28.09.2020 | Innovative asset management at Axpo
In a pilot project within the framework of the Grid 4.0 programme, Axpo manufactured a connection clamp for a 50-kV transmission line in an additive process. It matches the original both mechanically and electrically. This technology enables spare parts to be manufactured quickly and when needed. A pioneering step into the future?
Axpo's supra-regional transmission grid on the 50- and 110-kV level comprises 2200 km of transmission lines and 50 substations. It is operated based on the n-1-principle: When a grid element malfunctions, redundant lines transmit the power.
However, the grid is then unprotected against other malfunctions – sometimes an entire region is supplied by just a single element. If this component were to fail as well, it would result in a regional power outage. Hence, the defective element must be repaired or replaced as quickly as possible.
Albert Raymann is in charge of several of Axpo's substations, including the Grynau substation near Uznach: "Our installations are often 30 or 40 years old. If we don't have the part in stock, it can often be difficult to order it from the manufacturers." Delivery times of several weeks to months are not unusual, for example, if the manufacturer has to reproduce a casting.
In addition, Axpo has been using a connection bolt with an uncommon diameter of 35 millimetres in its substations for historical reasons. Transmission lines are connected to these bolts with clamps. The output terminals have to be especially manufactured by Axpo. "If we can't procure the spare part on short notice, we have to improvise," says Raymann. "Up to now we have always found a solution, but, of course, this is not an optimal situation."
Whether spares can be additively produced – innovatively with a 3D metal printer – is being tested in a pilot project. In addition to Raymann, who is responsible for the project on the operative side, Timo Stiefel joined in as a project engineer for primary technology in order to look at the material aspects more closely.
Output terminals were cast from bronze in the past. Today, an aluminium-based alloy with AlSiMg is commonly used. It is lighter than bronze. The aluminium alloy AlSi10Mg is suitable for castings as well as for additive processes such as laser sintering. In this process, the part is manufactured in a powder bed: A laser melts the metal powder at the point where the part will grow. Powder is added layer by layer and selectively melted with the laser.
Axpo does not have its own additive fabrication facility. The project team turned to Adriaan Spierings from Inspire, a research company in the area of production technologies that is specialised in transferring know-how from the ETH to industry. The company has a great deal of experience in additive fabrication.
Inspire first made a 3D scan of the replacement clamp that would be tested under the pilot project at the
Grynau substation. The original clamp was designed for a transmission line with a diameter of 17.5 mm. Since the clamp in the substation would be used for a line with a 26-mm diameter, Inspire adapted the CAD data for the clamp to the larger diameter after the scan. Other geometrical modifications were also carried out in order to better meet the requirements of the 3D printer. The part also required support elements that would be removed after 3D printing.
The additive process is often used to manufacture delicate, complicated parts. In contrast, the clamp produced in the pilot project is a massive metal part. At first glance, there does not appear to be an advantage in manufacturing a replacement clamp in an additive process. But when a single part is needed quickly, for example in substation maintenance, additive fabrication has a big advantage: The spare part is available in just a few days.
The actual 3D printing process takes two days. The manufacture of the clamp takes about one work week including data preparation and post-production work (removing the supporting elements, drilling holes and thread cutting). With the current technology a spare part can be fabricated and installed within a week of the malfunction occurrence.
Before the part was installed at the Grynau substation, the University of Applied Sciences (NTB) in Buchs tested the conductivity of the additive manufactured aluminium. The result was satisfactory and the material samples exhibited values comparable to those of conventionally manufactured – cast – clamps.
After the tests, the clamp was connected to the 50-kV double line running from the Grynau substation to Niederurnen. The pilot project was carried out without any time pressure and the clamp was tested on a line that had no impact on the grid. The installation was problem-free. The contact resistance measurement on the installed clamp produced values comparable to conventionally manufactured clamps.
The pilot project confirms that it is possible to manufacture grid elements with a 3D printer. What are Axpo's conclusions? Jörg Kottmann, Head of Asset Management: "The pilot project proved that it works. We now want to collect the 3D data for critical operating parts like clamps – especially those components for which no spares are available. This will enable us to act more quickly when needed."
However, the technology is currently too expensive to be used on a broad basis, for example to reduce inventory costs. But the technology will continue to develop. Axpo plans to request the 3D data for equipment that will be procured in the future and to file it in a structured form.