It’s a harsh world… part 4 – Drives vs High temperatures

Tuesday, April 5, 2016
Industrial metal forge

38°C / 100°F – that’s the maximum daily temperature we had last summer here in Madrid for 24 consecutive days! However, that’s nothing compared to desert areas, where temperatures can – and do – exceed 50°C / 122°F. Even in less extreme climates, AC drives can be exposed to high temperatures. For example, they can be installed in cabinets or rooms not properly ventilated or air conditioned, or close to a heat source, as can often be found in the metals industry.

Given the Scandinavian heritage of Danfoss Drives, you might think that our AC-drives portfolio is far better suited to the very cold environments we discussed last week. Being a global player, and encountering practically every application in a wide variety of environments, though, has allowed us to prove to our customers time and time again that nothing could be further from the truth. So, this time around, we’ll provide some guidance to make sure your AC drives survive in these extreme conditions.

Starting with specifications tables, you’ll notice that every AC-drive model lists both an operating temperature and a storage temperature. You may not be aware of what kind of an impact storage temperature has on your AC drive. But, if the storage temperature is exceeded, for example if your AC drive is stored in direct sunlight, the capacitors could be damaged. Electrolytic capacitors, which are the most common capacitor types found in AC drives today, are especially susceptible to high temperatures in storage. These high temperatures result in elevated internal pressures in the capacitors and accelerate the natural aging processes that occurs as the electrolyte dries out over time. However, if your AC drive relies on thin film capacitors, that can be found, for example, in the VACON® 100 INDUSTRIAL and the VACON® 100 FLOW, your drive will be less likely to fail due to extended storage times or high storage temperatures.

Reliable operation at full load

What you’re probably more concerned with, and for a good reason, is how your AC drive operates at or near the specified maximum ambient temperature while at full load. If this operating temperature, which is most often 40°C / 104°F but may be higher depending on the AC drive being used, is exceeded or not properly accounted for, it can lead to premature failure of your AC drive. Long-term exposure to high operating temperatures also reduces the lifetime of the electronics. A good rule of thumb is a reduction in lifetime of around 50% for each 10°C / 18°F that it is operated above the component’s rated maximum operating temperature. Because of this, if you expect to run into higher ambient temperature operating conditions, it’s important to select an AC drive that is designed to work properly at your expected maximum temperature.

Part of how AC drives extend the maximum operating temperature range upwards is by using a built-in derating algorithm to adjust and limit the output current to the motor as the temperature increases. As you can imagine, this is also a function that protects both the drive and the motor from being damaged by operating at higher temperatures. Due to this, if you have a particularly tough application operating near these maximum ambient temperatures, it may make sense to increase the drive rating to ensure proper operation. The need to derate an AC drive is not only influenced by temperature; it is also influenced by the switching pattern and switching frequency selected for the insulated-gate bipolar transistors (IGBTs). Higher switching frequency values result in higher losses for the same ambient operating temperatures, so some AC-drive models will limit the switching frequency as the temperatures climb. Other factors, such as load cycles for example, can also affect how your AC drive functions at high temperatures.

Choosing the right drive for your application

This is, potentially, a tough call. To assist in this selection, the Danfoss Drives portfolio features a wide selection of AC drives that can operate at full load without derating up to 50°C / 122°F. With some AC drives, such as the VLT® AQUA Drive and the VLT® AutomationDrive, in certain frame sizes and enclosure classifications, it’s also possible to derate for temperatures up to 55°C / 131°F. When it comes to even higher temperature operation, AC-drive selections become more limited. Up to 60°C / 140°F, the VACON® 100 X with derating is a well-suited option to use as it combines large front cooling fins and oversized cooling fans.

Some applications will, perhaps surprisingly, require AC drives that are regularly exposed to temperatures as high as 70°C / 158°F! For these even more demanding operating conditions, Danfoss Drives has an ace up its sleeve: the VACON® 20 Cold Plate. This AC drive – or more accurately, AC-drive module – consists of a flat surface onto which the majority of the heat losses are concentrated. By attaching this surface to a cooling element, such as a heat sink with large cooling ribs or a liquid-cooled heat exchanger, the VACON® 20 Cold Plate can reliably operate at these excessive temperatures.

Think about where you’re installing the drive

Simply selecting the AC drive with the right operating temperature rating, though, isn’t the complete story. Sometimes your application may be so demanding that there doesn’t appear to be an option that fits all of your needs. In these cases, you will have to actively fight to keep the ambient temperatures down to acceptable levels. The method and location of installation of your AC drive play a big part in the methods that can be used to keep ambient temperatures under control. For drives located in an electrical room or mounted in a cabinet indoors, a typical solution is using air conditioning which also keeps the room or cabinet dry. In large installations, though, this can become a costly solution – especially if the only devices being cooled are the AC drives.

To help minimize installation costs for air-cooled AC-drive installations, a back-channel cooling solution – sometimes referred to as flange mounting – can be utilized. This results in the majority of the heat being directed outside of the enclosure or room which reduces both the footprint and cooling requirements. This solution keeps most of the control electronics housed within the panel, while the heatsink protrudes through the panel where it can be cooled with external air flow, or by a separate air duct. When your application has high power requirements where larger frame sizes or many drives are installed in one place, the benefits of this installation method can be easily seen; efficiency and process improvements are combined with a reduction in energy and maintenance costs.

Let’s talk about liquid cooling

Sometimes, though, due to space requirements, higher altitude operation, or exceedingly high ambient temperatures, air cooling just doesn’t cut it. When it comes to these situations, you’re in luck! The VACON® NXP Liquid Cooled series offers some impressive power density because liquid cooling is far more efficient in transferring heat than air cooling. As a matter of fact, these AC drives dissipate less than 5% of the heat losses via air. As a result, an additional benefit of liquid-cooled AC drives is that there’s no need to build a separate room, further reducing installation costs. And because there are, at most, small circulation fans on the VACON® NXP Liquid Cooled drive modules, it also means that the AC drives are practically whisper quiet.

Of course, not all AC drives are located inside. So, for those of you who have AC drives located outside, don’t forget that IP66, UL Type 3R and UL Type 4X enclosures, even if they are outdoor rated, have a maximum operating temperature. If your AC drive is in direct sunlight, that will also raise the temperature of the drive and definitely can have an impact on its operation. It’s best to make sure that if you can’t find a nice place in the shade for your AC drive, that you at least provide it with something to block the sun’s rays.

As you can see, even a topic as seemingly clear-cut as high temperatures has its unique challenges. Making smart, informed decisions will help ensure that your investment operates worry-free for several years. We here at Danfoss Drives have worked on installations in some of the hottest environments in the world. So you can count on us to help make sure you have the optimal solution for your application.

Abraham González Ponce, Application Knowledge Manager, Application & Service Products, Danfoss Drives
Jake Roeder, Global Product Marketing Manager, Danfoss Drives