Radio Frequency Interference

For those who are interested in Variable Speed Pumps, I thought this might be something worth reading.

I am an Amateur Radio Operator and frequent this Forum. I had forgotten about this thread until I got a notice that some had resurrected it. The information is pretty interesting about Variable Frequency Drives and the interference they can cause. Among other things.

Eham Forum

bob...

Very interesting thread. Here is another along the same lines. This thread gets very technical but, the point is that there is not really anyway to solve the Radio Frequency Interference problem. The more pumps, furnace blowers, washing machines, etc, equipped with variable speed or frequency drives, the worse the problem becomes. I remember seeing a report years ago about the effects of RFI from florescent lighting causing high stress levels and other physiological problems for humans. Variable Speed or Variable Frequency Drives put out a lot more RFI than florescent lighting.

http://www.eng-tips.com/viewthread.cfm?qid=203504&page=1

I read the thread, and the common conclusion is that the problem VFD's weren't installed to the MFG specifications, as with any new technology, you need to re-train the installers. VFD's are here to stay.

Rancher

VFD's are not new technology. They are at least 30 years old. They have developed new band aids but, they still have not solved the problems. If you read the thread carefully, you will see that these professionals say that no matter how you ground or filter a VFD, or even if you use of all steel conduit, that you can only reduce the RFI, not eliminate it. Manufacturers of VFD's are not being truthful about the noise levels, and they are also lying about being able to save energy. They want you to believe that there really are 20% to 50% energy savings with VFD's. If you believe that, then all the problems and headaches associated with VFD controls, which RFI is just one of, should be worth all the trouble.

A long known theory called Ockam's Razor, http://en.wikipedia.org/wiki/Ockam's_Razor
teaches that when there are two or more ways to accomplish a task, that the simplest way is usually the best way. This theory is also better known as the KISS principle, which stands for Keep It Simple Stupid.

Of course most engineers had rather do just the opposite of this rule. While they still want to accomplish the task at hand, they want it to be so complicated a method that only the engineer can understand it. This normally turns out to be the most expensive method as well. Making more money for the manufacturer, creates job security for the engineer, at the expense of the end user.

Machine tools, conveyor belts, positive displacement pumps, and other applications are all good places to use a VFD. When pumping water at a constant head, which is what well pumps and booster pumps do, VFD's are much more trouble and expense than they are worth. VFD's may be here to stay but, we need to be educated enough to know when, and when they are not needed.

The best way to eliminate RFI, resonance frequency vibration, bearing currents, voltage spikes, and the many other side effects of VFD control, is to not use the VFD to start with. If there were not a better way to control pumps, I would still be using VFD's myself. However, the CSV was designed to replace the VFD, and does an excellent job of it. Since the CSV is newer technology than VFD, and can do a better job with less complications and expense, anyone still using VFD on regular pumps, is just behind on the learning curve.