A simple question I hope. This large dairy facility in southern California is being fed with a delta system without a primary neutral. There are five pad mounted transformers throughout the site.These transformers are in a wye wye configuration.The primaries are 12470GY/x7200GY/4160 and secondaries are 480/277. This dairy has been operating for 15 months with several problems associated with stray or transient voltage.The question is can you feed a wye wye transformer with a delta system without a neutral? Any comments would be appreciated.
Transformers on dairy farms
- Thread starter Deke12754
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mdshunk
Senior Member
- Location
- Right here.
Re: Transformers on dairy farms
No, seriously, utilities normally use wye-wye transformers for services since they area cheaper than delta wye. There's nothing about a wye-wye transformer or it's associated connections that will cause any stray voltage issues any more than any other type of transformer will.
I've been involved with 7 different dairy stray voltage related issues and only one was traced back to the utility (loose secondary neutral). The other 6 were the cause of something on the farm. You're talking about a bigger farm that I've ever had to deal with. Sounds like fun.
Sure, wye not?
No, seriously, utilities normally use wye-wye transformers for services since they area cheaper than delta wye. There's nothing about a wye-wye transformer or it's associated connections that will cause any stray voltage issues any more than any other type of transformer will.I've been involved with 7 different dairy stray voltage related issues and only one was traced back to the utility (loose secondary neutral). The other 6 were the cause of something on the farm. You're talking about a bigger farm that I've ever had to deal with. Sounds like fun.
rcwilson
Senior Member
- Location
- Redmond, WA
Re: Transformers on dairy farms
Unbalanced secondary loads will cause primary neutral currents to flow in the ground back to the substation source unless the transformer has a delta winding.
Example: assume a 200A, single phase 277V load on A phase. 7.7 amps will flow in the A phase primary winding. (200 x 277/7200 = 7.7 amps). Assume no load on B or C phase. That means there can be no current in the primary B&C windings. The only place the 7.7 amps in the A phase winding can go is out the neutral and into the ground. That current has to travel in the ground back to the utility substation transformer's grounded neutral.
Any unbalanced neutral currents, including harmonics, will cause ground currents in the primary neutral "circuit" that is the ground.
Usually Y-Y Xfmrs are padmount type, fed with shielded cable or URD cable. The grounded cable shields provide a ground return path for the unbalanced currents.
The Y-Y's might be a source of the stray voltages but I would eliminate other possible causes first: improper neutral groundng, poor gorunds, etc.
edit:
Just saw that you said it was fed by delta system. If any phase imbalance occurs, I don't see how the unbalance current can get back to the ungrounded delta winding.
[ June 08, 2005, 09:06 PM: Message edited by: rcwilson ]
Unbalanced secondary loads will cause primary neutral currents to flow in the ground back to the substation source unless the transformer has a delta winding.
Example: assume a 200A, single phase 277V load on A phase. 7.7 amps will flow in the A phase primary winding. (200 x 277/7200 = 7.7 amps). Assume no load on B or C phase. That means there can be no current in the primary B&C windings. The only place the 7.7 amps in the A phase winding can go is out the neutral and into the ground. That current has to travel in the ground back to the utility substation transformer's grounded neutral.
Any unbalanced neutral currents, including harmonics, will cause ground currents in the primary neutral "circuit" that is the ground.
Usually Y-Y Xfmrs are padmount type, fed with shielded cable or URD cable. The grounded cable shields provide a ground return path for the unbalanced currents.
The Y-Y's might be a source of the stray voltages but I would eliminate other possible causes first: improper neutral groundng, poor gorunds, etc.
edit:
Just saw that you said it was fed by delta system. If any phase imbalance occurs, I don't see how the unbalance current can get back to the ungrounded delta winding.
[ June 08, 2005, 09:06 PM: Message edited by: rcwilson ]
Re: Transformers on dairy farms
rcwilson:
I'm not sure I buy that. I thought about it a few minutes, and realized it would probably take a long time to prove or disprove. (Please don't be offended - I'm the worlds largest skeptic. But I am considering conceding that the world might not be flat ).
I have seen several references to stray voltages affecting dairy cows, and I'm skeptical of that also. Why would cows be any more sensitive to EM fields than people or any other animals?
Steve
rcwilson:
I'm not sure I buy that. I thought about it a few minutes, and realized it would probably take a long time to prove or disprove. (Please don't be offended - I'm the worlds largest skeptic. But I am considering conceding that the world might not be flat
).Hmmm, is it that simple?
I have seen several references to stray voltages affecting dairy cows, and I'm skeptical of that also. Why would cows be any more sensitive to EM fields than people or any other animals?
Steve
rcwilson
Senior Member
- Location
- Redmond, WA
Re: Transformers on dairy farms
Steve - cows are more sensitive than humans to ground currents because their feet are farther apart. For the same current in the ground the cow's legs at 6 feet span a larger distance and feel a bigger IR voltage drop than mine do at 2 feet. (So why don't horses seem to get affected as much?)
Also, cows seem to detect small currents when they are connected to the milking machines. Maybe it's because the milk pathway gives a lower resistance path to the internal organs during milking. My personal experience is that a cow will kick like heck when you touch it with a milker that has stray voltage from vacuum line piping that's carrying some current due to a grounded neutral in a broken light socket. Stray currents in a dairy barn affect the milk production.
On the wye-wye issue: on any transformer, there's no load current in a LV winding unless current also flows in the corresponding HV winding. (Ignore excitation current). When three single phase windings are connected delta-wye, the HV A phase current has a path to flow in the A & B line conductors. With a wye-wye winding connection, it has to flow in A phase line and neutral, or get canceled by B & C currents in the neutral.
Good Luck on the investigation.
Bob
Steve - cows are more sensitive than humans to ground currents because their feet are farther apart. For the same current in the ground the cow's legs at 6 feet span a larger distance and feel a bigger IR voltage drop than mine do at 2 feet. (So why don't horses seem to get affected as much?)
Also, cows seem to detect small currents when they are connected to the milking machines. Maybe it's because the milk pathway gives a lower resistance path to the internal organs during milking. My personal experience is that a cow will kick like heck when you touch it with a milker that has stray voltage from vacuum line piping that's carrying some current due to a grounded neutral in a broken light socket. Stray currents in a dairy barn affect the milk production.
On the wye-wye issue: on any transformer, there's no load current in a LV winding unless current also flows in the corresponding HV winding. (Ignore excitation current). When three single phase windings are connected delta-wye, the HV A phase current has a path to flow in the A & B line conductors. With a wye-wye winding connection, it has to flow in A phase line and neutral, or get canceled by B & C currents in the neutral.
Good Luck on the investigation.
Bob
Re: Transformers on dairy farms
Not sure the cows length has as much to do with it as the low impedance connection to ground and objects of different potential through the teats, mouth and hooves. Those are involved in the big problem areas of milking and feeding facilities. Lots of moisture around, frequently lots of electrical equipment and the combination of the two results in increased maintenance needs.
If you don't believe it can be a problem, think about a situation where every time you wanted to take a drink you got a tingle of electricity. No way around it, no other source of water and you need to drink 50 gallons or more a day. Usually the result is the cows will drink enough to stay alive as we would expect and can even become acclimated to a degree, but don't ever produce as they could without the drag of the adverse situation.
Can't think of a similar situation to explain milking problems
We installed equal potential planes in the milking facilities when they were remodeled to at least make everything the cows can touch while being milked the same potential.
Jim
Not sure the cows length has as much to do with it as the low impedance connection to ground and objects of different potential through the teats, mouth and hooves. Those are involved in the big problem areas of milking and feeding facilities. Lots of moisture around, frequently lots of electrical equipment and the combination of the two results in increased maintenance needs.
If you don't believe it can be a problem, think about a situation where every time you wanted to take a drink you got a tingle of electricity. No way around it, no other source of water and you need to drink 50 gallons or more a day. Usually the result is the cows will drink enough to stay alive as we would expect and can even become acclimated to a degree, but don't ever produce as they could without the drag of the adverse situation.
Can't think of a similar situation to explain milking problems
We installed equal potential planes in the milking facilities when they were remodeled to at least make everything the cows can touch while being milked the same potential.
Jim
Re: Transformers on dairy farms
Thanks for everyones input.Another question I have is that when cycling the 277 volt lighting loads I found 1 to 2 amps at times on metal stalls throughout the dairy.The question I have is "would any electrical engineer design a system such as this". Again an ungrounded delta system without a neutral is what is here presently with 5 pad mounted wye -wye transfomers . The location of this dairy receives only 3 to 4 inches of rain a year. If the ground was "wetter" I think there would be a potential safety issue.What say you?
Thanks
Thanks for everyones input.Another question I have is that when cycling the 277 volt lighting loads I found 1 to 2 amps at times on metal stalls throughout the dairy.The question I have is "would any electrical engineer design a system such as this". Again an ungrounded delta system without a neutral is what is here presently with 5 pad mounted wye -wye transfomers . The location of this dairy receives only 3 to 4 inches of rain a year. If the ground was "wetter" I think there would be a potential safety issue.What say you?
Thanks
jtester
Senior Member
- Location
- Las Cruces N.M.
Re: Transformers on dairy farms
Deke
You have spotted at least two sources of your problem.
First Y-Y transformers must have a primary ground to prevent excessive voltages. You must discuss that with the utility.
Secondly, identify the circuits that put the one to two volts on the piping by shutting off all circuits and then turning one on, checking for voltage and turning it back off. Do this to each circuit, and those that impress a voltage have a problem, either leakage, bad connections, or something like that.
jtester
Deke
You have spotted at least two sources of your problem.
First Y-Y transformers must have a primary ground to prevent excessive voltages. You must discuss that with the utility.
Secondly, identify the circuits that put the one to two volts on the piping by shutting off all circuits and then turning one on, checking for voltage and turning it back off. Do this to each circuit, and those that impress a voltage have a problem, either leakage, bad connections, or something like that.
jtester
Re: Transformers on dairy farms
Did the voltage you found cycling the lights remain or was it a surge from turning them on?
Either would be unacceptable, but I know which I would rather have
We had a setup with 16 small 120 volt motors on one circuit starting together that made quite a noticable tingle between feeders and floor grates while they were starting, which they unfortunately did every 15 seconds or so. The solution was to split the motors into two circuits on two phases. That helped a lot, but I was always told it's best to use "220" equipment instead of line-neutral connected loads like the lighting you describe.
We are on a centertapped delta 3 phase service, supplied open wye/open delta. Primary and secondary neutrals are connected.
Jim
Did the voltage you found cycling the lights remain or was it a surge from turning them on?
Either would be unacceptable, but I know which I would rather have
We had a setup with 16 small 120 volt motors on one circuit starting together that made quite a noticable tingle between feeders and floor grates while they were starting, which they unfortunately did every 15 seconds or so. The solution was to split the motors into two circuits on two phases. That helped a lot, but I was always told it's best to use "220" equipment instead of line-neutral connected loads like the lighting you describe.
We are on a centertapped delta 3 phase service, supplied open wye/open delta. Primary and secondary neutrals are connected.
Jim
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