possible to visualize the gas spring application either in 2D or 3D.