stepping down 3Ph 600v to 3ph 240v

so check this out. I live in a place where hydro rates are locked at 0.11$ per kWh (that’s what I had). I was shelling out 2500$ monthly for power with a 130amp single phase setup at home. Recently, I found out there’s actually 3-phase power available at the street. I’m thinking about bringing in 600v to my workshop for my tools. If I were to install a 400amp 600v feed in my shop and then step the voltage down to 240v 3-phase, continuing to use 130amps at 240V, would my monthly bill (assuming no other loads) still be around 2500$? Or would the amp draw theoretically be lower on the 600V side, since I’d be using half the amps to get to 240V? If my math is correct. I’ve seen 3-phase 600v 80 amp breakers power a step-down transformer that supports over 130 amps at 208v... what do you all think? I was also considering a grid tie setup, but our grid limits me to 18k kWh annually... I used that much in just one month.

Power is volts times amps. 130A 240V makes 31.2KW and at 208V that means 150 amps. From 600V it's 52 amps. Any step-down transformer stage will lose a bit of power. If your 600V three-phase is significantly cheaper than your single phase (probably split phase 240?) you could probably come out ahead. When I ran a small DC, we switched into a "small industrial" rate schedule when we crossed 100KW draw on a 3-phase 400V feed and it dropped the average rate from 8.9c to 6.5c per KWh. Since power is billed by KWh, raising your voltage to drop the current won't necessarily save on your bill. It'll depend on if they bill 600V 3ph at a lower rate than residential single phase.

Ah yes. Thanks for clearing the math up. I know that formula well. I used it lots... why I could not wrap my head around that answer is beyond me lol.  Makes sense all the way thanks  once more.

NotFuzzyWarm and some others who know power could probably chip in with better specifics. My knowledge is largely academic.

No, you pretty much nailed it. The efficiency of any decent large power transformer ranges from at least 97% and for premium ones is over 99%. That leaves only the rate plan as a variable when it comes to incoming voltage & power. Oh, and of course the 1-time cost of the transformer if you have to pay for it If you are the one supplying the transformer this is certainly a case for spending more to get a premium high-efficiency one vs the cheapest you can get. Considering that all of the power will be going through it, when pulling say 100kva through it every 1% difference is 1kva saved or lost. Using a 30 day month that = 720kWh/month so that cost adds up fast.

Great stuff! Ya 1% adds up what you put it that way.

Note I gave you some merits for following up keep posting and you will leave 'newbie' status.

Nice thanks. Do you guys think oil cool step-down would be worth it? I know the transformer on the pole did not like me when it boiled its oil at -30. Mindyou it was a 30 year old unit. But this new one humms just as bad when I put 140amps to het 247 lol

Are you talking about the transformer off the feeder circuit? Air cooled high voltage transformers are not common. Low voltage like 600 to 230 are almost all air cooled. Humming is normal (cool fact, since the the cycle breaks zero twice the sound you hear is actually 120hz) if it makes a buzz thats laminated core coming apart.

You normally only see oil cooled transformers on the Utility side of the power feed where the *possible* fire hazard remains outside of the building and the transformer has to be sealed against the elements as well as handling the multi-kv feed from the Utility. The user side of power distribution is almost exclusively air-cooled dry transformers. Ja they can buzz and definitely get rather hot but that is just the nature of the beasties,

Ahh ya that makes sense! Let me tell you the oil on the pole was boilling pretty good haha.  When I called the utility I said make sure the boys bring a transformer former the dispatcher said how do you know what's the transformer...  Well the sizzling popping boiling sound inside the canisters telling me that's probably what's going on. The buzzing makes sense. Same with the hum! Love those little hidden facts!  I'm a refrigeration mechanic so I sit near Transformers all the time in mechanical rooms The things that go on beside you and you have no idea

Across one phase. Across three phase 130A at 240V 3phase 130 x 240 x 1.73 = 53,976 W

54kw... I forgot about the 1.73 rule. That said it gives .73  more available draw on the third leg. But the idea is will the utility see 130amp draw or will they see the lesser draw of the 600v. In ontario residential and commercial rates are the same unless you use 1mw or 0.5mw.

[/quote] 54kw... I forgot about the 1.73 rule. That said it gives .73  more available draw on the third leg. But the idea is will the utility see 130amp draw or will they see the lesser draw of the 600v. In ontario residential and commercial rates are the same unless you use 1mw or 0.5mw. [/quote] Utility side would see the same (minuscule difference). Ideally you would have your load balanced across the phases. Bringing in 600 and stepping it down economics depend on many factors. The transformer cost and 3ph 600v panels/load boards and breakers are considerably more expensive. But have a lower copper cost so long runs could be a factor.  If your not getting a break on the kwh cost it may be better to bring it in at 230 and use commodity gear. You can also find 230v switchgear pretty cheap used / craigslist /ebay.

Okay but he specified 130A on 240V single phase, which means he was drawing 31.2KW total. Switching to 3ph, let's say it steps down to 208V l-l, the equipment will still be asking for 31.2KW which means 150 amps total, 50 amps per leg. At the 600V side the total draw is around 52 amps (plus transformer losses), around 17 amps per leg. The 1.73 rule doesn't make power magically appear, just changes how it gets there.