Hi GITRDUN
I would not accept that, not a chance in hell. It is not a genuine 3-phase Y connection. Frankly, I think it is a cheap fudge or fake which will cost the PoCo virtually nothing. All they would do is switch a few wires around, nothing more. It will not solve your problems (your machines being damaged) either.Ok so some progress maybe. I talked with the city electrician to see about having them switch my transformers over from 3-phase high leg delta to a 3-phase Y. Right now i have three legs at 120V 120V and 208V and all are 240V phase to phase. With the Y setup i will get 120V 120V and 208V but all will be 208V phase to phase. Is this correct?
What you want is a genuine 4-wire 3-phase Y connection with the same voltage on all three phases, using a genuine 3-phase transformer. NOT some bodgy antique Heath-Robinson high-leg delta lashup from 100 years ago. This is what the rest of the world runs with, and what much of America gets as well. Do not compromise on this, do not let them cheat you. Yes, this means they will have to suffer the horrrible expense of actually buying a new 3-phase transformer. Oh, the suffering, the anguish at their bottom line, the paperwork. Tough: you have paid your power bills for years and been served with crap power which has cost you huge amounts of money and frustration. Time for a change.
You now have them admitting there is a problem. They are trying to negotiate the cheapest solution they can get away with - at your expense. Naturally, their opening offer costs them nothing. Nihil illegitimum carborundem!
Cheers
The 200v control voltage is usually reduced after the fact by internal transformer, so make sure the lower three phase is within the tolerance of ±10%.
Each machine should have a manuf. plate somewhere on the exterior stating the power required.
I interpret it that you are getting Y secondary transformers?
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
I am very leery of running any 208V input equipment on a high leg delta. Those stupid things were originally designed for lighting loads and 3PH motors. The trouble is that a CNC or anything with a control board in it uses just one phase to drive the control electronics. Not having a neutral is just asking for trouble since all the current has to go somewhere in an unbalance situation. It ends up as "excess voltage" on another phase - and burning your boards up since they are the most sensitive. I'm just thinking your startup loads (lots of capacitors on one phase, for instance) are unbalancing the transformer causing a big surge. Do you get a big groan from the transformer in the morning?Originally Posted by GITRDUN
I'm with RCaffin - have the PoCo install or rewire the transformers.
A short story.I'm with RCaffin - have the PoCo install or rewire the transformers.
When we bought our property - a farm, we asked the supply authorities for power. In those days they were a government utility which actually served the public, not a private enterprise thing. They asked us what we needed. Now, I happened to know that the small country side road we were on already had problems with the supply: when someone switched on several hot plates on their stove everyone else could see the sag in voltage - brown-out on the light globes. Adding our needs were just going to make that worse. What to do?
So I pointed out that I would be having a large workshop with machinery, and please could I have 3-phase 240 V up to 60 Amps. They gibbered slightly, asked what sort of machinery, then sighed and said OK. There was absolutely NO WAY the current feed could deliver that. So our side-road got a new 3-phase transformer at the junction with the main road: not large, just 250 kVA. Our neighbours all thought we were WONDERFUL!
The moral of the story is that you only get what you ask for, and that a full new 3-phase transformer direct off the HT grid is not really a big deal anyhow. Accept nothing less.
Cheers
Roger
Well i guess i should have elaborated a little. They are talking about replacing the current transformers with new transformers. So i would assume they are going to do it right but not knowing whats what its all over my head.
So someone please tell me flat out in layman terms exactly what type of power connection and transformers i should want here, because when i call to tell them what i want them to install i better know what im asking for.
Herewith my version:
You want a full 3-phase transformer connection to the grid yeilding a sdtandard Y connection: three equal phases of the same voltage plus neutral. What voltage you ask for - check your machines. It is likely to be whatever is 'normal' in America today: somwhere around 110 VAC I believe? Although IF (IF!) you machines could handle it, 120 VAC would be better. Hey, here in Oz we go for 240 VAC! You should emphasise that you do not want anything to do with the old high-leg delta connection as it has been giving you nightmares.
Fortunately, if they are going to install a 'new' transformer, it is likely that you will get real 3-phase power with a Y connection, as I don't think they are using that obsolete high-leg technology any more. It may even be that they are simply not making such transformers any more. Would not hurt to ask, and keep asking, until you get a really clear answer. Equally, it may be that you will get whatever is now 'standard' in the way of voltage - although they can usually adjust the taps on the output to get close to what you want at your switchboard.
If all this works, LET US KNOW!
Cheers
My understanding is that they are talking about installing new transformers to get the Y configuration and completely do away with the high leg delta. Under the Y configuration i end up with one leg that is 208V and the other two are 120V. Would it be better to have three legs that are equal 120V? Or is that not a possibility?
AL - What do you mean by Y secondary transformers?
Hi GITRDUN
GOOD!My understanding is that they are talking about installing new transformers to get the Y configuration and completely do away with the high leg delta.
BAD!Under the Y configuration i end up with one leg that is 208V and the other two are 120V.
YES! That is what the rest of the world does. My 3 phases are all 240 VAC.Would it be better to have three legs that are equal 120V?
In fact, if there is much imbalance between the 3 phases, normal 3-phase motors start to grumble badly. And then I grumble to the supply company and they come and fix it fairly quickly. EQUAL VOLTAGES!
I suspect they are trying to match the old voltages which you used to have. But do not accept that. Go for 3 equal arms. This may mean you will have to rewire some of your machines, but that might mainly consist of taking some small transformers OUT of circuit. If you have been feeding 120/120/208 into your gear, there may well be a small transformer on the high leg dropping it down to 120 V inside each machine. If that is the case you can just take those transformers out. BUT - get a licenced electrician in to check that. Ha - you may find that any licenced electrician will be much happier with 3 equal phases!
Cheers
Roger
Gotcha. This is what gets me lost. Even though in my current high leg delta there are two legs that measure 120V to ground and one at 208V to ground, when measured phase to phase they all equal around 240V. The Wye setup will also have the same measurements when measured to ground but will be 208V phase to phase. So if i can get a 3-phase configuration that all three legs measure 120V to ground, what would they measure from phase to phase? Would it be 240V?
That is what I interpreted you to say, normally you would have 3 phases each with 120v to the Y star point and 208 between any two phases, the star point would be a Earth Grounded neutral.
Al.
Last edited by Al_The_Man; 12-05-2013 at 12:14 AM.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
Hi GITRDUN
You can work it out for yourself. The diagram here is a good representation of how genuine 3-phase works.
Each arm of the Y is one phase. I have used 100 for the length; for 120 V you just scale. The voltage between phases here is 173.2; for 120 V it is 173.2 x 1.2 = 207.8 .
The middle of the Y is the neutral.
Cheers
Roger
PS: we use 240 instead of 120: twice the voltage.
You are correct and once again i was confusing myself and probably every one else as well. That is the setup the power company is talking about installing. Wye Three phases each measuring 120V to ground and each measuring 208V phase to phase.
I told the power co to pull the trigger on that setup so the high leg delta will soon be gone and good riddens. Time will tell if things get better or not. Either way i will post back with my findings to confirm that was part of the problem or to get some more insight from you all.
Thanks for all the help its much appreciated.
Excellent. I predict your problems will subside.
Not at all! Honestly you need to find an industrial electrician or engineer to help you here because doing this via a forum will likely lead to mistakes.
Here is the thing a Y connected transformer installation, properly done, visually looks like a Y in a schematic drawing. With three phase you have three separate windings for each phase. One end of each winding is connected to the other windings. These three leads if you will get grounded. So between ground and the other end of the winding you effectively have around 110 VAC. Or effectively three different 110 VAC systems. From phase to phase you get about 208 volts.
If you want to get accurate numbers look here for some information: Three Phase Transformer Connections and Basics
You can actually have Y connected systems at voltage other than 208 phase to phase. 208 systems are popular where most of the loads are 110 VAC single phase.
A couple of more things.
AL - What do you mean by Y secondary transformers?
The voltage ratings of your machinery means a lot, some machines simply will refuse to run on supply voltage that are too low. You will literally have to review the voltage and current needs of every machine you have.
The second issue is if you have a plant wire for 240 volts and you switch to 208 you might find that some feeders to the machines are undersized. It is a remote possibility but something to watch out for, if the breakers are close you could also end up with nuisance trips.
Maybe I missed something but you said you have two buildings impacted by this issue. Are both buildings running off the same transformer bank? I only ask because if they are powered from two different transformer banks then this upgrade probably won't solve your issue.
A bigger problem might be your switch gear and stuff in your facilities, will they support 3 phase Wye power? Ideally you will want your single phase 110 loads balance across all three phases. I'm guessing that panel boxes might no be set up that way. Putting in an entirely new electrical service could cost you some money, especially if the power company refuses to turn the power back on if they see something they don't like. You want to make sure the power company is happy with you switch gear before you let them do any work.
In any event the reason I suggest consulting a qualified electrician or engineer is that you really want a very good handle on what is involved in this upgrade and more importantly what expenses you will suffer if any.
If neutral to phase is 120v then phase to phase is 120√3 = 208v
By Y I meant delta star transformers delta primary, Star or Wye secondary.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
I am not going into this change without any help. I have an experienced electrician that will be doing all the work on my end of the supply to make sure everything is good and ready to go before the switch is made. I have tried to get him to help me out with this mess for a couple years and he basicly put me off over and over until the city electrician leaned on him a bit yesterday and told him to call me and get things ready to make a switch right now. I have dealt with him many times and know him to be knowledgable and experienced. Although a bit lazy when it comes to getting a big job done. But he is familiar with our shop and knows the ins and outs of our electric setup.
And i do know that all of my equipment is rated to run around 200~240V. All our machines have step up/down transformers in them to adjust the voltage up or down about 20 volts to keep the control voltages in spec.
I do have two seperate buildings running from seperate transformers and both experience the same problem. This switch may make no difference at all but i wont know til i try it. I cant see any real disadvantages besides maybe a little higher electric bill from running at a lower voltage.
Hopefully you will get results.
As you say, most major equipment has local transformation that is adjustable by various taps.
Your electric bill should not be affected as the power consumption should be the same.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
Is this guy a relative? If he isn't there is really no reason to put up with him.
This isn't the type of job you want somebody dragging their feet on.I have dealt with him many times and know him to be knowledgable and experienced. Although a bit lazy when it comes to getting a big job done. But he is familiar with our shop and knows the ins and outs of our electric setup.
Here is the problem I have; you are about to change the service to your plants, possibly to a 208 VAC system, this isn't trivial. I don't know for sure what you are going to, in any event you really should have a document detailing the voltage requirements of every single machine in the plant with the actions to be taking to adjust the machines after the service change has been made.And i do know that all of my equipment is rated to run around 200~240V. All our machines have step up/down transformers in them to adjust the voltage up or down about 20 volts to keep the control voltages in spec.
Your electrical bill is based on power, you shouldn't see a significant change. There may be some losses of efficiency but I'd be very surprised if you see it in your bill.I do have two seperate buildings running from seperate transformers and both experience the same problem. This switch may make no difference at all but i wont know til i try it. I cant see any real disadvantages besides maybe a little higher electric bill from running at a lower voltage.
It does bother me that you have two separate buildings running off two separate transformers with this problem. It will be interesting to see if this corrects your problems.
Ha! That single detail tells me that the problem has nothing to do with the machines. Instead it is either a coincidence - that both (high-leg delta) transformers are showing similar faults, OR that the problem is coming down the line from the grid. The coincidence is not impossible if the two trannies are the same, installed at the same time, but I will bet on at least some of the fault coming in from outside. But new Y-connection transformers are going to help handle some of the external problems.It does bother me that you have two separate buildings running off two separate transformers with this problem. It will be interesting to see if this corrects your problems.
Yes, it will cost you (at least to get every machine checked out for correct supply voltage), and yes, you may have to really lean on the sparks to get it done, but down the track you will be happy with your decision. Betcha!
I can't see your power bill going up as a result - except that you might get greater utilisation out of your machines. You might welcome that expense. :-)
Remember Admiral David Farragut!
Cheers
Wizard - I agree with your comments about the electrician i am using but the reason i am using him is because i know for a fact he is the most knowledgable electrician in our area when it comes to machinery and factory wiring. I have used him many times over the years and almost every factory in our local area uses him exclusively for this reason.
I am switching from 240VAC 3-phase high leg delta to 208VAC 3-phase wye. Right now we have our machine transformer taps set to lower the incoming voltage being fed to the machine controls to around 200~210V since the 240V is to high. So by changing to 208V we will have to switch our taps around but it should cause no problems. If one or two machines arent happy on the lower voltage i could easily install a buck boost tx for that particular machine. I dont expect to have any issues but murphys law im sure will come into play.
I guess the reason i thought the utility bill might change a little is from running lower voltage which in my mind means you need more amp draw to make the same amount of watts at the motors. More amp draw means slightly higher temps and less efficiency doesnt it? Maybe its a small enough amount to not really matter.
Rcaffin - That is the main reason i have chosen to switch our power supply. Im hoping there is a problem with the current transformers and putting new transformers in place will eliminate that possibility. I could have just had them replaced with the same high leg delta setup that we have now but
1st we have no need for the high leg,
2nd its not likely but is possible the high leg is causing problems,
3rd unless i could prove that the current transformers are faulty i doubt the city would replace them just to see what happens.
So why not. If this doesnt solve anything at least i know the transformers arent the problem and i need to look elsewhere.
Reply with Quote
