VFD. multiple motor.long lead length

I have an application in a dairy barn where the customer wants to run his ventialtion fans on a vfd to slow them down and get energy savings. He has seven fans that will start and stop together and run all the same speed so I plan to simply run them all off of one drive and use individual motor protection.

My question is about lead length to the motors. WE could be be talking up to 300-500 feet between the drive and the motors. If I use an output filter on the drive to dampen the spikes to save the motors at this lead length, will that be sufficient or should I have one small filter on each motor? I am trying to think through whether having 7 motors with long lead length compounds the problem if the output filter is rated to carry the current of all 7 fans.

I know buying 1 large drive is probably cheaper than 7 smaller drives, but did you consider if the drive large fails, you lose ALL fans instead of just one? I don't know the application, but in some cases the loss of production because of the failure of ALL fans will pay the difference in a short time, not to mention the replacement cost being much higher on the large drive than replacing just one smaller drive. Also, smaller drives are usually more available than large ones.

Just something to consider.

what is the voltage you will be using?
you may also need line reactor also due to motor lead length.
what is the hp rating of the motors?
with multiple motors, you must use a higher vfd rating.
for example, if each motor is 1/2 hp, the total for 7 fans would be 3 1/2 hp so I would go with a minimum of 5 hp. since the leads are so long you may need a 7 1/2 or 10 hp.
I would certainly goto the vfd manufacturer rep and discuss the application with him.

james

That is definitely something to keep in mind. We do plan to put a bypass contactor in to run all fans at full speed in the event of a drive failure. The control wiring etc. is much simpler this way

James Mcquade said:

what is the voltage you will be using?
you may also need line reactor also due to motor lead length.
what is the hp rating of the motors?
with multiple motors, you must use a higher vfd rating.
for example, if each motor is 1/2 hp, the total for 7 fans would be 3 1/2 hp so I would go with a minimum of 5 hp. since the leads are so long you may need a 7 1/2 or 10 hp.
I would certainly goto the vfd manufacturer rep and discuss the application with him.

james

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This is on 480V 3ph. the motors are 1hp. Can you explain the need of a line reactor and an oversized drive because of the long lead length?

My customer also wants me to quote a 1ph 240V input. Is there complications between having long lead length on single phase supply?

lesmar96 said:

My customer also wants me to quote a 1ph 240V input. Is there complications between having long lead length on single phase supply?

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Other than the volt drop calculation, there is the fact that a conductor begins to act like a capacitor with increasing length. 3-500 feet is not insignificant, you should take these factors into consideration.

you are quoting a single phase VFD I would assume that the fan's are single phase as well.
You can not run a single phase motor on a VFD ( with a few exceptions)
it looks to me like have to replace all the motors as well to run from a VFD.
you can get a single phase VFD to run all the motors but I think you would do better to have a separate VFD for each motor.
if you have trouble finding the VFD you need let me know.

I am quoting to an OEM that is doing basically all new installations. All the fans will be 3ph, we will oversize the vfd to be used as a phase converter. I am basically wondering about whether it is good to use one output filter per motor or one large filter to run all the motors through?

I still think you are better off with separate VFD's for each motor. when you add up all the extra hardware cost ( Line filters, motor protectors ect. ) you will soon eat up the cost difference. whit separate VFD's you will have much better control on the system you could select exactly what fan to and at what speed and one shorts outs you just disable the VFD and the rest will run as normal.

This is probably a dumb suggestion,but, if possible, use individual drives and locate the VFD drive nearer to the motor then run the control wiring back to a central location. You may need a protective enclosure for the drive but you could possibly eliminate the line reactors by being near the motor. Anything more than a couple hundred feet between motor and VFD drive is asking for mystery troubles. I also agree with all that GaryS said in post #10.

lesmar96 said:

That is definitely something to keep in mind. We do plan to put a bypass contactor in to run all fans at full speed in the event of a drive failure. The control wiring etc. is much simpler this way

Click to expand...

lesmar96 said:

My customer also wants me to quote a 1ph 240V input. Is there complications between having long lead length on single phase supply?

Click to expand...

Keep in mind that it's impossible to combine these two! You can't run a three phase motor on 1 phase input. The drive is required to do the conversion.

From past experience, I'm saying the greatest concern has not been addressed...

This is in a dairy barn. The cost of the drives is negligible compared to the expense and grief this farmer will experience over time due to EMI and harmonics on the ground network. Select a quality drive with good EMC filter and install as close as possible to the motor. For these fans you should be able to keep the motor leads less than 1 meter long. Use quality VFD cable with minimum conductor exposed and shield connected at both ends.I know it looks like I'm going over the top here, but we have been involved with stray voltage testing and have been correcting similar installations for years. From what I have all seen, I couldn't sleep at night if I installed a drive in the manner you describe with long motor leads.

I don't have time now for a detailed technical explanation but basically what happens with long motor leads and poor cabling is the harmonics increase and end up on the ground network. This voltage becomes present at cow contact points and a host of problems arise. Mortality, foot, and production.
We have years worth of stories that could be told.

I don't mean to get involved in a brand war but the cleanest (EMC pollution) drive we have found is ABB. I could recommend the ACS355 for your application.

sbaum - +1
I forgot he mentioned dairy, you are correct.
Dairy farms require different transformers to reduce stray voltages.

stray voltages is a big no no.


lesmar96,
its been a while, when you have a 480 volt system with long motor leads , you basically change the motor leads to transmission lines. the drive creates harmonics and the wire also has capacitance. the two combined creates a waveform that starts at the drive and travels to the motor. that harmonic waveform is then reflected back to the drive and is greater than the 480 volt power signal and can damage or destroy the drive. not only that, it can travel thru the drive and back to the main transformer. the line and load reactors absorb a lot if not all of this energy.

If you use individual drives and enclosures, you will need to use NEMA 4X ss316 enclosures due to washdown and bacteria considerations. you will need to look at your washdown chemicals and enclosure reactivity chart to make sure you are using the right one. the food and diaper wipes industries that I am familiar with uses ss 316.

If you use vfd(s), make sure the motors are rated for vfd use, standard motors are not.

james

Thanks for bringing up the stray voltage issue, it is definitely a grave concern on farms and we are feeling our way on the best way to protect ourselves. This panel is quoting to an OEM that is hoping to do a lot of these setups so we gotta get it right the first time.

A filter company recommended an EMI filter for the input and a Choke to suppress the spikes on the output. Do you think this would be sufficient? An additional line reactor would probably be a good idea as well.

Since this is a 480V system and long leads, James, am I understanding that the issue of capacitance in the wiring etc would be less on 230V? Obviously the spikes won't reach as high of a voltage, but the ratio to the nominal voltage could cause just as much trouble.