With more than 300 cloudless nights each year under a clear, star-filled sky, cold, dry air, and no light pollution from sources such as cities for more than 100 kilometers, the Cerro Armazones mountain, at an altitude of just under 3,000 meters, is the perfect location for the Extremely Large Telescope (ELT). Despite these advantages, the Atacama Desert also harbors major challenges. The fine desert sand and dust is dangerous for the telescope’s technology. Temperatures can vary wildly between day and night. Moreover, Chile is one of the most seismically active regions in the world, which means that the ELT must stand firm on the sometimes unstable terrain.
Protection is therefore the key issue when it comes to the world’s largest telescope. Around the clock, countless components and systems will ensure the optimum operation of the observatory, which is estimated to cost € 1.45 billion. In order to look so far into space and receive clear images, the optical instruments are extremely sensitive. Even the slightest air turbulence in the dome of the telescope could distort measurements. Therefore, one of the safety measures involves adjusting the temperature inside the dome to match the outside temperature over several hours before opening the large dome doors.
The Extremely Large Telescope is currently being built on the Cerro Armazones mountain. It will be operated by the European Space Observatory ESO and completion is expected in 2028.
The ELT has the largest optical mirror in the world, consisting of 789 individual mirrors. The guide star laser systems ensure sharp images.
AHUs for the guide star laser systems
When the dome is open, a spectacular show begins. The laser systems direct their beams into the night sky to create as many as eight artificial guide stars that will be used by the adaptive optics system to measure atmospheric turbulence and make the necessary corrections. The images produced by the ELT will be 16 times sharper than those from the Hubble Space Telescope – even though the Hubble explores space from space itself. “Everything is different. And there is no leeway for error,” is how Marco Lopes, CEO of Ocram, summarizes the project. For 25 years, the Portuguese company has specialized in customized air handling units (AHUs) for customers’ demanding applications – like the ELT in Chile.
46
AHUs are cooling the laser systems
28
FanGrid units from ebm-papst are built in
168
RadiPac EC fans in total
Behind the scenes, a total of 46 AHUs designed by Ocram will supply a constant stream of pure air conditioned to the perfect temperature to cool the laser systems – invisible but critical, because even a small fluctuation in temperature or minuscule contamination (such as a dust particle) could jeopardize the work of the ELT researchers.
For this reason, the demands placed on the ventilation systems and their components – such as the fans – are very complex and exacting. First, there is the location. Even at an altitude of 3,000 meters, the units have to operate reliably to ensure the right output and necessary pressure. Their function must not be impaired by earthquakes or desert sand blocking the filters. “Logistics is also a critical aspect because the construction site is hundreds of kilometers into the desert. We are planning to ship 70 containers to Chile,” says Marco Lopes. Second, there is the ELT itself. The systems will operate in an extreme environment and consist of incredibly sensitive electronics and sensors. Under no circumstances may they cause any interference.
A highly specialized plug-&-play solution
Validations, simulations, pages of tables with calculations, stakeholders in different countries: Designing high-end AHUs for such an unusual project is extremely complex, as was creating the initial fan solution. “The fans had a few additional components. For example, the capacitors were to be located externally, which would have caused us more work with the cabling. And every additional component in the system means more risk and another challenge for us,” explains Marco Lopes. “We wanted a solution that would make our job easier, so we contacted ebm-papst in Portugal.”
Ocram outlined the conditions of the order. First, there were the aforementioned technical specifications – earthquake-proof, high-altitude functionality, absolute reliability – coupled with fixed delivery times and maximum economy. “Not a project you get offered every day,” says Nuno Pires, Managing Director of ebm-papst Portugal. “However, it’s one where we can deploy our entire engineering capability. That’s why we took on the challenge.”
First of all, a small and flexible ebm-papst team was established with support from Mulfingen. The engineers, technicians and production employees had the task of resolving the complexity of the Ocram system. “Instead of giving our customer a set of building blocks to assemble themselves, they will receive a finished plug-and-play product. “A solution equipped with all the necessary components and requiring no additional installation effort,” says Nuno Pires.
Together with ebm-papst, we are working on a project that goes far beyond planet Earth.
Marco Lopes, CEO OCRAM CLMA
Active PFC und automatic resonance detection
The solution included, for example, integrating the aforementioned capacitors into the fan. And to protect the ELT’s technical instruments, all the fans are equipped with active PFC as standard. “The limit values for current harmonics were strict – a maximum of ten percent. Our simulations show we are significantly below this at a maximum of five.” To ensure the system’s performance and operational reliability, the team proposed a FanGrid consisting of six EC fans. If one fan fails, the remaining five can still deliver the necessary output. “We have also equipped them with other devices to protect against possible resonance or seismic activity,” says Nuno Pires. There will be a total of 28 such FanGrid units. “ebm-papst has done an excellent job. Because the solution was so impressive, we switched from the original large AC fans to several small EC fans,” says Marco Lopes.
Integrated active power-factor correction (PFC)
Due to their circuitry, EC fans have a pulsed current draw as opposed to sinusoidal. This deviation causes current harmonics, which lead to a so-called distortion reactive power that puts strain on the supply network. If even the slightest distortion is problematic due to the application, the harmonic content in the current must be reduced to a minimum. ebm-papst is the first fan manufacturer to integrate a three-phase, active PFC stage in the form of an active rectifier in its EC fans. The pulsed input current of the EC motors is converted into a sinusoidal input current without additional effort for the user and minimizes circuit feedback.
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