© ESO/L. Calçada

FanGrid for the Extremely Large Tele­scope: Cool view into outer space

Life outside our solar system. The first galaxies. The unex­plored, dark side of the universe. New find­ings about the evolu­tion of every­thing could soon come to light in 2028 when the Extremely Large Tele­scope posi­tioned in Chile, begins directing its 39-meter mirror into space. The laser systems, which are cooled by highly special­ized air handling units from OCRAM CLIMA, play a deci­sive role here. The air handling units are equipped with 28 FanGrid units from ebm-papst.


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 total of 28 FanGrid are installed in the highly special­ized air handling units supplied by OCRAM to the ELT. (Photo | ebm-papst)
All RadiPac come with active PFC and auto­matic reso­nance detec­tion as stan­dard. (Photo | ebm-papst)

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.”

Building the ELT at an alti­tude of 3,000 meters and in the desert poses a number of chal­lenges.

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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