277/480V 4 wire Wye vs 240/480V 4 wire Delta service for Bitcoin mining

[skylark_cash]

Hello,

I'm located in Missouri and I'm in the process of upgrading my bitcoin mine to get about 300 kilowatt of power.
Need some help with figuring out what's the best option for me.
My cooperative power company give me two three phase transformer options.

Option 1. 277/480V 4 wire wye
Option 2. 240/480V 4 wire Delta

Option 1 will require a second dry type transformer to go from 277/480V to 240/415V Wye so will be a bit expensive.
Option 2 will not need a second transformer, since I can get 240volts from between line and neutral. This option seems too good to be true. Is there a catch here? Am i missing something ? This is a high leg delta system and I wonder if there are some inherent downsides to it, since most miners seems to prefer wye systems.

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[NotFuzzyWarm]

Um a simple search for high leg delta turns up https://en.wikipedia.org/wiki/High-leg_delta which explains it all...

Is not a matter of preference, high-leg systems are not really used anymore as the setup was always a compromise. In the US for several decades now straight 3-phase wye is preferred but as you said that requires as step down xmfr because most miner PSU's top at 250VAC -- feeding them 277 is out of the question.

[wndsnb]

Is there an option of bringing in higher voltage? 300KW might not be enough for the power company to give you that option, but I think if you have the power company deliver the higher transmission line voltage and use your own stepdown transformer you can get better rates, and you can decide exactly what configuration and voltage you want. Could also set you up for easier expansion in the future.

[skylark_cash]

@notfuzzyWarm thanks for your reply. I realize the 240/480V 4 wire Delta option is a high-leg delta setup. But this allows me to get 240 volt line to neutral voltage without needing to step down, so it seems like a good option to me. Why is it that people avoid these high-leg delta option? You mentioned that this is a compromise, but i'm trying to understand what exactly is the problem with this options. Is it harder to load balance? is it harder to find breaker panels or is it something else....

[skylark_cash]

@notfuzzyWarm thanks for your reply. I realize the 240/480V 4 wire Delta option is a high-leg delta setup. But this allows me to get 240 volt line to neutral voltage without needing to step down, so it seems like a good option to me. Why is it that people avoid these high-leg delta option? You mentioned that this is a compromise, but i'm trying to understand what exactly is the problem with this options. Is it harder to load balance? is it harder to find breaker panels or is it something else....

I have overhead cables coming right by my property  at 7200 volts. Unfortunately my power company only offers those 2 options for step down oil-filled transformers. They would not let me buy a 415Y/240V step down, since they say they will have to maintain the transformer and they do not want non standard equipment.

[wndsnb]

Yeah, in the case I was describing they would deliver the 7200V and you would be responsible for any equipment after that including your own transformer. Just the same as if you went with the 480V/277 and had your own transformer to step it down to 240. I've gone through the published rates for some areas in upstate NY, and this option is in their published rates, but I don't remember if 300KW was enough to qualify for the rate tier.

[NotFuzzyWarm]

Why is it that people avoid these high-leg delta option? You mentioned that this is a compromise, but i'm trying to understand what exactly is the problem with this options. Is it harder to load balance? is it harder to find breaker panels or is it something else....

That Wikipedia link explains it all.

The 'problem' comes when the 120V single-phase portions are used for lighting and other 120v things-  you need to make sure that every 3rd opening in the breaker panel is NOT used as it is the high-leg and will be around 134v vs 120v when referenced to the neutral. Beyond that the addition of 120v loads unbalances the 3-phase loads because the wild leg only supplies the 3rd phase.

Considering you will be mainly running 240v loads using 2-pole breakers everything automatically balances out. Just make sure you never plug a 1-pole breaker into the wild leg slots as it will not be 120v.

[skylark_cash]

Thank you, that really helps. As long as my electrician can stay clear of using the high leg by avoiding every third breaker, this 480/240 delta transformer should work.

[du5tin]

Ideally if a person could get a 240V/415V Wye setup that would be the best. Single pole breakers for each miner should be cheaper than 2-pole breakers so you get more capacity in a panel. I do not think that is a standard service size in North America though.

For a huge facility I would think the best is to go for a 347/600V wye service if it’s available. Then use step down transformers down to 120/208V for individual racks or buildings as it makes sense. More expense up front but might allow for smaller wire and breaker sizes running feeds to each subsection of the mine.

Interesting discussion! I am a ticketed electrician in Canada and have been considering how best to setup a mine from an electrical perspective.

[skylark_cash]

I think my best option is to get 480Y/277V and step it down to 415Y/240V.
However when i look online i do not find transformers that can do this. Most of the available transformers have a delta primary for a 415Y/240V secondary.

Does a 480Y/277V to 415Y/240 transformer exist? Has anyone done this before?

[NotFuzzyWarm]

Primary side of most transformers is delta and is connected directly to the incoming power so that is fine. It is the secondary side that we care about and prefer to be wye.

You will have 3 hot legs and chassis ground feeding the xmfr, a neutral is not used on the primary. The secondary wye side is where the neutral is created.

[du5tin]

Not fuzzy warm is correct. The input side of a transformer does not need a neutral, just three hot wires from different phases. On the output one side of each winding is grounded to create the neutral (wye). Your electrician will know how to hook it all up. If memory serves transformers can be field wired delta or wye at the time of installation. If you get the right voltages in/out you should be good. This is something I highly recommend getting an electrician to wire up for you.