RFI & dairy cattle

[ptonsparky]

A customer with Dairy has commented that VFDs produce RFI that damage the immune system on cattle causing loss of production, etc.

New one for me. Anyone with experience in this area? We want to put VFDs on two submersible pumps.

 

[831]

Mad cow???

Very new to me, but you never know.

 

[ptonsparky]

need some help on this one.

need some help on this one.

A salesman has already sold the customer an item to solve all the problems with rfi. (Not here or installed yet.) Looks like it takes care of ground loops, transients, voltage surges, lightning strikes and reduces his POCO bill at the same time.

www.ep2000.com Try looking at the application guide under downloads.

Sounds to good to be true but at $25K it should be.

Animals are suffering from sore feet, etc. Salesman told him it was not stray voltage, but RFI and it builds up over time, causing problems a few years after construciton.

 

[charlie b]

You would do well to advise that customer that, despite any announcements from Chicken Little, the sky is not, in fact, falling. That saleman has done your customer a major disservice, in order to reap the benefits of a large commission. I am not saying that power quality is not real. But it is not always important to every situation, and it is not always worth spending money to correct. In some situations, and I strongly suspect that a farm is among them, power quality issues certainly exist, but they are so small as to be insignificant.

RFI, or "radio frequency interference," is not related to power quality in a home (or farm) electrical distribution system. It is not created by a 60 hertz power system, and it does not impact a 60 hertz power system. It absolutely does not, Not, NOT "build up over time." The notion that it is RFI that is causing harm to animals, and that it is a problem with the power quality of the electrical system that is creating RFI, and that spending vast sums of money to improve power quality will save the animals from future harm, is, in my opinion, criminal, a scam, an attempt to "steal" money from unsuspecting and trusting victims.

 

[winnie]

One would imagine that a dairy farm would already have more BS then they can handle, and would not need to purchase more.

VFDs produce all sorts of nastiness.

VFDs operate by rectifying the incoming supply to DC, and then 'switching' this DC to produce duty cycle modulated high frequency square waves, sending this square wave voltage to the motor. The square wave frequency is perhaps 2KHz to 20KHz, and the switching transitions are perhaps 0.2 to 2 uS long. The DC rail voltage for a 480V system is about 700V.

A 2KHz +-350V square wave will couple quite a bit of current to ground via the capacitance of the motor. This means that even with _perfect_ insulation, you will get current flow to ground. This current flow could cause problems.

The rapid switching transition with high voltage is by its nature a high frequency event. Even though the switching frequency is in the low kHz, the 'edges' have lots of radio frequency components. This RF can couple to sensitive systems. I highly doubt that a cow is particularly sensitive to this switching noise...but other things may be, including communications equipment or automation systems.

The switching frequency is right in the audio range. The switching current flow can couple to metallic objects, producing audible noise which can be _very_ annoying.

I would not be at all surprised if a VFD could in some subtle fashion cause problems for sensitive livestock. But I would be very leery of trusting unsupported product literature full of lots of technobabble prior to spending money to fix a potential problem.

-Jon

 

[zbang]

"Gentleman, I have here the finest Serpent Lubricent to be found in Nature, and you may posess a bottle of this wonderful elixir for the surprisingly low cost of only 25,000 US dollars."

WTF is a 'spectrum multiplier', anyway?

 

[dbuckley]

The real issue with dairy farming is that stray currents do cause loss of production. The cows dont like being part of Kirchoff's law.

 

[ptonsparky]

I am inclined to the area somewhere between Charlies thoughts and Zbangs especially on the claims made by this company.

A little further searching brings up http://www.strayvoltage.ca/Paper.htm where they are saying do not use VFDs at all on a dairy farm because there is no way to consitently deal with the RF.

 

[chaterpilar]

I work with a company which has several dairy farms with 25000 cows in the largest one, we never had problems using VSD.

We use VSd to maintain constant pressures in spray lines..never had any issue, and there is one in every cowhouse.

i also measured for any stray voltages and found none.

good luck !!

 

[iwire]

Welcome to the forum chaterpilla.

 

[ptonsparky]

I might add that I was not the original EC. I was contacted a few years ago by the pump installer to alternate the two submersibles and give warning when one of them failed to start. We were tring to sell VFDs for those pumps when this subject came up.

I am not a stranger to stray voltage chasing but it has been a few years.

 

[ptonsparky]

Boy, just tell a Dairy owner you are a little suspicious about his spending $25K, and you get phone callls from all over the country. Should be an interesting next few days.

 

[boater bill]

About a year ago this same question came up. The answer then and now is the farmer is being sold something that makes great fertilizer, but doesn't help milk production.

 

[boater bill]

http://forums.mikeholt.com/showthread.php?t=82014&highlight=cattle

here is the thread i was thinking of

 

[cschmid]

there is alot on these issues here are a couple of links..

http://www.egr.msu.edu/age/aenewsletter/1_jan_feb_03/tinsey1_03.pdf

http://www.mikeholt.com/mojonewsarchive/SV-HTML/HTML/Thoughts-on-Stray-Voltage~20050506.php

http://strayvoltage.org/stories/index.php3?Story=20000709_dream.inc

good luck with your convincing the farm of the truth..hope your sales pitch is better than a 25k sales pitch..

 

[Jraef]

The phenomenon of stray voltages affecting dairy cattle has been well documented for years, long before the advent of VFDs. It first came up with the advent of inductive well tank level controls; livestock would refuse to drink from galvanized water troughs because they became a better path for the poorly grounded probes. No water = no milk. It is always a grounding issue, NOT one of RFI. So IMHO the RFI component of this argument is just a lower quality of manure than what he already gets from the cows.

How harmonics can come into the picture is when you couple the stray ground voltage effects to the fact that it is also well documented that VFDs can create capacitive voltages in the rotor that can build up in their attempt to travel to ground across the bearing races, causing fluting of the races and/or rapid bearing deterioration. http://www.est-aegis.com/about_aegis.htm

So it isn't a great leap to think that if you have a ground loop problem at your dairy to start with, AND a VFD on a motor without the proper grounding brushes (to keep the voltages from building up), then the VFD could indeed be causing additional not-before-seen problems with the cattle. That can still square up with chaterpillar's observation however, because he may have had a good grounding system and VFD rated motors with shaft grounding brushes, so he had no problems.

But all that said, this magic $25K box is probably worthless in fixing it. What he really needs is for someone to get involved in making sure he has no ground loops in the dairy where the cows are being milked, THEN make sure he either uses a newer VFD rated motor (ensuring that it is one with built-in shaft grounding technology), or retrofits his motors with grounding brushes. It will cost a LOT less than $25K. As others have said, this isn't a condemnation of power quality mitigation, some issues are very real. But just because it is real in one application doesn't automatically translate to every one, and the guy tossing in this hooey about RFI making the cows sick would make me want to run the other way. That part is the tactic of a scam artist.

 

[ptonsparky]

Took first visit to area where suspect drives are located. 23 in all. PVC conduit to motors but plain old romex to all the lighting fixtures in the freestall area. Standard 4"squares everywhere. NEMA one panel(s). Ground loops up the ying yang. No bonding of the rebar as far as anyone remembers. Net current problems on various conduit runs. Appers to be improper bonding of transformers. :grin: :grin: :grin: :grin: etc, etc

Karl, how many milligaus before cows are bothered?

 

[steve66]

A salesman has already sold the customer an item to solve all the problems with rfi. (

I just ordered one for myself too. According to the manufacturers brochure, it will also make my kids start behaving, and stop backtalking their mom :smile:

Animals are suffering from sore feet, etc.

That's not supprising. When is the last time you saw a cow sit down:smile:

I'll believe all this stuff about stray currents affecting cows when I see some scientific evidence.

Steve

 

[winnie]

Stray current is known to affect cows.

Proper methods of dealing with stray current are also well known.

The issues under consideration are: 'can VFDs introduce or exacerbate stray current issues'? and 'can the ep2000 box solve the problem, or would other methods be better?'

IMHO a VFD could make neutral-earth voltage worse, by several mechanisms: capacitive coupling of switching frequency, input rectifier harmonics, switching current coupling to rotors, etc. Capacitive coupling could introduce stray currents which would show up as stray voltages, etc.

With all of that said, I don't see any problems that would not be solved by proper grounding and bonding, possibly with the design enhancements (features not required by code) of 1) using a separate EGC rather than combined EGC/grounded conductor for outside feeders, 2) using _wet_ rated insulation systems in _damp_ locations 3) more careful balancing of line-neutral loads or substituting line-line loads for line-neutral loads.

-Jon

 

[weressl]

ASD's (Adjustable Speed Drives as per IEEE definition) do cause the rise of harmonic components in the ground current and do cause false tripping of gound fault protective relaying if those do not have harmonic restraint designed into the circuitry. So if - a BIG if - we give validity to the previously cited "stray current/voltage" effects of electrical system on dairy, then the use of ASD's would increase the suspected cause. (I always wondered about these reports as to why only the dairy industry seem to be suffering from these effects?)
Appropriate installation of the ASD's will minimize the effects, such as approved motor, cable lengths installed according tot he manufacturer's stated limits and higher insulated (2000V) triple bare ground conductors spaced equally between the phase conductors are a must. Shaft grounding is really only needed on large frame motors, say over 75HP. Run a separate grounding conductor with the cable, if possible, drive a ground rod at the motor and connect the motor and the conductor to it. This aill minimize equipotential difference between the two areas.
The salesman maybe selling a usefull device, but have no clue about how it works. There are devices that inject harmonics to cancel the others based on the same principle as the noise cancellation headphones.
Animals are sensitive creatures, but I would venture to say that the chemical additives, artificial hormones and the overmedication make their system so whacked out that even the slightest external stimulae would cause disstress.
Again, I strongly recommend the engineered application of ASD's.