3 phase service

Do you mean 2 high voltage wires or 2 transformers?
Three phase is possible with 2 transformers, but not with 2 high voltage lines.
Reply to
Jim Stewart
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One consideration that is not electrically oriented is if there is a house fire and there is no meter for the firefighters to pull for their safety, they will just stand by and watch the house burn.
Paul
Reply to
KD7HB
Open Delta. Only two transformers, and ONLY two high voltage lines to feed the TWO transformers. Pretty common all over.
Reply to
Cross-Slide
Three phase can be had off of two hi voltage primary wires. It is just that you have no choice but to go open delta on the lv.
John
Reply to
john
Yuck. You're right. But you do have to have a neutral referenced to the hv wires.
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What an ugly kludge. I'm surprised anyone would use such a thing.
Reply to
Jim Stewart
Slab type transformers aren't particularly difficult to locate outdoors or indoors.
An armor channel covers the HV side conductors downward along the side of the utility pole, as underground service is typical with pad xfmrs.
Various sizes of outdoor-duty types can be seen around commercial sites, and also mobile home parks and campgrounds.
In a wire mill environment where I worked years ago, the KV lines were run underground into the facility, and the switchgear, xfmrs and various cabinets were mounted on a reinforced overhead slab standing on beams. The 3-phase 460VAC circuits were branched out with buss systems.
Reply to
Wild_Bill
Yes, but typically the utility will only provide a pad mount if the user is not close enough for secondary service from a pole or existing pad mount.
Reply to
ATP
All the plants that I do maintenance in are old.... transformers all sit behind a chain link fence.
Now that I think about it most residential developments around here are fed underground with a nice neat little pad and transformer a couple of feet high and about 4 foot square. A commercial installation would be just a little bit bigger.
I'm surprised that the electric co. doesn't supply you the transformer for free if you use a minimum amount of power.
John
Reply to
John
Personal would be on the ground seems to me.
Small company ? - larger one ?
Building contractors put them in neighborhoods - have overages ? Cosmetic ?
Martin
> > john wrote: >> >> Karl Townsend wrote: >>> >>> >>>> Pete C. wrote: >>>>> >>>>> J>>>>>> >>>>>> >>>>>>> "The Kid" is putting in underground wiring to his outbuildings. For >>>>>>> now, power will come from the house to the shop. >>>>>>> >>>>>>> The shop sits twenty feet from a three phase line. future plans is to >>>>>>> install a three phase service to the shop, cut the ordinal transformer >>>>>>> out, and then feed one phase back to the house from the wiring being >>>>>>> installed now. >>>>>>> >>>>>>> OK, a one phase house service has two 110 legs on the same phase >>>>>>> opposite polarity to get 220 across the two hot wires, neutral is the >>>>>>> center tap. As I understand it you in effect get three 110 hot wires >>>>>>> 120 degrees apart in the phasing for three phase with the center tap >>>>>>> for neutral. >>>>>>> >>>>>>> So, can you run single phase 220 off this? Need any special provisions >>>>>>> installed now? He's putting in conduit - four wires - two hot, neutral >>>>>>> and ground. >>>>>> There are essentially 4 ways to wire a 3-phase 2xx Volt service. >>>>>> There is 240 V delta, and 208 V Wye service. 240 V delta is not what >>>>>> you want here. 208 Wye service will work, but if you hook the house >>>>>> to 2 of the 3-phase hots, you get 208 V on the appliances that expect >>>>>> 240. Check the air conditioners, etc. carefully for their ability to >>>>>> run off 208. >>>>>> >>>>>> Then, there are two variants of the above systems, you may not be able >>>>>> to get these installed by your local electric company. One is >>>>>> corner-grounded delta, that gives you 2 240 V hots, good for running machine >>>>>> tool motors, the advantage is you can use normal 2-pole electrical >>>>>> panels and 2-pule breakers. No 120 V in that service, so not suitable >>>>>> for the house. >>>>>> >>>>>> The last form is center-grounded delta. It gives you both a 3-phase >>>>>> service, as well as one phase that is grounded at the center-tap. So, >>>>>> those two hots and neutral look exactly like single-phase home service. >>>>>> There is a third leg to provide the 3rd phase. >>>>>> >>>>>> IF!! you can get your electric utility to provide this service, it >>>>>> probably is the best choice, as you get real 240 V single phase >>>>>> service PLUS 3-phase with only 5 wires (3 phases, neutral and ground). >>>>>> >>>>>> Jon >>>>> >>>>> That last one is also known as "wild leg" delta service since the third >>>>> phase is not at 120V relative to the ground/neutral, and that third >>>>> phase is normally color coded orange to identify it. It wouldn't be a >>>>> problem for the house, since that wild leg wouldn't be fed to the house, >>>>> but it has been known to cause confusion and blown up 120V stuff in many >>>>> installations. Another issue with this type of service is that some >>>>> three phase machines may want 120/208V Wye service with it's neutral to >>>>> phase voltage at 120V for all phases. >>>>> >>>>> Generally, if you ask the utility for three phase service, you will be >>>>> getting 120/208V Wye service unless you specifically ask for something >>>>> different. Expect a lot of questions if you ask for three phase service >>>>> and a lot more if you ask for anything but the common commercial >>>>> 120/208V Wye service. >>>>> >>>>> As noted, most appliances these days are 208/240V rated since 120/208V >>>>> service is very common in apartment buildings. Check everything to be >>>>> sure, but you're not likely to find much that isn't ok with 208V. >>>> >>>> >>>> The 240 volt systems were designed to save the power company from >>>> installing an extra pole transformer for 240 volt single phase service. >>>> >>>> With 208 single phase two pole transformers were needed, and if three >>>> phase were required you needed to install three transformers to obtain >>>> the star or wye configuration. By using the center-tapped transformer >>>> neutral transformer it eliminated a second transformer. If three phase >>>> was required it was necessary to add only one more transformer rather >>>> than two, except when higher power rating were required and a third >>>> transformer is used. That was the difference between open leg delta and >>>> a full delta secondary. A lot of people are confused by seeing only two >>>> high voltage primary wires and getting fed with three phase into their >>>> building but that is very common. >>>> >>>> >>>> John >>> >>> Guys, thanks for the discussion on types of three phase. Bit more to >>> this than I thought. he's talked with the power company and will get >>> FAR lower install cost if he provides and maintains the transformer. >>> We're, of course, looking for a used one. With all the different >>> primary voltages out there and now all the flavors of three phase, >>> this looks like a tuff task. >>> >>> Karl >>> >> >> Karl, >> >> Search for pole transformers. If its only the installation cost that is >> different I would go for the extra buck and let the power company own >> the transformer. If you happen to have one blow from lightning or some >> other problem it will be a lot faster if they come and replace it rather >> than you searching for a replacement. Also wait till you check on some >> of the prices of those pole pigs. Unless you are going to draw a lot of >> power you can run open delta with one 240 center tapped grounded and one >> 240 single phase unit. You only need two legs of the delta to get the >> three phase but you get a little less regulation and can only pull the >> wattage of the two transformers. Most smaller shops on three phase only >> get two pigs on the pole. >> >> John > > He's probably looking for a pad mount transformer, not a pole pig.
Reply to
Martin Eastburn
Ugly ? - add another transformer and you have true 100% power 3 phase.
With two - and that two gave you three phase and split 220 as well.
So it used the center tap on the right side If split 22O came from the house on the underground - and the three phase from the pad transformer, then only three secondary wires are used.
The Military and police/fire all use Three Phase. Delta-Delta.
The idea - overrate the transformer by at least 1/3 but normally 1/2. Then if or when worse comes to worse, and an input leg is lost, or a winding is lost (bullet...) the secondary can continue at ~66% e.g. 100% of wanted (due to overrate.) They could take a hit on the primary and secondary and still stay alive.
Martin
Reply to
Martin Eastburn
Meter on the pole or in the pad transformer - normally on the end and the sides hinge open. Nothing is hardwired by professionals.
Our big pad units had meters on then.
Martin
Reply to
Martin Eastburn

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