Electrical Industry 


When it comes to energy supply in China, you have to think big. More than one billion people in China need electricity. To ensure this supply, a world-record power line, which runs right across the country, goes into operation in 2019. The largest high-voltage direct current (HVDC) transmission line project in the world uses Durostone® EPX-M shield rings from Röchling.

If you take a look at a map, you can already sense, based on the length of the route, how much technical expertise is required for the success of the project. Starting in 2019, power will be transported 3,284 km across the country, in China. The power will be produced in Changji in the northwest and transported by the most powerful HVDC line in the world, far into the east to Guquan. With a transmission capacity of twelve gigawatts, this link reaches a completely new level. By way of comparison, a modern nuclear power plant has an output of between one and two gigawatts.

Latest Generation of Transformers
A leading manufacturer of transformers has developed the latest generation of HVDC transformers for the project – the first ±1,100 kV transformers in the world. With an output of 587.1 megavolt amperes (MVA), they are the most powerful in the world.

Part of the new transformers are shield rings made of Durostone® EPX-M from Röchling in Haren. With these shield rings, in 2014, Röchling was the first manufacturer to release onto the market, shield rings made of glass fiber reinforced material based on synthetic resin, engineered especially for the HVDC technology. Compared with conventional materials such as pressboard or laminated densified wood, the rings show no shrinkage after the vapor-phase drying process. That is an important advantage for the manufacturers of transformers. As Rainer Sanders, General Manager Sales Composites, explains: “Shield rings made of Durostone® EPX-M have very high dimensional stability. Unlike with classic materials, design engineers do not have to take shrinkage into consideration. This makes planning and development easier because manufacturers can perform the calculations using reliable values. Durostone® EPX-M allows for the dimensioning of the transformers with exact tolerances.”

Special Winding Process
Thanks to this advantage, Durostone® EPX-M is used in transformers worldwide. “The market has quickly recognized the advantages of our innovative Durostone® EPX-M. We are pleased that our product has impressed manufacturers of high-capacity transformers around the world and that we are now part of this unique HVDC project in China,” says Sanders.

The rings are manufactured in a special winding process and consist of glass fiber reinforcement and a resin matrix based on epoxy resin. Thanks to a thermal class of H (180°C), Durostone® EPX-M boasts excellent compressive strength even at higher temperatures.

Extensive Range
Rings made of Durostone® EPX-M are part of the extensive range of construction and insulation components from Röchling for use in oil-filled transformers. For more than a century, the plastics processor has been producing the high-performance material Lignostone® Transformerwood® and manufacturing sheets and machined parts such as shield end rings, shield rings, thrust rings, pressure beams and fasteners. With Trafoboard®, since 2010, Röchling has offered insulation material made of high-quality pressboard in accordance with the highest requirements for electrical properties.

High Electrical Outputs, Great Distances
Thanks to their excellent electrical properties, Röchling plastics are used in HVDC projects worldwide, including North-East Agra in India, Rio Madeira in Brazil and NorNed in the Netherlands and Norway. The HVDC transmission is used to transmit high electrical outputs over long distances. With HVDC technology, the three-phase current generated in the power plant is converted to a direct current inside a converter station and then back into a three-phase current at the other end of the line. Compared to transmission of a three-phase current, the loss of power is significantly lower with direct current transmission.


Rainer Sanders
Röchling Industrial
General Manager Sales Composites
Phone: +49 5934 701-332

Photos © kalafoto – Adobe Stock, Röchling