Homeowner VFD or CSV

[Cary Austin]

Recently they made everyone send back their Goulds Balance Flow controllers to get a new computer chip installed. So the ones they are selling now have less than a year track record.  Only time will tell if any of these will still be working in five years.  Buy a three phase motor, and decide you don't like the variable speed controller, now you have to buy a new single phase motor. 4.5 gallon tank actually holds about a gallon of water, pump has to come on every time you flush a toilet. The most recent problem I am hearing from installers is that when the sprinkler system comes on, the one gallon in the tank is gone in seconds, the BF controller has a slow start so it takes a while for the sprinklers to start squirting. Mean time the bladder in the tank has bottomed out, pressure is low, pipes start shaking and rattling, lot of noise heard in the house. One installer said he has to strap all the pipes down to the floor or walls just to keep them from breaking.  Other Variable Speed Pumps on the market also react slowly causing the same problem.   Variable frequency controllers send out a radio signal that blocks AM radio, cell phones, and causes static lines on you TV. This radio signal that escapes is called stray voltage. They are just finding out that this stray voltage is causing dairy cattle to get sick and produce 20 to 30% less milk.  A VFD is a computer that controls your pump. How dependable do you think you water supply would be using computerized controls? Use a standard pump, little larger pressure tank (20 gal size holds 5 gallons of water), single phase motor and control, and a Cycle Stop Valve to provide the constant pressure. Simple controls make dependable pump systems. Nothing is more annoying than waking up to no water coming out of the faucet.

The harmonics from a VFD are fed back into the electric grid. If you have a VFD with 6 switch operations, then all harmonics not divisible by 6 (7th, 9th,11th, 13th, etc.) are forced back into the incoming power supply. I am sure the VFD machine itself can broadcast radio frequencies but, the harmonics fed back into the power supply can use the incoming power wires as an antenna. Most insulated electric wire in a house has 600 Volt insulation. A 240 volt VFD produces voltage spikes of up to 1000 volts and a 480 volt drive produces spikes of 2000 volts. Your 600 volt insulated wires can't hold back these 1000 volt spikes and they leak out anywhere they can. Also you would have to use wires that have metal or copper shields properly grounded around them to hold in the radio frequencies. Otherwise any or every wire in or around your home can be transmitting radio frequencies from the VFD. Why else would AM radios stop working when you just get close to the area? Your neighbors VFD could actually be affecting you. I also disagree that the motor will last because it can't tolerate the 1000 volt spikes from the VFD for very long. Not to mention that reducing the speed of the pump/motor causes it to go through the mechanical frequency of every component in the pump/motor. At standard 3450 RPM these mechanical frequencies have been balanced out. But at 3120 RPM the motor shaft vibrates. At 3266 RPM the laminations in the motor vibrate. At 3289 RPM the impeller vibrates and so on. Its really calledresonance but, it is still a vibration.Its like driving a car with one unbalanced tire. Even though the tire is what is unbalanced it shakes the whole car and eventually the car starts falling apart. Then there is the "skin effect". Radio frequencies, which is what the motor runs on when using a VFD, travel on the skin of wire unlike regular AC voltage which travels in the core of the wire. When this radio frequency leaks out of the wiring it then travels on the skin of the equipment such as steel pipe and fittings, pump and motor casings, etc. It causes damage that looks like electrolysis, which is the soft particles in the metal dissolving into the water. Then there is the excess heat buildup in the motor from operating on harmonic frequencies and EDM currents that require motor shafts to be grounded to prevent bearing failure. I could go on with other negative side effects of the VFD. We stopped using VFD's in 1992. We realized back then that anything we did to help solve these problems was just a band aid. The root of these problems can't be fixed unless you can change the laws of nature. We built the Cycle Stop Valve in 1993 to simulate the control of a VFD without causing all the negative side effects of VFD. It turned out to be a very simple thing to do. When we realized that we got the same power reduction by using a valve to control a normal full speed pump as they get when slowing the RPM with a VFD, everything else was just icing on the cake. No matter how they try to tell you that the VFD is the most advanced technology, the Cycle Stop Valve is newer and more advanced because it can do more with less.
http://cyclestopvalves.com/comparisons_13.html
http://cyclestopvalves.com/comparisons_5.html
http://www.cyclestopvalves.com/video/conserving_water-dsl.wmv

[Tom101]

Wire insulation breakdown voltages have nothing to do with anything. If you exceed the insulation breakdown voltage you have really screwed up the design and the system will fail.

There are no 1000V spikes inherent in a VFD. If they were generated by the switching devices (e.g., opening an inductive [motor] load, the electronics must eliminate them or the switching devices would generally fail. This is usually accomplished by a reverse diode across the switching device to dump the resulting energy spike.

VFD motors are designed for variable speed. Motors that are not will probably not suffer from imbalance. There may be other electrical issues, but they are balanced. There may be resonances, but balanced is balanced.

Properly designed systems do not put noise back on the power line. A VFD drive generally first converts line voltage to a DC supply using the same type of switching power supplies mentioned by Bob NH. This power supply effectively decouples the VFD signal from the line. A DC supply meeting current standards also corrects power factor to the line.

Yes a square wave generates all harmonics of the fundamental frequency. No it does not get back to the line in a properly designed system. In a poorly designed system it mostly annoys things like X10 remote controls which operate at very low frequencies. The harmonics may also annoy an AM radio with little line isolation or via radiation for short ranges. As noted, so will a PC or flourescent light. I have some lights I bought from HD and they ruin my FM radio reception. They have lousy line isolation and the tubes radiate. Local radiation is short range and since the wavelength of the frequencies involved in an VFD are very long the equipment is not a very efficient antenna; hence minimal ambient radiation. A switching power supply (which also generates square waves) can have switching frequencies into the megahertz range and are much more likely to be a problem.

I am also not sure why a VFD drive would provide less overall efficiency when matched to the load characteristics than any other possible solution. Certainly not pumping at max capacity and throwing away some large fraction of the energy applied via a bypass back to the source. That is not why VFD drives are very popular industrial solution as a energy saving device. A VFD pump coupled with the appropriate sensor should provide a very effective pumping solution without wasted energy.

I do not believe that the concept of "carrier frequency" applies to a VFD controller.

[Cary Austin]

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VFD systems have so many complications that very few people understand them all. I learned what I know about VFD the hard way. I experienced the problems in the field, then I researched the subject until I figured out what caused the problem. This was pre Internet days and was much harder to get the information needed. These days people can easily search the web for this information. I could explain these things for you but I took the time to find a few links so you could read it in someone else's words. There are many more articles on the web that will give you the real story, not just the white washed version that is in brochures of those who sell VFD's.

"Wire insulation breakdown voltages have nothing to do with anything. If you exceed the insulation breakdown voltage you have really screwed up the design and the system will fail."
"This causes very high turn-to-turn voltages which can produce premature insulation breakdown."

http://www.findarticles.com/p/articles/mi_m0BPR/is_11_17/ai_67339988


"There are no 1000V spikes inherent in a VFD. If they were generated by the switching devices (e.g., opening an inductive [motor] load, the electronics must eliminate them or the switching devices would generally fail. This is usually accomplished by a reverse diode across the switching device to dump the resulting energy spike."
"This creates a severe voltage spike in the source, in this case the output transistors of the VFD, which can immediately cause them to short from dV/dt (too rapid of a rate of change in voltage), or at the very least do incremental damage to the silicon substrate of the transistor. The drive doesn't really "care", but the owner will when the repair and downtime bill comes in."
http://www.usmotors.com/Datasheets/PDF_PDS/pds204-194.pdf

"This motor, as it becomes available, would be the preferred choice for 480V and 575V IGBT drive systems having 2 pu reflected wave motor voltages of 1300 Vpk and 1600 Vpk respectively." See Riding the Reflective Wave at

http://www.ab.com/drives/techpapers/ieee/pcic.pdf


"VFD motors are designed for variable speed. Motors that are not will probably not suffer from imbalance. There may be other electrical issues, but they are balanced. There may be resonances, but balanced is balanced."
You are correct about it being resonance and not balance but the motor does not know the difference because it is still vibrating like crazy. Motors specifically made to work with VFD are standard induction motors that have been modified with 2,000 volt insulation, insulated bearings, shaft grounding capability, etc. to try and offset the destructive parameters of the VFD.
"The motor used in a VFD system is usually a standard squirrel cage three phase induction motor." http://en.wikipedia.org/wiki/Variable_Frequency_Drive

"Properly designed systems do not put noise back on the power line. A VFD drive generally first converts line voltage to a DC supply using the same type of switching power supplies mentioned by Bob NH. This power supply effectively decouples the VFD signal from the line. A DC supply meeting current standards also corrects power factor to the line."
"When these diode blocks conduct power to charge the DC bus of the drive they cause an imbalance in the current waveform that causes an imbalance in the voltage waveform. This imbalance (disturbance) appears at the input of the drive and is reflected into the AC line feeding the drive."

http://www.usmotors.com/Datasheets/PDF_PDS/pds204-194.pdf

"Yes a square wave generates all harmonics of the fundamental frequency. No it does not get back to the line in a properly designed system. In a poorly designed system it mostly annoys things like X10 remote controls which operate at very low frequencies. The harmonics may also annoy an AM radio with little line isolation or via radiation for short ranges. As noted, so will a PC or flourescent light. I have some lights I bought from HD and they ruin my FM radio reception. They have lousy line isolation and the tubes radiate. Local radiation is short range and since the wavelength of the frequencies involved in an VFD are very long the equipment is not a very efficient antenna; hence minimal ambient radiation. A switching power supply (which also generates square waves) can have switching frequencies into the megahertz range and are much more likely to be a problem."
"This imbalance (disturbance) appears at the input of the drive and is reflected into the AC line feeding the drive."

http://www.ab.com/drives/techpapers/ieee/pcic.pdf

"I am also not sure why a VFD drive would provide less overall efficiency when matched to the load characteristics than any other possible solution. Certainly not pumping at max capacity and throwing away some large fraction of the energy applied via a bypass back to the source. That is not why VFD drives are very popular industrial solution as a energy saving device. A VFD pump coupled with the appropriate sensor should provide a very effective pumping solution without wasted energy."
"A VFD does provide efficient control for pumping applications. There is just such little difference in constant pressure systems in using a drive and restricting the flow of a pump with a valve, (not dumping excess flow with a valve) that it never pays back the added expense."
http://www.cyclestopvalves.com/comparisons_13.html

"I do not believe that the concept of "carrier frequency" applies to a VFD controller."
"The switching rate of the output transistors is controlled by the VFD's Carrier Frequency parameter. Increasing the Carrier Frequency will reduce the audible noise from the motor."
http://www.control.com/1026203703/index_html

[Ron Kyger]

It hasn't become an issue for irrigation and domestic pumps yet, but eventually there will be problems with vibration caused by variable speed pumps operating within critical frequencies. I should say, when they have the problem, they don't know what is causing it. All machines have a critical frequency.

In industrial applications, the drives are complicated enough to allow you to actually go in and "lock-out" the critical frequency. As the machine ramps up or down and nears the critical frequency, the drive speeds through it. Lets say that critical frequency is 52Hz. As it is ramping up to full speed, it hits 50Hz and quickly accelerates to 54Hz. It still hits critical speed, but goes through that speed fast enough to keep the pipes from shaking excessively.

Unfortunately, in the groundwater and irrigation industry nobody is going to recognize this problem and if they do, they aren't going to pay the money to have a vibration analyst come out and identify the critical speed. Even if they did, I'm not aware of any drives used in these applications which would allow you to lock it out should it be identified.

I spent nearly 1 year trying to identify the critical speeds of 6 pumps in a pump room using vibration analysis. Once the speeds were identified on each pump, I still had all the piping that had critical frequencies. It seemed it would never end!

I have been on one jobsite with this problem so far and the answer was... add torque arrestors when you have pipes resonating all the way from the pump into the house.

[rebember]

I am also not sure why a VFD drive would provide less overall efficiency when matched to the load characteristics than any other possible solution.

[Cary Austin]

Well then, you just need to do some more reading on this web site.  There are plenty of articles here that show why a VFD is all hype and no substance.  If you want to throw good money away, then get a VFD.  A Cycle Stop Valve will do a better job and give you constant pressure without all the headaches and problems of a VFD.