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226

Pumps, Wells, Tanks, Controls / VFD Soft Starter not soft enough

« on: March 13, 2007, 08:06:50 PM »

I spent the day at a rural water system in north Texas.  They are trying to use a couple of VFD’s as soft starters for two 40 HP Berkeley centrifugal pumps.  5,000 feet from the pump station to a stand pipe, through a 6" main, with distribution all along the way.  Pump has got to build 48 PSI before it starts moving water against the static head of the stand pipe.  3500 RPM pump doesn’t build 48 PSI until it reaches 2700 RPM.

Programmed to take 30 seconds to start up, the VFD spins the motor for 25 seconds before it reaches 2700 RPM.  Then the last 5 seconds gets it to 3500 RPM and the pressure gauge pegs out over 100 PSI, and slowly comes back to about 78 PSI fairly steady.  

We changed it to take 2 minutes to reach full speed.  The pump rattles through about 3 critical speeds during the minute and 40 seconds it takes to reach 2700 RPM.  The last 20 seconds is really all the soft start there is during 2 minutes of ramp up.  20 seconds is really not enough to stop a pressure spike.  The pressure quickly went to about 90 PSI before settling back to 78 PSI.

Then we tried ramping it down slowly.  Told to take 60 seconds to ramp down, nothing happened for about 10 seconds.  Then the pressure dropped off so fast, there wasn’t much difference from just cutting off the power.  The system dropped from 78 PSI to 10 PSI, bounced back to 80 and then hit 0 or lower.  The gauge bounced back and forth, subsiding a little each time for about 2 minutes, until it steadied out at 48 PSI, which is tower pressure.

The VFD or soft starter causes the pump to vibrate considerably, spending too much time going through several critical speeds.  The whining noise as the pump ramped up, was so loud that it drove the water operator out of the building each time.  The pressure bounces around so much, that pressure control to start and stop the pumps and alternate between the two would not work so, we were operating the pumps on manual.  Now they have to buy a telemetry system to operate the pumps from the stand pipe 5,000 feet away.  

At least the motor had a sticker on it claiming “Inverter Duty Voltage Spike Resistant Windings”.  This will help with the 2,000+ volt spikes sent to it by the Drive.  There was no load or line reactor type filter so, the odd numbered harmonics are being fed back into the power grid as well.  No grounding brushes on the rotor so, I am sure the ball bearings will be damaged by electrical fluting from the EDM currents very soon.

They are adding another stand pipe to the system and drilling another well.  The control system is going to get crazy.  This is not over.  I will let you know what they do.  I got some great footage.  Will be making a short video with it soon.
Cary

227

Pumps, Wells, Tanks, Controls / What Size Pressure Tank Do I Need

« on: January 23, 2007, 08:32:18 AM »

I have a 1 HP submersible pump that delivers 20 GPM. My pressure switch turns on the pump at 40 PSI and off at 60 PSI. I have already purchased a CSV1-50. I have a 3 bedroom, 2 bath house. My irrigation system has three zones, one is 3 GPM, one is 8 GPM, and another is 16 GPM. What size tank do I need?

228

Pumps, Wells, Tanks, Controls / Homeowner VFD or CSV

« on: January 23, 2007, 08:11:13 AM »

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