How To Protect VFD From Overheating

 

30 Aug, 2022.

In this post, we will see how to protect VFD from overheating.

VFD means variable frequency drives. It is an electronic equipment through which the speed of the motor can be varied. VFD uses a vast number of power electronics components like triac, diac, MOSFET’s, transistors and a lot more.  Basically, as the VFD is running a motor, it means simply it is handling a load. With the load, comes it’s effects. Motor can many a times run in overload condition. Also, VFD is having a large number of semiconductors which always dissipate heat when running. Both these factors are a major contributor to a common issue in VFD – overheating. Overheating exists in every VFD and it depends on how you are operating the VFD and maintaining it’s environment. If overheating is not controlled after a long tenure of time, then it may damage the VFD overall or either it’s internal components. In this post, we will see the concept of overheating and how to avoid it.

What is Overheating?

As the name implies, overheating is a state in VFD where it’s operating temperature increases to a great extent; resulting in heating up of it’s nearby environment or it’s internal parts. Excessive heat for a prolonged period of time results in damage of components.  

How does Overheating Occur?

1.  If the current supplied by the VFD exceeds the standard ratings, it means the VFD is drawing a large amount of current. This results in excessive heating.

2.  Fans are an essential part of VFD to cool it and remove excess heat from the running VFD. This means that the fans are the parts which run daily and frequently. So, there are vast chances of it getting damaged or failed. If you are not maintaining the fan regularly or replacing it, then the VFD will not be able to control the heat generated and this will result in overheating.

3. Heat sinks are used in VFD to dissipate the heat generated from semiconductors. They draw the heat away into the atmosphere. As dust and other contaminants (plant moisture containing oil and other metallic particles) often accumulate on the heat sink, their efficiency decreases. Because, after a certain period of time, it may get choked up (airflow becomes restricted) and then, there will be no use of heat sinks. So, if heat sink fails, then it may result in overheating.

4. Moisture is also a very critical factor in increasing heat. Moisture causes corrosion in electronic chips and boards; which prevents internal condensation and thus, generates heat.

5.  If you are running a wrong motor for a prolonged period of time (means whose ratings are rarely matching the one with VFD), then it will always result in overcurrent and thus, increase the heat.

6. VFD’s are always packed in an enclosure. If the enclosure is not properly designed to draw the heat away, then it will trap the heat and thus, increase overheating.

7.  Some plant operators mostly run the motor at lower frequencies. If the load is large and then too it is doing the work at slower speeds, that means the VFD is drawing higher currents to generate the necessary torque and accomplish the task. This in turn results the VFD mostly running in large current withdrawal and thus, causing overheating.

How to Protect VFD from Overheating?

1.  Always maintain and regularly check the VFD fans. Clean them properly in shutdown condition; and if you find that the fan is not working, then replace it immediately. You can also compressed air system to clean the fans and heat sinks on a regular basis. If you hear strange sounds from the running fan, then you can identify that the fan is not running properly and needs to be checked.

2. Use temperature probes inside the VFD panels. This will measure the temperature inside the panel and if you find any unnecessary deviation (on the higher side) in it, then take immediate action to see what has gone wrong.

3.  You can use dehumidifiers to remove excess moisture from the panel.

4.  Do not run the motor in an overcurrent situation frequently. Choose the right motor and it’s necessary supporting environment (with correct ratings), so that the VFD always runs the motor in a normal condition. Ensure that you are choosing the correct load ratings for the motor.

5.  Check for damaged components like leaking capacitors, corroded parts on circuit boards or chips on a regular basis.

6. Run the VFD at lower frequencies only when required. Do not run it unnecessarily.

7.  Refer the below image. As discussed earlier, the enclosure which is used to protect a VFD can in turn become a major factor for overheating. So, a properly designed panel enclosure must always a proper path to throw away excess heat. In this point, we are talking about passive cooling. It means natural path of heat transfer is utilized, going from higher temperature source to lower temperature source. Like in the below image, filter fans at the bottom will suck normal ambient air from outside into the enclosure. This air travels from bottom to top, taking the excess heat with it which is generated, to the exhaust fan placed at the top. This fan will throw away the extra heat generated. So, it is also necessary to maintain both these fans for proper operation.

8. Most electrical panels containing a VFD are also installed with air conditioners nowadays. This is called active cooling; because you require an external cooling source medium for dissipating the heat. Similar to a normal AHU where temperature is maintained through refrigeration cycle, the temperature of the VFD panel too is maintained here.

     I have covered the general principles used in protecting a VFD from overheating. I have also not attempted to cover every theory of these types deeply; you can learn it easily once you get familiar with them. I have just given you an insight of these types of controls. Once you are done with these, I am hopeful you will be easily able to understand any VFD system properly. Learn the basics and explore a new type of study in this type of automation. It will take some practice and as you go on studying the VFD, you will become more familiar with it.

            Thank you guys; I hope you enjoyed reading the practices normally               used for this type of study in industrial automation.