WYE X WYE Transformer

[Tunneldigger]

New here, son is a electrician, but I am a farmer / plant maintenance. My other son is a farmer as well.
My electrician son doesn't know and I am having a electrician do the work. I do want to understand whats going on.
My son is putting up a Schivers dryer system all 480. Control voltage will be 120.
The power company says to go to 208 3 phase for the shop and the single phase circuits I need a Wye x Wye transformer. They say that they don't have Delta. I can find Delta x Wye transformers all day long but the Wye x Wye is problematic. He just wants 480 for bin stuff and 208/120 for control and shop usage.
Thanks for any help in understanding this!

 

[infinity]

We'll allow this question since there is an electrician doing the work.

Sounds like there is a 3Ø, 208Y/120 volt service and you also need 480? Why do you think that you need a Wye-Wye transformer? A 3Ø, 208 volt Wye-Delta would give you a 3Ø, 480 volt, 3-wire Delta output. A 208 volt Delta-Wye would give you a a 3Ø, 480Y/277 volt output.

 

[Tunneldigger]

The power company says that is what is needed. I am just trying to understand. I was talking to a vendor about the transformer and he said the only time he has ever seen a Wye by Wye is in a feedback application. Something like a private net metering solar or wind application. This project is just starting. I have a pretty good grasp on plant maintenance type stuff and work with our plant electrician. He doesn't know why they want this.
The power company guy is gone this week and my contractor is busy too.

 

[Tunneldigger]

I guess I should also say it is a 480 service and the step down transformer is after meter so that is ours. It looks like a 45 kva is big enough for the shop and 15kva for control voltage. The shop is 220 feet from the main panel so to keep voltage up at shop we want use 480.

 

[infinity]

I guess I should also say it is a 480 service and the step down transformer is after meter so that is ours. It looks like a 45 kva is big enough for the shop and 15kva for control voltage. The shop is 220 feet from the main panel so to keep voltage up at shop we want use 480.

So you have a 480 volt service, what type? Is it a 480Y/277 volt Wye service?

 

[Tunneldigger]

He is going to get a new 480 service and it is going to be Wye from the power company. I think on their end that is the only transformer they have. If we want something different it will be '25 when they can get it. It is a rural electric coop. My electrician is busy and he is the backup electrician at the plant where I work. I have been his "helper" more than once so he is my guy. He said if I got everything he could get there faster.

 

[kwired]

He is going to get a new 480 service and it is going to be Wye from the power company. I think on their end that is the only transformer they have. If we want something different it will be '25 when they can get it. It is a rural electric coop. My electrician is busy and he is the backup electrician at the plant where I work. I have been his "helper" more than once so he is my guy. He said if I got everything he could get there faster.

Just because the supply side is from a wye secondary doesn't mean you must use a wye primary for your step down.

A delta-wye transformer will do what you want just fine.

 

[infinity]

He is going to get a new 480 service and it is going to be Wye from the power company

A 480 volt Wye service is very common. You can use a standard Delta-Wye transformer to create the 208Y/120 volt system. Only thing left is the properly calculate what size transformer you'll need for the 208 and/or 120 volt loads.

 

[Strathead]

To summarize, forget about everything beyond your meter first. You state you currently have a 480v service and regardless of what you currently have the power company will be providing you with a 480/277 WYE system for the new. Additional concerns for this would still be, was the original system 480/277 Wye or 480 delta. If Wye no additional concerns. If Delta, some investigation and work may need to be done to ensure balanced load across the 3 phases when you finalize you new installation.

That done, you will be running 480 volts with the neutral to the shop. You said the equipment is 480 volts, so you will be putting a 480 volt panel in the shop. From there, you will not need a transformer for the dryer system, it looks like you think you do. You will want a step down transformer to get your 120 for control, but I assume you also have lights receptacles etc. If so you now have two options, if you NEVER expect any need for 208/120 volt three phase equipment, then just install a 25KVA 120/240 single phase transformer and panel for all 120 loads. If you you MAY need 3 phase in the future then I suggest at least a 30KVA transformer. The up front cost isn't enough more to warrant saving the money.

 

[kwired]

To summarize, forget about everything beyond your meter first. You state you currently have a 480v service and regardless of what you currently have the power company will be providing you with a 480/277 WYE system for the new. Additional concerns for this would still be, was the original system 480/277 Wye or 480 delta. If Wye no additional concerns. If Delta, some investigation and work may need to be done to ensure balanced load across the 3 phases when you finalize you new installation.

That done, you will be running 480 volts with the neutral to the shop. You said the equipment is 480 volts, so you will be putting a 480 volt panel in the shop. From there, you will not need a transformer for the dryer system, it looks like you think you do. You will want a step down transformer to get your 120 for control, but I assume you also have lights receptacles etc. If so you now have two options, if you NEVER expect any need for 208/120 volt three phase equipment, then just install a 25KVA 120/240 single phase transformer and panel for all 120 loads. If you you MAY need 3 phase in the future then I suggest at least a 30KVA transformer. The up front cost isn't enough more to warrant saving the money.

I took it as they added new equipment that needs or at least prefer 480 volts. I am familiar with the Shivvers drying systems he mentioned, he probably has a couple rather large drying fans and then a few associated auger motors and other motors for handling the grain. All which could likely be run @ 208-240 as well but 480 tends to be preferred. When they ordered the system it likely was ordered with motor starters and overloads sized for use @ 480 volts, almost everything else would have remained the same.

Around here most people in this situation likely will keep their existing service that supplies the shop, usually 120/240 single phase and subscribe to a second service supplying the 480/277. But there may be some POCO's that only want to supply you with one service and that is possibly his situation here?

I do agree that if shop already has single phase to it then probably just supply it from a single phase transformer, if there is no need or desire to add any three phase loads to it in the future. Keeping in mind this drying system will only be in peak demand during harvest time and will sit idle most the rest of the year. If this is a setup that goes on a storage bin then you still may have some "crop maintenance load" at times when running air through the bin. But you will have that load in any storage bins you are using anyway.

 

[Tunneldigger]

The service is going to be 480/277 Wye with a neutral. This will be at the bins. Then run a 480 line 220 feet away to a 45kva step down transformer to 208/120. Also want a 15 kva at main panel for 120 volt receptacles. Only need single phase at shop to run 120 receptacles, 220 volt welder, and air compressor. The shop currently is single phase and no plans to change it. The good/bad thing with the shop is it needs new feed replaced no matter what because of bad neutral. He has funky voltage and has only ran lighting and engine heaters since it went bad in December. It has hobbled all welding and air compressor use. He just bought the farm and there has been questionable craftsmanship on everything electric included. Thank you for all the replies!

 

[infinity]

The service is going to be 480/277 Wye with a neutral. This will be at the bins. Then run a 480 line 220 feet away to a 45kva step down transformer to 208/120. Also want a 15 kva at main panel for 120 volt receptacles.

So this is a pretty standard setup where you'll just need to provide step down transformers to get the 208 and 120 voltages. Circling back to your original question in the thread title a Wye/Wye transformer is not required for anything that you've described.

 

[zbang]

The shop currently is single phase and no plans to change it. The good/bad thing with the shop is it needs new feed replaced no matter what because of bad neutral.

If you have to run a new feed, make it 3-phase anyway even if the shop panels are single; the additional cost won't be much and it opens up many possibilities for shop equipment.

 

[wwhitney]

The power company says to go to 208 3 phase for the shop and the single phase circuits I need a Wye x Wye transformer.

I'm thinking the power company employee you spoke with is used to power company transformer specifications, which may well be wye-wye. On the customer side of the meter, I gather delta-wye is used instead.

Cheers, Wayne

 

[synchro]

I think that some confusion may

I'm thinking the power company employee you spoke with is used to power company transformer specifications, which may well be wye-wye. On the customer side of the meter, I gather delta-wye is used instead.

Cheers, Wayne

Yes, I was thinking along the same lines. The power company may want their own transformer to be wye-wye, such as from 12.5/7.2 kV to 480/277V, because wye-wye transfomers would be less susceptible to "ferroresonance", particularly if there are long distribution lines and especially when underground.

And so as a customer you just need to know that they will be providing a 4-wire 480/277V service, and a delta-wye on the customer side would be totally appropriate.

 

[wwhitney]

And so as a customer you just need to know that they will be providing a 4-wire 480/277V service, and a delta-wye on the customer side would be totally appropriate.

Beyond market availability, any particular reason for the customer to prefer delta-wye over wye-wye?

Cheers, Wayne

 

[synchro]

Beyond market availability, any particular reason for the customer to prefer delta-wye over wye-wye?

Cheers, Wayne

To have stable L-N voltages under unbalanced L-N loads, the center point of the wye primary would need to be connected to a neutral from the POCO. Triplen harmonics and common-mode noise, spikes, interference will pass through a wye-wye (at least within its bandwiidth}, but subastantially less so with a delta-wye. Some of this is also advantageous to the POCO and other customers on the same POCO feed. The 30° phase shift of a delta-wye is irrelevant unless there is a large customer getting multiple feeds into main-tie-main arrangements, for example.
Of course, a delta-wye will not need the neutral of a 4-wire feeder like a wye-wye, which could reduce costs epecially if the feeder is long. Others could chip in as well.