Three phase in property, single phase services w/ ESS

[jkahn299]

Hello all... I've got a project that is absolutely absurd... We're doing a 4MWh ESS system for a 200k sqft build in Colorado. The project is spec'd with (2) 1200A utility services (single phase). We also have the ESS system which we can set up as single or three phase. We're considering doing a three phase system for the property, so the question is could you use solar and batteries for three phase power and then use two separate incoming service feeds w 240-208 transformers to create 3 phase power for a property, even though the utility feeds are single phase.

The concern is that with two 1200A services you'd have two hot legs at 600A from each service, combining them would give two 600A legs and a 1200A leg, or unbalanced three phase. Am I thinking about this correct, and would that work within the property even though it's unbalanced? Let me know what y'all think!

 

[tom baker]

Can you explain what an ESS is, how it works and why it is used for this application?

 

[jkahn299]

Can you explain what an ESS is, how it works and why it is used for this application?

ESS is Energy Storage System (batteries). We can stack inverters and back up all three phases evenly for a house with a three phase service, or just back up a single phase. Basically we're able to supply the MDP w/ balanced three phase power in the case of a grid outage, or if time of use settings are on. Whether it makes sense to do a three phase service to the residence or not, the ESS will be able to back it up. The question is really in regards to creating the three phase service from two 1200A single phase services if we want to use three phase in the residence.

 

[texie]

No on a number of levels. You can't magically make 3 phase with just a transformer. Also your service size description is not correct. Pardon the question, but are you really an engineer?

 

[jkahn299]

No on a number of levels. You can't magically make 3 phase with just a transformer. Also your service size description is not correct. Pardon the question, but are you really an engineer?

Yes I am haha, be nice though I am fresh out of school and working with non-engineers so if my language is incorrect I'd happily be corrected. Can you explain what is incorrect about having two 1200A services? This is a castle we're talking about... And I figured as much, I was just curious if anyone had seen a project where multiple single phase services had been combined to form a three phase system for the property, and if they had how, since as you said, it's not something a transformer could magically do. I know it's a little backwards but running three phase in the house would be ideal due to the insane usage and presence of large motors and the guy didn't pay to pull a three phase service.

 

[winnie]

If you have two single phase sources with a 120 degree phase angle between them, you could combine them with a transformer to create the full three phases. Unfortunately you won't have two sources with any defined relationship between them, you will have two _services_. The utility wouldn't have any obligation to provide specific phase angles, and you would need to carefully design any 'combiner' system to prevent one service from back feeding the other.

Your energy storage system could in theory provide the phase conversion, but now all power would be flowing through the energy storage system all the time.

The best approach IMHO is for the internal system to match the external, either by using single phase in the building or by getting the utility to provide 3 phase service.

Jon

 

[jkahn299]

If you have two single phase sources with a 120 degree phase angle between them, you could combine them with a transformer to create the full three phases. Unfortunately you won't have two sources with any defined relationship between them, you will have two _services_. The utility wouldn't have any obligation to provide specific phase angles, and you would need to carefully design any 'combiner' system to prevent one service from back feeding the other.

Your energy storage system could in theory provide the phase conversion, but now all power would be flowing through the energy storage system all the time.

The best approach IMHO is for the internal system to match the external, either by using single phase in the building or by getting the utility to provide 3 phase service.

Jon

Thanks Jon! This is right along with what I was thinking. We could do three phase if we ran everything through the inverters and used them to provide the phase conversion. I was just curious if there would be a way to do it prior to the inverters, and without knowing the relationship that seems like it would be quite difficult. I appreciate that answer!

 

[jkahn299]

No on a number of levels. You can't magically make 3 phase with just a transformer. Also your service size description is not correct. Pardon the question, but are you really an engineer?

OK I'm getting that this is impossible, which I figured it may be, and that's why I came on here. However, I'm still scratching my head as to why you said my service size descriptions were so wrong you thought I wasn't an engineer... Am I missing something? What is incorrect about having (2) 1200A Services?

 

[texie]

OK I'm getting that this is impossible, which I figured it may be, and that's why I came on here. However, I'm still scratching my head as to why you said my service size descriptions were so wrong you thought I wasn't an engineer... Am I missing something? What is incorrect about having (2) 1200A Services?

You said each leg is 600 amp. That is a 600 amp service, not 1200 amp.

 

[gar]

221005-1743 EDT

In our area it is extremely common to take two phases from a three phase source to two transformers to provide a three phase output even though there is three phase power available at the transformer input. Thus, only the cost of two transformers. If the three phase load increases in the future, then it may only the need the addition of another transformer.

.

 

[jkahn299]

You said each leg is 600 amp. That is a 600 amp service, not 1200 amp.

Oh I see the confusion... I didn't mean grabbing each leg of the 1200A service I meant splitting the service into (2) 600A feeds with 4 wires. That's where I was getting 4 wires each with 600A and the unbalanced power. Keep in mind this concept came from a guy with no electrical engineering background and sounded impossible to me from the get go but I wanted a better answer than just "that won't work." I appreciate you clearing that up for me.

 

[jkahn299]

221005-1743 EDT

In our area it is extremely common to take two phases from a three phase source to two transformers to provide a three phase output even though there is three phase power available at the transformer input. Thus, only the cost of two transformers. If the three phase load increases in the future, then it may only the need the addition of another transformer.

.

That's a cool set up. Too bad the utility wouldn't pull three-phase to our site!

 

[winnie]

One big question is how the calculated load compares to the ESS capacity, the utility capacity, and any local generation (PV).

The utility might not be interested in upgrading their infrastructure if they expect minimal consumption from the customer.

You have half a megawatt of utility service, but I bet that even a 200k square foot castle doesn't use nearly that much. (On the other hand, 100x the size of my house with 25x the electrical service...)

Jon

 

[texie]

That's a cool set up. Too bad the utility wouldn't pull three-phase to our site!

You need to do more study of 3 phase systems. The system Gar is referring to is very common in some areas but has limitations. For starters it is only available where the utility has at least 2 of the 3 phases available and the primary is Y. Also, you end up with a delta secondary with a center tap neutral. That means the secondary will have 1 leg at 208 volt to neutral which can't be used for 120 loads. This is known as 240/120 volt 3 phase 4 wire system. They have their place and are very economical for the utility to build but it has it's limitations.

 

[gar]

221005-1926 EDT

texie:

The limitations you suggest really don't exist. With two appropriate transformers all combinations of wye and delta are possible.

Play with drawing some various vectors and you will see what is possible.

.

 

[jaggedben]

The utility is seriously willing to give you two 1200A services but not three phase? How many times have you asked them?

 

[texie]

221005-1926 EDT

texie:

The limitations you suggest really don't exist. With two appropriate transformers all combinations of wye and delta are possible.

Play with drawing some various vectors and you will see what is possible.

.

I understand that. I'm talking about what is practical and considered commercially normal and NEC compliant.

 

[gar]

221005-2004 EDT

texie:

Any of those connections are practical and NEC compliant. Commercially available will depend upon the power company.

.

 

[texie]

221005-2004 EDT

texie:

Any of those connections are practical and NEC compliant. Commercially available will depend upon the power company.

.

OK, you know best. I'm just starting out and learning.

 

[tom baker]

You picked a challenging service to start with