Variable Frequency Drives (VFDs)

What, specifically, would you like to know? Do you have a basic understanding of VFDs, or are you just starting out? What is your application?

The VFD handles ventilation equipments; air handling units and air-condition units. It frequently burns out motor drives. I have troubleshooted this problem, but have not determined why. Most of the time, I put the VFD in manual mode because; the auto mode sends a high ampage to the motor, which causes it to burn out. Any advise will be appreciated.

I wonder why you´d want to a use VFD on a submersible pump.

A submerged pump always has a flooded inlet. If you want to control the flow, throttle the inlet, or operate a bypass. These are cheaper than VFD

WITH OUT GOING IN TOO DEEP , SUBMERSABLE PUMPS UNLESS VERY SPECEIALY DESIGNED WOULD LOT LEND OR TOLERATE THE INLET RESTRICTION. BYPASS FLOW WASTES A LOT OF ENERGY. GENERLLY YOU WILL SEE THROTLED DISCHARGE USUALLY IN THE FORM OF BACK PRESSURE SUSTAINING VALVE , AGAIN WASTE OF ENERGY. SO FOR THIS APPLICATION THE VFD IS THE BEST SOLUTION IF FLOW / PRESSURE CONTROL IS REQUIRED. SEVERAL RESTRICTIONS ARE INVOLVING THE PUMP AND MOTOR COMBINATION BOTH TO PREVENT LOSS OF WARRENTEE AND DAMAGE TO THE PAIR. ACTUAL DESIGN REQUIRES A SIGNIFICANT LEVEL OF DESIGN WORK , AND SHOULD NOT BE TAKEN LIGHTLY

Yes, it is wasteful, however it can be simpler and more reliable in a situation where you can tolerate the waste. With 1000's of horsepower, waste becomes a significant economic factor. There is also the risk of cavitation induced pitting.

Owww! My eyes, my eyes!

Is your Caps Lock stuck? Could you please avoid using all caps in your posts? It's a little difficult to read.

As for the post...we installed a soft-starter in our deepwell pumps. The reason being that we experience quite a strong hammer in the pipes when the pump starts up. Putting in the soft-starter eliminated the problem. Technically, a soft-starter functions like a VFD only during starting and stopping. Could that be the reason for your idea? If not, and you actually want to control the flow coming from your pumps, I don't see a problem with using a VFD.

For a lesson in VFDs, try typing "variable frequency drive" +tutorial in a search engine like Google. Include the quotes and don't forget the plus sign before tutorial. That will limit the number of hits. I won't give any info here since VFDs is a large subject.

I don't know what Hadi's application is but I'm working on a project that has 2 each - 1200 HP, 6600V, submersible pumps that at 1100+ meters deep in the Gulf of Mexico. Siemens VFDs. These are wellhead booster pumps that (supposedly) will extend the life of that particular field by 3 years. Is that what you're working on Hadi?

Ted

Yes.

Dear Hadi,

please, specify your requirement! Because it's a long explanation about VFD, or use search engine google type variable speed drive.

regards,

Hadi,

If you haven't found the info you need and would like further help with your application you can always contact the various manufacturers. They offer assistance to help you select the proper VFD for your application. Rockwell Automation/Allen Bradley is a company I've dealt with many times. Call 1-800-480-1223, which is the Milwaukee office and see if they can help you. If you've settled on a different manufacturer, such as Siemens, ABB, etc. contact them as well. Most of these companies offer free tech and design support. ABB has always been very helpful as well over the years in my dealings with them. Allen Bradley does have a yearly charge for certain support. Hope this helps!

The suggestion to do a google search might help. If your company or the company you are working on the project for, are currently using a certain brand of VFD's, you should check with that manufacturer for possible education materials.

http://www.ab.com/ go to literature library, drives, general information

http://www.abb.us/drives click on training

Depending on the size of the application, VFD's can offer some cost savings over a period of time. This is of course supposing the load requires less than the pump's capacity. In projects I have done, we use a pressure transmitter for feedback and maintain a constant system pressure by varying the pump speed.

If you are only trying to reduce hammer, a softstart might get the job done. Personally, I have never had good success using softstarts on variable torque loads (fans and pumps). The good softstarts with all the features to make them applicable under varying circumstances are too close to the cost of a VFD for me to mess with.

Good day Hadi. Log onto a Siemens website or contact a Siemens office near you to get all the info your require on VFDs. I think they have the best product on the market.

Warning: VFD must be exactly selected to the motor which is suitable for this type of speed control.

If control is done in On/Off (two-position;: start run - stop) mode the given solution with the soft-start is the best.

VFDs on submersible pumps is a common energy efficeincy measure at waste water treatment systems. They also give plants a better handle on the influent flow for the plant. There are many papers on energy efficiency at waste water plants.

VFDs are a common solution to address variable demand for municipal water pump stations. We have them incorporated in most of our stations designed in the last decade. It is cost effective now days and energy efficient for these continuously running variable demand systems.

What causes a VFD motor to burn out? I had two that burned out recently and replacing them were very expensive. As well, I had a VFD to send a high amperage signal to another motor and burned out this motor. Any feedback will be much appreciated.

LOL

How did that VFD "send" that high amperage signal to the other motor? Express mail perhaps?

Wow, the things people come up with....

The most likely cause of your original motor damage was from a phenomenon called "standing wave generation". Much has been written about this and Google is your friend. But in a nutshell, the high speed pulsing of the transistors that comprise a VFD output causes an interaction with the capacitance of the cables feeding the motor. That interaction combines into a slow wave that travels up and down the conductor, building upon itself until eventually it reaches a voltage level sometimes as much as 4 times the fundamental. So on a 400V system, you can easily see voltage pulses of 1600V. Unfortunately, most standard motor insulation is rated at only 1000V, so eventually the pulses, however small in current, cause pin-holes to form in the winding insulation and once that happens, the windings short out quickly. The damage will usually be seen in the first turn of the motor windings, a tool often used in diagnosis because it is so well known now. You can ameliorate the problem by either using insulation in your motor windings that is rated for 2000V, using a filter on the output of the VFD to slow down the rise time of the pulses, or use specially designed "VFD cable" that prevents the capacitive coupling from happening in the first place. Most prudent users employ a combination of these methods to be sure.

As to your "high amperage pulse", I'd hazard a guess that when Motor 1 shorted out and died, the fault transmitted back into your line feeding everything and motor #2 just got hit with a spike that it couldn't handle. The VFD did not "send" it, it just did nothing to prevent it.

By the way, it's considered bad form to hijack someone else's thread. Start your own next time.