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Author Topic: Delta vs WYE 3 Phase Electrical Service  (Read 1572 times)
Hockeybum
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May 16, 2017, 05:01:52 PM
 #1

I've got a question regarding Delta vs WYE 3 Phase service.  

If I understand WYE correctly with 200amp 120/208 service, that would give me 208V x 200A x 1.732 = ~72kW available power.  Each hot leg would be 120V x 200A = 24kW x3 legs = 72kW.

Can someone tell me how that equation works out for Delta service?  I have 240 volts between each of the phases, 120 volts to ground on 2 legs, and 208 volts to ground on 1 leg.  Is the equation 120V x 200A x 2 + 208V x 200A? That equals 48kW + 41.6kW = 89.6kW when adding the phases separately?  How does that translate to 3 phases when trying to calculate total kW?

Unfortunately the building where I'm at has Delta 3 Phase so I'm trying to understand how much power is available with that service.

I appreciate any feedback and/or corrections of my calculations.
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NotFuzzyWarm
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May 16, 2017, 06:42:41 PM
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Power is the same regardless of delta or Wye.
From the end user view the main difference is having one wild leg that is only a 220v power feed and a neutral at the center of one winding for 110v from it to the other 2 legs. Yes you have three phase power but the loading is very unbalanced whereas a wye will give 220 across each of the 3 legs and/or 110v from any leg to the center-point neutral.

Assuming a balance load 3-phase equation is V*average current of the 3 legs (or just pick the highest current one)*1.73= Watts
ref https://en.wikipedia.org/wiki/Three-phase_electric_power

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May 16, 2017, 06:55:22 PM
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Power is the same regardless of delta or Wye.
From the end user view the main difference is having one wild leg that is both a power feed and a neutral for 110v from it to the other 2 legs and there is only 1x 220v tap whereas a wye will give 220 across each of the 3 legs and/or 110v from any leg to the center-point neutral.

3-phase equation is V*total A*1.73= Watts
ref https://en.wikipedia.org/wiki/Three-phase_electric_power

Why is there two differences? Just trying to get my head around the reasoning between Delta and Wye. Both are three phase, is there an advantage to using Delta over WYE?

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May 16, 2017, 07:05:23 PM
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Blame Thomas Edison.... He is the one that came up with the delta configuration to compete against Tesla/Westinghouse and their balanced 3-phase power systems.

Part of the feud between him and Tesla involved Tesla figuring out that 3-phase motors are more smaller and more efficient than single-phase motors and that requires 3 hot legs referenced to a neutral/ground. Once he was forced to start working with AC, Edison based his power distribution on the notion that most users would be using single-phase, 110v for lighting and the (single) 220v for high watt loads.

For most small commercial and office loads Delta makes sense because you don't need a transformer to get 110v services and 480v (wye) service is typically reserved for companies wanting several hundred kw of power.

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May 16, 2017, 07:10:06 PM
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Blame Thomas Edison.... He is the one that came up with the delta configuration to compete against Tesla/Westinghouse and their balanced 3-phase power systems.

Part of the feud between him and Tesla involved Tesla figuring out that 3-phase motors are more smaller and more efficient than single-phase motors and that requires 3 hot legs referenced to a neutral. Edison based his power distribution on the notion that most users would be using single-phase, 110v for lighting and the (single) 220v for high watt loads.

For most small commercial and office loads Delta makes sense because you don't need a transformer to get 110v services and 480v (wye) service is typically reserved for companies wanting several hundred kw of power.
Ah, that makes, sense. Three phase motors in industry are more efficient than single phase. Thanks for breaking it down for me.

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Hockeybum
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May 16, 2017, 07:22:39 PM
 #6

Thank you very much for the feedback, really appreciate it.  It makes sense that there is Delta service there, it's a light industrial building with office space.  I'm trying to get 120/208 800 amp service there so that I can run a few more miners, but with permitting and city approval that will take probably until the end of the year.  Tesla is the man, too bad Edison tried so hard to discredit him.
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May 16, 2017, 08:42:43 PM
 #7

You may have difficulty obtaining/upgrading center-tapped delta service. Electric utilities don't like them because they are a source of asymmetry in the grid. Look at the transformer diagram in

https://en.wikipedia.org/wiki/High-leg_delta

from the point of view of the utility. If you pull 200A each from the low legs (SA & SC on the diagram) than means 48kW of power on the a single primary transformer winding (PA & PC) but zero power on the primary windings PA-PB and PB-PC. This is inefficient use of the capital spent on the transformer(s).

So they will push you to either:

1) use very little (about 5%-10%) power on the high-leg. They will then use two transformers, one much smaller than the other.

2a) buy equal amounts of power through each of the transformer windings. That would mean the amperage on the high-leg will be different than on the low-legs.

2b) use symmetric hookup with all leg voltages equal.

The exact rules in the USA are state-dependent and utility-tariff-dependent. Most likely they will flatly refuse upgrade if they sense that you don't understand the basic trigonometry required to balance the load. Then you will be forced to get not only certified electrician but "engineering supervision" before they agree to upgrade the asymmetric service.

It may be worthwhile (moneywise) for you to understand the equations before you talk to the utility people. Avoid burning bridges by asking stupid question when talking with them. They can legally refuse or stall your install when hooking you up would significantly unbalance their grid.


Please comment, critique, criticize or ridicule BIP 2112: https://bitcointalk.org/index.php?topic=54382.0
Long-term mining prognosis: https://bitcointalk.org/index.php?topic=91101.0
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May 16, 2017, 10:14:45 PM
 #8

My shop was wired for 200A 3phase wye, which was one of the deciding factors on whether to lease it or not. I set up all my miners on three shelves, each with a sub-panel pulling from two legs so I can pull 120V or 208V with a single- or double-pole breaker. At the junction box where the legs drop to the subpanels I have current meters installed so I can check loads at a glance, handy for knowing where to install new gear to keep things balanced. All the miners are run on 208V because, well, it's better.

The pole has three transformers wired on a common neutral, almost trivial to handle when I upgraded to 400A service. The new feed from the pole and the new distribution panel weren't cheap but the whole thing took only one day to make the change.

Delta would have just made everything way more difficult to wrangle. If you're already doing the work of swapping up to 800A, I'd definitely see how difficult it'd be to rewire the existing setup for wye.

Hockeybum
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May 17, 2017, 01:25:03 PM
 #9

The existing city transformers are at capacity so they have to install new transformers on their end to service the building if I upgrade to 800 amp service.  I'm hoping that they can put in wye service at this point and then I can rewire the building internally.  My cost to the city for 800 amp service is $21,000.  After getting an electrical engineer and electrician for connection and distribution I'm probably looking at $75,000 for the project.
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May 17, 2017, 01:55:31 PM
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Dang, that's a tall bill. I'm in a rural co-op; for my 400A upgrade they swapped the transformers at no charge and I did the rest. Material cost for the upgrade, including adding 200A pulls and panels to the hosting shelves, was under $5000. Mostly the 3-phase distro panel and 1300 feet of 250kcmil aluminum. Fortunately the pipe from the pole was way overspec for the 200A pull or retrenching would have doubled that budget.

$75K, that's a lot of dollars. Have fun.

NotFuzzyWarm
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May 17, 2017, 02:08:29 PM
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That sounds like a reasonable ball park price.

When we moved SLI to our new facility we upgraded the building from 150kw 208v wye up to 500kw 480V wye. Consumers Energy covered cost of their transformer and we paid for everything else. Including trenching from pad to building for bigger cables, the main and 3 smaller service panels, a 800A 480-208 xmfr for systems that don't like 480 (and a disconnect panel from that) and a couple smaller distribution xmfrs for the offices, bus ducts, etc., I think it ran us a bit over $170k for the upgrade.

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sidehack
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May 17, 2017, 02:10:02 PM
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Okay well, now I feel like I got a discount.

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May 17, 2017, 02:18:15 PM
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Okay well, now I feel like I got a discount.
Well the fact you did most of the work yourself certainly helped on price Wink
Also, we spec'd no aluminum wire - Cu only - plus panels/disconnects rated to 600VAC are substantially more pricey than 300V gear.

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NotFuzzyWarm
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May 17, 2017, 08:53:58 PM
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You may have difficulty obtaining/upgrading center-tapped delta service. Electric utilities don't like them because they are a source of asymmetry in the grid. Look at the transformer diagram in

https://en.wikipedia.org/wiki/High-leg_delta <snip>
Thanks! I was looking for a diagram like that to better explain the Delta connection.
Bookmarked.

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May 17, 2017, 10:37:56 PM
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Thanks! I was looking for a diagram like that to better explain the Delta connection.
Bookmarked.
Well, enjoy your HTTP bookmark.

I just wanted to provide additional, mental bookmark, for those that are still confused. It is better to not call that weird asymmetric connection with single word "delta". It is properly called "high-leg delta" or "four-wire delta". The unqualified "delta" is a three-wire, no-neutral, type of service hookup. The eventual 4th conductor is just protective grounding, explicitly prohibited from carrying any significant current under normal operating conditions. In many high-power installation the "ground" is the actual ground of the Earth, there isn't any 4th conductor.

NotFuzzyWarm mentioned the historical origin of this weird service in the USA. The legacy of it still stays in the intentional and accidental misinformation in many sources on the web and even in many lower-level textbooks and training materials.

It looks like the original poster Hockeybum had already budgeted for electrical engineer's consulting expenses. For many people (not familiar with peculiarities of the North American grid) this would be an unnecessary expense, sort of a tax on lack of knowledge of trigonometry or calculus. Rest of the world wouldn't have to concern themselves with strangeness like "split-phase", "high-leg delta" or "corner-grounded delta". It seems like sidehack had avoided this tax by intentionally opting for the safest choice of "wye"  (known as "star" throughout the rest of the world).

For the benefit of future readers who want to avoid additional EE consulting expenses I have the following advice: search for a electrician who is at least familiar with things that are outside of "the code"/NEC . The good thing to ask for is a https://en.wikipedia.org/wiki/Zigzag_transformer or https://en.wikipedia.org/wiki/Scott-T_transformer
even if you don't plan on getting one. It will probably mark you as an "educated buyer" not as somebody who is relatively easy to bamboozle with jargon to buy both belt and suspenders to match their new Bermuda shorts.

Please comment, critique, criticize or ridicule BIP 2112: https://bitcointalk.org/index.php?topic=54382.0
Long-term mining prognosis: https://bitcointalk.org/index.php?topic=91101.0
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May 17, 2017, 10:43:54 PM
 #16

(I also have a degree in EE, plus background in construction and residential electric, and the guys at the supply house answered a few questions)

But yeah, high-leg delta looks to be pretty easy to screw up especially as far as balance goes, and then there's the risk of accidentally 208ing your 120V circuits if you grab the wrong leg.

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May 18, 2017, 01:55:46 AM
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Ja to both ^^

It kinda sounds like the current setup the OP has is pulling power from the shared low voltage parts of the local grid. (lower sets of wire on poles) which is often fed by several smaller HV-LV transformers along the run. That is where I've usually found the high-leg delta 3-phase.

It occurred to me that since the OP sounds like he is upgrading the entire building service, is that including replacing the utilities service transformer(s)? Be they 3x pole pigs or a pad mount serving only his location, if so the utility should be able to solve the whole mess by installing the typical Delta (utility side) to wye (building side) transformer. If the utility has 3-phase on the high voltage tops of the poles to feed the dedicated service, should work.

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May 19, 2017, 03:56:06 AM
 #18

I forgot to mention that I am also the building owner, so upgrading makes sense even without crypto mining.  Light industrial buildings in my city are at a premium because of the lower power rates compared to PG&E; lots of machine shops on my block.  I'm hoping that the city will provide wye service from their side when they perform the upgrade (city owns the utility).  I'm sure it will be 5-6 months before permitting is complete, so it will be a long process.  In the mean time I'll have (2) 3 phase 60 amp dedicated outlets installed next week to run 24 S9's.  The electrician mentioned something about a transformer probably to deal with the Delta service.  I'll have 1 18.7kW PDU per outlet and 12 PSU's driving 12 S9's.  I'm not sure if I can run more on there, but I think I could push it up to 14 per circuit.  Electricity isn't my forte, just trying to learn more about it.
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May 22, 2017, 02:44:36 AM
 #19

Honestly, it doesn't make sense to mine in CA.  I would take your 75k, buy miners with it and run them at a colo data center.

What is your effective power rate when considering demand charges ect?
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May 22, 2017, 04:17:31 PM
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Thank you for all the replies and feedback so far.

The electrical upgrade on the building was an idea prior to me getting involved in bitcoin, it makes financial sense as an investment for the long-term marketability of the building.  Also, I'm not using the entire building in my main business so I do have space for racks, shelves or even purpose-built data rooms.  The one thing I don't have now is power, just 200 amp 3 phase 208 at the moment.

I do not know the power factor that is to be taken into account so if someone wants to clarify that, please do.  Also, my numbers below do not take into account ventilation and/or cooling costs, just the bitcoin miners themselves.

The meter charge is $66.17
Demand is              $  8.00 per kW
Energy is                $0.10629 per kWh

An an example, running 1 Antminer S9 13.5 TH/s for 1 month.  1.323 kW x 24 h x 30 d = ~953 kWh per month x .10629 = $101.29 + $10.58 demand + $66.17 meter = $178.04 = eff rate of $0.1868
another example, running 100 Antminer S9's 13.5 TH/s 1 month.  1.323 kW x 24 h x 30 d x 100 = 95,256 kWh per month x .10629 = $10,125 power + $1,058 demand + 66.17 = $11,249.17 / 95,256 kWh = eff rate of $0.11809

I know I am paying more per kW than a lot of other places, but for California my rates are really low.  I do have the benefit of close proximity and full control of the miners, also I'm not paying rent for the miners as well because the space is already there.  If anyone has any comments or corrections on my calculations please let me know.






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