HOW TO PROTECT DRIVES AT HIGH ALTITUDES
When installing AC drives, most of us give a lot of thought to temperature but how many of us think about altitude?
Barometric pressure decreases as we get further away from the surface of the earth. As the atmosphere becomes thinner, the number of molecules present in the air we breath falls. For us mammals, this means we have to work harder to breath enough oxygen. The lack of oxygen available in our lungs results in a reduced level of oxygen in the blood stream. Known as hypoxia, this is the cause of physiological changes and medical problems which occur at high altitude.
Of the planet's 7.53 billion humans, around 140 million live at an altitude of over 2500 meters. So, most of us don't need to think about the effects of altitude.
Yet, if you are a sea level dweller, you only need to take a trip to a ski resort, or a hike in the mountains to feel the effects of altitude. Normal tasks, for which most of us don't give a second thought, like walking short distances can become very difficult.
How does altitude affect AC drive installation?
What has all this got to do with AC Drives installation? Just as the human body requires a favourable density of oxygen molecules to support respiration. Your AC drives also requires enough air pressure to operate effectively.
One of the first major challenges we face when installing AC Drives at altitude is the ability to remove heat from the system. At high altitude the air's cooling capacity reduces as the number of molecules falls. Without an adequate density of molecules in the air, the potential to transfer heat falls.
When installing an AC Drive, the only way to compensate for this is to decrease the output current of your AC drive. Another option would be to decrease the temperature to the point when 100% output is available.
Although it also worth remembering the obvious temperature benefit of high altitude installations. The higher we climb the ambient temperature tends to fall. On average, the temperature decreases by about 6.5°C/11.7°F for every 1000 m/3281 ft increase in altitude. The necessity to provide effective cooling may lose some of it's urgency at such low temperatures.
Nonetheless, high altitude doesn't always guarantee cold weather. So it is always worth checking the average local temperatures for your installation location. Of course, we must also consider the other effects which can come with cold weather installation. Snow and ice can also effect the operation of your AC Drive, so must also be considered.
How about indoor installation at high altitude?
Of course, indoor installations won't always benefit from cool temperatures. So, this is when you'll need to consider other methods to increase cooling capacity.
The first option would be to increase the amount of air flow over the cooling fins on the AC drive.
The second option would be to use air conditioning to cool the enclosure and account for the effects of thin air.
The last option would be to use a back-channel cooling option. This would bring in cool outdoor air through the back cooling channel and negate the need for expensive air conditioning systems.
When none of these solutions work. Danfoss have a solution which takes away the reliance on air cooling. The Danfoss VACON® NXP Liquid uses a water or water/glycol solution to remove heat from the AC drive. Without air, the system will never really be affected by the changes in air density.
How does altitude affect AC Drives?
When operating at low voltages arcing doesn't generally occur at high altitude. Domestic electrical products can function well. When operating a laptop or a smartphone you shouldn't notice any difference in function, that's despite the lack of space between the copper traces on their circuit boards.
However, when voltage is increased to that of an AC drive, the potential for electrical arcing increases. At an input level of 690 VAC three phase the voltage level on the DC bus is expected to be around 930 VDC. This could be high enough to impact the isolation of low voltage circuits such as communications and I/O. This interference could affect reliability and the safety of the system.
This is why many manufacturers will specify the maximum operating altitude for the drive. If you need help with this, your Northern Industrial adviser will be able to help. The team at Northern Industrial has dealt with installations all over the world, in a huge variety of environments. So we are sure to be able to get you the installation advice you need.
Most drives require derating to start at 1000 m/3281 ft. As an official Danfoss distributor we have a expert knowledge of their products. So we know the general rule is a reduction of 1% of the output current from the AC drive for every 100 m/328 ft above 1000 m/3281 ft. Their maximum allowable altitude is typically 2000 m/6562 ft or 3000 m/9843 ft. However, this rule may not be typical for every manufacturer. Just contact us if you are unsure, our team of expert engineers are sure to be able to help!