vfd booster pump control 3

[evan63]

WE have a problem with water pressure at our plant.The pressure ranges from 70psi to 40psi and often there is a significant enough change in pressure to shake the water lines.The booster pump we have is driven by constant speed motor at 1750rpm which we would like to be able to control the speed and try to maintain a smoother water pressure.We
have installed a vfd(Yaskawa G515) and inverter duty motor for the booster pump.The way we are controlling the vfd is by a pressure transmitter(4-20ma)signal insalled on water line, to a honeywell controller(udc2500) and have the honeywell control the vfd and tune the PID on the controller so there is the correct response.Do you guy's think this will work and if you have any suggestions I would appreciate the advise.

 

[dpc]

Maybe of some interest:

http://www.cla-val.com/pdfs/B-59.pdf

 

[Valvecrazy]

I have the same banging problem at concrete batch plants. They weigh the water going into the batch and as soon as they get the correct amount, an air operated valve slams shut. This causes a tremendous water hammer all the way to the pump system. We have learned to use accumulator tanks or stand pipes just prior to the air operated valve. It is important that the inlet size to the tank be the same as the pipe line size. Normally we just place a tee before the air operated valve and stub up a pipe with a cap on the top. On a 4" line I use a 4" riser pipe that sticks up 4' tall with a cap on top. The air accumulates in this high spot and gives some cushion when the air operated valve closes. Then it also requires a pump control valve that is fast enough to react to sudden changes in pressure. Water hammer goes away. This is where a VFD usually reacts so slow that it perpetuates the pressure bounce and keeps it going.

Also DickDV, here is an example of why most motors running on VFD should be derated. A customer has a 100 HP turbine pump. Service factor amps are 137. When running across the line the full load is only 124 amps as the incoming voltage is 485. When running on the drive the voltage to the motor is only 462. This makes the full load amps 138. The drive manufacturer upsized the drive with no different effect. The drive manufacturer finally said that was the best they could do, and if the owner did not want then motor running in the service factor, he need to derate the motor by installing a 125 HP.

 

[waross]

485 volts at 60 Hz. = 8.083 volts/Hz.
462 volts at 60 Hz. = 7.7 volts/Hz.
Did you try configuring the VFD for motor voltage = 485?
respectfully

 

[Valvecrazy]

The no load incoming volts is 505. The electric company and the drive company do not recommend increasing the voltage off the transformers. At load it pulls down to 485 volts. According to the three different techs sent out by Square D, there is no way to ever get the same voltage out of a drive as you put into it. It was much better when we disconnected the line reactor but, still lost about 12 volts just through the drive. To much harmonics not to use the reactor and it brings the voltage at load down to 462 and the amps up to 138, just over the service factor.

We could trim the pump but, we need the maximum performance. The pump will do what we want when running across the line. Just heats up the motor and trips out when running on the drive.

 

[DickDV]

Sorry, valvecrazy, but several things are wrong with the scenario you describe. First off, there is no reason whatever that the max drive output voltage has to be 462 on a 485 volt line. The drive is simply not programmed correctly.

Second, you didn't say what the motor nameplate voltage is. I know that pump motors are a world of their own but, if the nameplate is 460V, you should be able to get the full load out with only nameplate amps. If not, the nameplate values are not trustworthy. On the other hand, if the motor is nameplated 485V as you seem to imply, you have an odd bird indeed, not at all typical of normal duty motors.

Third, if you are sizing the motor based on service factor amps rather than full load amps as is so often done in the pump world, then the drive will not be sized correctly if based on hp. In fact, as a general rule, drives should be sized on amps, not hp. Whoever sized the drive as you describe, simply doesn't know enough about the drive/motor world to do the sizing based on, first, continuous amps, and then, short-term overload amps.

As for sizing the motor, in pretty much any application including pumps, sizing motors based on hp is a high-risk venture too. Motors should be sized on continuous amps and then, short-term peak amps. As in drives, you take the short cut and you pay the price. Experience will teach you a better way if your eyes are open and your mind is receptive to new knowledge.

 

[Valvecrazy]

My eyes are open and my mind is receptive to new knowledge. That is why there is a drive on this pump and I am in a bind. The drive was already upsized from 100 HP to a 125 HP, didn't make any difference. The capacitor bank works like a battery, you can't get more voltage out than you charged it with. The line reactor is a filter. You can't filter anything, water, electricity, etc., without losing something. I saw the meter, there is over 20 volts less when the filter and drive are connected.

It's a 480 volt motor and Square D sized and resized the drive, and it's still running above the service factor. If you can tell me how to program the drive to output higher or at least as high as the incoming voltage, I would greatly appreciate it. I can pass it on to the manufacturer and then maybe we can get the amperage below the service factor.

 

[DickDV]

valvecrazy, I suspect that the reactors are the culprit here, not the drive. It is unusual for a drive to loose more that 3-4 volts from input to output.

You mention a motor-lead reactor but I'll bet there's a drive input reactor built into the drive as well.

You should contact the major reactor manufacturers for better solutions to both the input harmonics suppression and the motor lead filtering. There are other technologies out there that do at least as good a job with less voltage drop. You may also find that raising the carrier frequency on the drive output will permit a lower loss filter design as well.

Major manufacturers are TCI (Transcoil Inc.) and MTE (Milwaukee Transformer and Engineering). Both are located in the Milwaukee WI area and have websites.

Good luck finding a solution.