Ground fault alarm?

[mdshunk]

Anyone got any product recommendations for a ground fault alarm with an ajustable setpoint for a dairy farm application? The equipment will need to be 3R rated, and capable of monitoring the single phase, 800 amp service, comparing the phase currents to the neutral current. This morning, greeted by two dead dry cows, I was able to determine that a faulty waterer was the cause of the deaths, and the graph of the milk production for all the cows for the last 5 weeks makes it pretty clear others were affected. A ground fault monitor, I think, should head off some of this at the pass.

 

[jim dungar]

I have used the Vigirex family from Square D. Because they are zero sequence devices they don't care about the number of phases.

How sensitive do you want to be? The ones on page 7-46 of Digest 174 can go as low as 30mA.

 

[mdshunk]

How sensitive do you want to be? The ones on page 7-46 of Digest 174 can go as low as 30mA.

That's the trouble with what I was able to find quickly. Ideally, I'd like it to be adjustable near 4 milliamps. This is the level at which the farmer says dairy cattle develop sensitivities. That might be an impossible level, given minute permissible permitted leakages in lots and lots of equipment. Since the outdoor disctribution equipment has many feeders leaving it, I might have to monitor each feeder seperately to achieve what I think we want to achieve so that there's no a cumulateive GFP alarm reading. I don't care so much, perhaps, that there's 4ma leakage total so much as I'd be more concerned if one feeder alone totaled 4ma. Totalizing the reading might not be all that beneficial, because I wouldn't really know, for instance, if I had 4ma "normal" leakage for the whole service, or 0ma on all the feeders except one. At this point, maybe you could say that I'm not sure what I want to try to sell, but I'm going to sell something.

 

[brian john]

Standard CT, current relay from Graingers, with adjustable set point Nema 3R box from Graingers.

Set up as a zero sequence through the current relay, this relay has aux contacts.

 

[mdshunk]

Standard CT, current relay from Graingers, with adjustable set point Nema 3R box from Graingers.

Set up as a zero sequence through the current relay, this relay has aux contacts.

There aren't really any suitable relays for that from Grainger. Maybe a current sensing relay, if I was to put a calibrated load on the zero sequence CT.

 

[brian john]

Yes to the current sensing relay... Also a 10/5 CT, use a variac and a resistive load to cal.

 

[iaov]

Marc is this a grounding/bonding issue?? I would think it would take a pretty good wallop to kill a cow. Never did any wiring on a dairy farm but last wifes father was a dairy farmer and he did his own wiring. Ground wires were just a PIA to him.

 

[mdshunk]

Marc is this a grounding/bonding issue??

You betcha. Lack of maintenance is the root cause.

 

[mdshunk]

Yes to the current sensing relay... Also a 10/5 CT, use a variac and a resistive load to cal.

Gotcha.

When you get a chance, can you describe the calibration procedure in more detail?

Is there a certain size and wattage resistor that is most typical to use for this type of arrangement? It seems like the resistor would need to be a permanent part of the alarm assembly, to make the current transformer "work" as a permanent load on the CT secondary, right?

 

[iaov]

You betcha. Lack of maintenance is the root cause.

Sounds like a good oportunity to make some money. Hard to put off fixing things when the live stock starts dying.:grin:

 

[jim dungar]

For current sensing relays I used to use NK Technologies. But I don't think a standard core CT will give you 4mA with any type of accuracy or repeatability.

There has been lots of research done on stray voltage and dairy cows. Check with the Univ of Wisconsin - Madison. Whenever someone asks me for help in this area, I politely decline saying it is beyond my area of expertise.

 

[dbuckley]

Marc is this a grounding/bonding issue?? I would think it would take a pretty good wallop to kill a cow.

The issue isn't killing the cow; a small current of just a few mA is enough to give the cow a tingle in the milking parlour, and then the cow's milk production drops dramatically. So any stray currents in a milking facility are very bad news, and cost money.

Of course, out in the open fields we like to belt cows with 10KV.

 

[mdshunk]

The issue isn't killing the cow; a small current of just a few mA is enough to give the cow a tingle in the milking parlour,..

In this case, they were scared to drink. Less water intake = less milk. His milk check was down over 25K last month.

 

[benaround]

Marc,

Within the last two weeks someone posted a thread about cows not giving

milk because of stray voltage. He found an outdoor vending machine, a recpt.

mounted on a metal sided building, and a few other things that I can't seem

to remember, as the cause, he fixed the items and the milk she came a flow-

ing agian. I know it takes very little current to upset most farm animals. I can

see standing barefoot in the mud as premo conditions. My point is that maybe

while finding the gfi equipment that you are looking for, you could shut down

as much power as you can to ( maybe ) save another cow, or, even get

the milk going agian.

 

[mdshunk]

My point is that maybe

while finding the gfi equipment that you are looking for, you could shut down

as much power as you can to ( maybe ) save another cow, or, even get

the milk going agian.

The problems are fixed already now. That's what I spent today doing. I just want to be able to sell him some sort of alarm for an early warning before the total leakage current gets to the high levels I found. The whole service had 17-18 amps "disappearing" when I arrived this morning.

 

[benaround]

Marc, I should of known that you had already taken care of it. Has anyone

told you latley that you are one hell of an Electrcian.

 

[dbuckley]

In this case, they were scared to drink. Less water intake = less milk. His milk check was down over 25K last month.

Thats the classic case.

This problem has been known of for over four decades, problems that have a direct effect on a farmer's top line, yet still these problems are occurring.

 

[brian john]

ITI Instrument Transformers Inc. (NOW GE sad to say)* makes a GFI relay with low sensing BGFL XXXXXXXXX do a search of the most difficult Web Catalog (GEs). I would post a link but I do not have the time.



*Use to get ITI relays overnight now it takes 4-6 weeks

 

[tom baker]

Marc: Interesting applaication. When you get it done and working, Mike Holt may be interested in sending this out as a newsletter item.
I'd like to see some pictures if you would post them, thanks, Tom.

 

[brian john]

Marc:

I should have asked and not assumed. What level current are you looking for?

If it is posted in my haste to read I missed it. Good old Evelyn Woodhead Speed Reading Course. fails me again twice in 24 hours...JUST GOTTA SLOW DOWN