AB140m

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paulengr

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As long as it has overload capability. The VFD has to have it's own short circuit protection and protects the output wiring. If you didn't need shut off capability the most common approach is to put individual overload relays on each motor and series the NC contacts back to an enable input on the VFD.

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ptonsparky

ptonsparky

Tom
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The enable part is what is causing me grief. We have fans stretched across a 700' building each with manual motor starters tapped from a single feeder. Plans are two pump panels or two VFDs if pricing is decent. I know we don't want to be cycling fans ON manually after the VFD is up. Suppose operator training would do any good? Typically the only time that would be a problem is after replacing a faulted fan.
 
Jraef

Jraef

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There is a special version of the 140M called the “D8V” that is specifically designed to operate in the high harmonic content output of a VFD without nuisance tripping. If you use the standard versions, that is the potential problem; the harmonics in the output will cause the bi-metal elements to heat up disproportionately to the motor working current and nuisance trip. That in itself is not necessarily a problem because they trip sooner than they should, not later. But the problem becomes the human response to that when you have an adjustment dial; people will crank up the dial to avoid the nuisance, which can then let the motor be damaged when there is a real overload condition. If you have total control of the maintenance process and can ensure that the “crank ‘er up” mentality is controlled, then you can safely use the regular versions. Just be aware of the possibility of nuisance tripping. The D8V version has been calibrated to use downstream of a VFD at up to 4kHz carrier frequency and down to 25 Hz output speed.
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Jraef said:
There is a special version of the 140M called the “D8V” that is specifically designed to operate in the high harmonic content output of a VFD without nuisance tripping. If you use the standard versions, that is the potential problem; the harmonics in the output will cause the bi-metal elements to heat up disproportionately to the motor working current and nuisance trip. That in itself is not necessarily a problem because they trip sooner than they should, not later. But the problem becomes the human response to that when you have an adjustment dial; people will crank up the dial to avoid the nuisance, which can then let the motor be damaged when there is a real overload condition. If you have total control of the maintenance process and can ensure that the “crank ‘er up” mentality is controlled, then you can safely use the regular versions. Just be aware of the possibility of nuisance tripping. The D8V version has been calibrated to use downstream of a VFD at up to 4kHz carrier frequency and down to 25 Hz output speed.
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Thank you.

IDK why I can’t get a timely response from my local dealer. One would think the potential 200 of those would warrant some sort of response.
 
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petersonra

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Jraef said:
Starting / inrush current of adding a motor to an already running VFD is potentially dangerous to the transistors of the drive due to high di/dt.
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In the case of turning on a small motor on a large running VFD that I can't imagine it is going to matter any. I would agree if it was a 1HP motor and a 1HP drive. But we are maybe looking at dozens of small motors here on a single large drive.
 
Jraef

Jraef

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petersonra said:
In the case of turning on a small motor on a large running VFD that I can't imagine it is going to matter any. I would agree if it was a 1HP motor and a 1HP drive. But we are maybe looking at dozens of small motors here on a single large drive.
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It's the rate of rise of the inrush current that's the issue, not the size of the spike. It can cause the transistors to self-commutate (turn themselves on) when not commanded to, which then cascades problems leading to their demise. A load reactor on the output of the VFD would help lessen that possibility.

But no matter what, no VFD mfr that I am aware of will say that it's OK to close a switch into a motor on the output of a running VFD, no matter how small the motor is compared to the VFD size.
 
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Cow

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If you're putting these in a dairy, it gets tough with EMF if they're using RFID ear tags on the cows.

We've been doing them lately with Lenze ACTech Nema4X VFD's right on the fan with a short chunk of VFD cable right to the motor. No issues with EMF with 70 of them in a holding pen so far. We've had several drives blow up though for a reason the manufacturer hasn't been able to determine yet.....I'm told. Obviously, this is a separate issue though.
 
Jraef

Jraef

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ptonsparky said:
If they decide on the drives they will be in an attached building. How do the drives affect the tags or visa versa?
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Not sure why the tags would make a difference, but there is lots of documented evidence of the Common Mode Noise created by VFDs causing cows to quit producing milk because they can feel a sensation in their teats when hooked up to the milking machines. The trick is to be fastidious about all ground connections and shield grounding, use what are called "Common Mode Cores" (ferrite rings) on the output conductors and in some cases to have shielded drive isolation transformers feeding the VFDs. I have a friend in New Zealand that spent a LOT of time and money investigating this because it was causing dairy farmers near him to lose revenue.
http://www.lmphotonics.com/farm/dairy-shed.php
 
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Cow

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ptonsparky said:
If they decide on the drives they will be in an attached building. How do the drives affect the tags or visa versa?
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I'm told it's affects the devices trying to read the cows ear tags. The VFD and output wiring are basically like a giant FM antenna that cause interference issues. The closer the VFD and shorter the motor leads, the less interference.

Over here, they read the ear tags on the milking carousels for individual cow statistics, they also use the tags to automatically open and close sort gates to sort cows into certain pens, they are used for body condition cameras, and on and on. In the freestall barns, they have activity sensors to monitor for cows in heat for breeding purposes and the employees also use hand scanning RFID wands for identifying and working with the animals directly.

As you can tell, they use the RFID tags for tracking almost everything.

If the farm you're at doesn't use RFID ear tags, or isn't planning on doing this anytime in the future, then it's not a problem.

https://www.valleyvet.com/ct_detail.html?pgguid=C2ECD51C-D599-4BB1-8B06-E73CF9633B99.
 
Jraef

Jraef

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[Intercom announcement] "Uh Bessie, the system is saying that you are a quart low today. Everything all right girl?"
[Bessie] "Mooo..."
[Intercom] "Well, pick it up or we're making a reservation for you at the McDonalds spa..."
 
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paulengr

Senior Member
Some truth here. Common mode issues are caused by failing to run a separate EGC directly between the VFD and the motor frames. This is not optional and bonding through conduit is not good enough. Nothing to do with ferries that are really just cheap reactors.

Second is that beyond about 10-100 feet and this distance is drive specific you will have issues with reflected waves. Based on the application I would assume this is an issue. The best solution out there is a sinus filter but a close second is a dc/dt filter. Output reactors reduce output by about 5% and do little to help and the cost is not much different from a dv/dt filter. A DC choke works really good too, comparable to the dv/dt filter at 1/4 the price but not all drive manufacturers have one available. On the line side it depends on how much of the load on the transformer is the VFD. Again a DC choke makes a big difference but alternatively an isolation transformer does a great job and eliminates all odd harmonics.


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synchro

synchro

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Chicago, IL
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Cow said:
I'm told it's affects the devices trying to read the cows ear tags. The VFD and output wiring are basically like a giant FM antenna that cause interference issues. The closer the VFD and shorter the motor leads, the less interference.
.........

https://www.valleyvet.com/ct_detail.html?pgguid=C2ECD51C-D599-4BB1-8B06-E73CF9633B99.
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Those readers and tags are on the LF (low frequency) RFID band with carrier and modulation sidebands in the vicinity of 130 to 140KHz. So filtering of the VFD output to get sufficient attenuation at this frequency (including the common mode) may be necessary to reduce interference if such RFID systems are used. Conduit and even twisting wires to reduce magnetic coupling would likely help. And reducing conductor length to the extent possible as mentioned above will also help.

I'm very familiar with UHF band RFID but not with LF band that uses near field magnetic coupling between coils (instead of far field coupling and resonant tag antennas at UHF).
 
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