12/10/2019

Professional article: How your motor keeps a cool head

Cover picture Thermography

Production is running at full speed. If the production lines continue to work this way, it will set a new monthly record. The production manager can proudly inform the managing director, who can achieve the desired quarterly result. But suddenly: a standstill in the production line. Cause: the drive in the packaging system is overheated and it must be replaced.

You can avoid this "horror scenario". Imagine the entire chain, from the generation of heat in the electric drive to the ambient air into which all the heat energy passes at the end. Every single step should be considered and, if necessary, improved.

Let's start with the three main heat sources:

  • Electrical resistance: current flows through the copper windings of a motor, solder joints and electronic components. Depending on the motor current, circuit design and quality of the components, more or less electrical energy is converted into heat.
  • Eddy currents / remagnetization losses: electrical energy and rotational energy are converted into heat energy by constantly remagnetizing the motor sheet used or by eddy currents.
  • Friction losses: rolling ball bearings and gears and lubricants that are moved convert kinetic energy and thermal energy.

Your objection could now be that you as a user can hardly change the heat sources. After all, you have no influence on the gear materials used, the iron sheets or the electrical components used by the manufacturer. But it is precisely here at the heat source that you have many possibilities to control that as much heat as possible is generated that would otherwise have to be dissipated later at great expense:

Choose a motor with high efficiency and operate the motor at the point with the highest efficiency. The manufacturer will provide you with the relevant information. Motors operated with vector control have a particularly high degree of efficiency.

  • Do not compare apples with pears. Only if the specification values were recorded without an additional cooling plate (according to EN 60034) are they representative and comparable. Care must also be taken with gearboxes. Does the manufacturer specify the overall efficiency or only the theoretical gear efficiency? A 97 % gear efficiency can quickly turn into an 80 % overall efficiency and thus the gear unit into a strong heat source.
  • If in doubt, test your drive in the application under worst-case conditions. Smart motors have integrated temperature sensors whose values you can read out.
  • Depending on the application, special high-temperature greases can be used in gearboxes so that they generate less heat loss.

Of course, the generation of heat cannot be completely avoided. This heat must now be released into the ambient air. Now you could spontaneously say: if the drive becomes too warm, I use a fan. Due to noise, costs and limited fan life, forced ventilation should only be an option if all other options fail. But there are plenty of options.

To illustrate the heat flow from the drive to the ambient air, you can compare the heat with water. This water falls as continuous rain (constant supply of heat energy) to the sea (ambient air). If the water has to pass through almost impenetrable rock, it accumulates and flows off slowly. If, instead, it flows through a wide riverbed, there is no waterlogging and it flows off unhindered.

The impenetrable rock in this comparison are substances with poor thermal conductivity. High-alloy steel conducts heat up to 10 times worse than aluminium alloys. These alloys conduct heat up to 1,000 times better than many engineering plastics and almost 10,000 times better than air. In this comparison, the wide river bed is a material with good thermal conductivity and a large cross-section.

In order to allow the heat to flow off well, make sure that the drive is attached to a large area of heat-conducting material. Even an air gap 100 μm wide would dissipate the heat as poorly as over a distance of approx. 1000 mm aluminium. Good thermal bonding distributes the heat well in the application and has a large surface from which the heat is released into the ambient air.
Avoid closed housings. Wherever possible, provide large ventilation slots in the machine or device. By natural convection, ambient air is sucked in at the bottom of the housing in which the air absorbs the heat loss of the components and it is emitted heated at the top. This, of course, only applies if there are ventilation slots with a correspondingly large cross-section.

Use decentralized drive technology with integrated electronics. The heat loss of the motor electronics is thus generated in a decentralized manner and distributed in machines and not concentrated in a control cabinet. Compare it to continuous rain: if a large amount of water rains on a spot, it drains off much more slowly than if it were distributed over many areas.

If you take all these points into account, your drive will keep a cool head. But what if the drives are unexpectedly overloaded, for example due to wear in the machine or incorrect operation? The drive must be prepared for these cases. Modern smart motors and drives work with algorithms that not only take the motor temperature into account, but also calculate in advance, based on the current load, how long the motor may still run until it overheats, limiting the output power beforehand.

You should therefore also check the status information, that can be read out cyclically via the bus interface of the motor. If the temperature or currents change significantly compared to the previous cycles, these can be an indicator of pending defects.
Dunkermotoren has been building fully integrated smart motors and drives for about 20 years and has extensive experience with sophisticated thermal design. This not only applies to the heat dissipation in the application, it also begins inside the motor. The optimized heat flow in the motor housing ensures that the heat is optimally transported to the housing surface and that the temperature-critical components operate in the non-critical range.

Application consulting for Dunkermotoren helps customers with the thermal design of the drives, so they do not overheat even under extreme conditions. After all, customers do not want to jeopardize the quarterly results, but rather work with reliable drives.



Your contact for Public Relations

Janina Dietsche
Marketing Live Communication & PR

Dunkermotoren GmbH
Allmendstr. 11
79848 Bonndorf, Germany

Phone +49 7703 930 - 546
Fax      +49 7703 930 - 102
Janina.Dietsche-DIESEN TEXT ENTFERNEN-@ametek.com

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