240 3ph ->480 Xfmr

[Open Neutral]

We're getting 3ph open delta from PG&E. We alas have a 480v 3ph 2 hp. pump in place 750ft down.

So I'm looking at 240->460 transformers. But most I see are wye on the LV side, delta on the 480. As far as I can see, the motor [http://www.franklin-electric.com/re...ModelNumber=234 325 94--S#model234-325-94--S] is 3-wire, so feeding that sole load with a delta leaves everything floating.

What are my options? Obvious would be a non-stock 240 delta-> 460 wye transformer. Others that the electrician & inspector will like...?

[Don't even ask about swapping the pump motor. $2K+ in labor to pull; & ~that to install a 208/240 one..plus buying it.]

 

[augie47]

You can use one that is wye on the low voltage side and ignore the LV neutral, , however, it will most likely be 208 rated on the LV side and not match your 240 system.
A 240 delta to 480 delta should be readily available.
If your HV side is delta, you can elect to ground one phase or use it as an ungrounded system.
There are specific Code rules for each.

 

[ptonsparky]

This is more of a thought than an answer.

No bigger than load is, can you set a pair of bucking transformers to drop your 240 to 208 then go with a standard 208 to 480.

We do not have three phase in our shop. We do have a single phase transformer we reverse feed to get 480 single phase. We then use a 480v VFD to operate those motors that will be running at 480v. Might be a relatively in expensive solution.

 

[ptonsparky]

Page 4 of Franklin's AIM manual suggests 2 - 2 kva single phase transformers set up in an open delta configuration as min size. Those should be a stock item in your area.

 

[kwired]

We're getting 3ph open delta from PG&E. We alas have a 480v 3ph 2 hp. pump in place 750ft down.

So I'm looking at 240->460 transformers. But most I see are wye on the LV side, delta on the 480. As far as I can see, the motor [http://www.franklin-electric.com/re...ModelNumber=234 325 94--S#model234-325-94--S] is 3-wire, so feeding that sole load with a delta leaves everything floating.

What are my options? Obvious would be a non-stock 240 delta-> 460 wye transformer. Others that the electrician & inspector will like...?

[Don't even ask about swapping the pump motor. $2K+ in labor to pull; & ~that to install a 208/240 one..plus buying it.]

I'm guessing you will spend most of $2K on whatever conversion method you happen to choose. Decision time.

I like Toms idea of single phase transformer and VFD - remember you will probably need a VFD rated for a 5hp motor to operate it from single phase source.

 

[templdl]

We're getting 3ph open delta from PG&E. We alas have a 480v 3ph 2 hp. pump in place 750ft down.

So I'm looking at 240->460 transformers. But most I see are wye on the LV side, delta on the 480. As far as I can see, the motor [http://www.franklin-electric.com/re...ModelNumber=234 325 94--S#model234-325-94--S] is 3-wire, so feeding that sole load with a delta leaves everything floating.

What are my options? Obvious would be a non-stock 240 delta-> 460 wye transformer. Others that the electrician & inspector will like...?

[Don't even ask about swapping the pump motor. $2K+ in labor to pull; & ~that to install a 208/240 one..plus buying it.]

Do you preceive it as a problem to to use a standard 480D-240D transformer, to corner ground the 480D? Corner ground the delta and run 3w to the motor along with an EGC is you normally would.
You could use a NEMA 3R TENV encapsulated 3kva such as the Eaton Y48G24T03N which has (2)-5%taps which should be around $1,500.
I'm sure there are other manufactures who have similar transformers.
Have you considered a drive isolation transformer? They are availablt as a 230D-460Y/266 w/(1)+5% and (1)-5% taps but are probably ventilated such as the Eaton MD075E89. It's a 7.5kva (an overkill of course) good for 5HP.

 

[Open Neutral]

Many good ideas; thanks. Am open to all suggestions.

• Considered VFD but long leads; also need load reactor. Also have a long (900+ ft) run to utility shed needing 240/120v. & was entertaining legality/cost of running one leg of 480 to it & putting small stepdown out there; less copper in ground.
  
• Ungrounded systems bother me. I can't justify that, it's just my lack of experience with same. Was reading https://xenforo.mikeholt.com/index.php?threads/143948/ with interest. The only issue with corner ground I can now see with same might be the Siemens EPS200 Solid State Overload Relay; will read up on that.
  
• Buck/boost & 208->480 is possible, but more iron/copper, more losses. Cost effectiveness TBD.
  
• Had not thought of open delta^2; i.e. two 1∅ 240->480 units. Already concerned about balancing issue; see possibility it would magnify that issue.

Thanks for all...

 

[Open Neutral]

Page 4 of Franklin's AIM manual suggests 2 - 2 kva single phase transformers set up in an open delta configuration as min size. Those should be a stock item in your area.

This may well be the best solution, if I can get things balanced. There's a potpourri of less expensive 240-480v single phase transformers in the right KVA. If I can find ones that are tapped....

 

[kwired]

This may well be the best solution, if I can get things balanced. There's a potpourri of less expensive 240-480v single phase transformers in the right KVA. If I can find ones that are tapped....

Nothing says you can't corner ground that if you want to. If you ground mid point of one phase you still have a wild leg of about 415 volts.

 

[augie47]

I think it's been discussed here previously and I have no technical data to back what I'm saying so you can take it with a grain of salt, but, submersible pumps don't seen to like open delta supplies.

 

[Open Neutral]

I think it's been discussed here previously and I have no technical data to back what I'm saying so you can take it with a grain of salt, but, submersible pumps don't seen to like open delta supplies.

The AIM mentions that, with precautions.
Am I helping by getting three 280->480 vs two, given the property feed is open delta?

 

[Open Neutral]

Nothing says you can't corner ground that if you want to. If you ground mid point of one phase you still have a wild leg of about 415 volts.

I meant "tapped, as in 235V, 240V, 245" flavor; to allow balancing the phase currents to the motor.

 

[templdl]

I think it's been discussed here previously and I have no technical data to back what I'm saying so you can take it with a grain of salt, but, submersible pumps don't seen to like open delta supplies.

What do you get when you loose one transformer when your supply is an open delta? Motors don't like that much. Should you have 3 transformers hooked in a delta and you loose one transformer then what?

 

[kwired]

I think it's been discussed here previously and I have no technical data to back what I'm saying so you can take it with a grain of salt, but, submersible pumps don't seen to like open delta supplies.

I don't know why that would be, they are still same thing as any other three phase induction motor. You have a higher voltage to ground on either a corner ground or on a wild leg depending on which you have, but motor does not use a neutral.

I meant "tapped, as in 235V, 240V, 245" flavor; to allow balancing the phase currents to the motor.

I thought we were talking open delta input and a 480 volt delta secondary derived from two single phase transformers. With that you will have three choices for the secondary, ungrounded, corner grounded, mid point of one phase grounded. You could possibly have taps on primary side to adjust voltage, but you just set them as you need - not much involved as far as topic of this thread goes.

Ungrounded needs ground detection system, corner grounded will have 480 to ground from two phases, mid point of phase will have two phases 240 to ground and a 415 to ground wild leg.

 

[templdl]

I don't know why that would be, they are still same thing as any other three phase induction motor. You have a higher voltage to ground on either a corner ground or on a wild leg depending on which you have, but motor does not use a neutral.



I thought we were talking open delta input and a 480 volt delta secondary derived from two single phase transformers. With that you will have three choices for the secondary, ungrounded, corner grounded, mid point of one phase grounded. You could possibly have taps on primary side to adjust voltage, but you just set them as you need - not much involved as far as topic of this thread goes.

Ungrounded needs ground detection system, corner grounded will have 480 to ground from two phases, mid point of phase will have two phases 240 to ground and a 415 to ground wild leg.

Wasn't this a 2hp motor? Remember the KISS principle. What is the reason not to corner ground it? What is the reason not to provide a closed delta either wirh a 240D-480D 3ph transofmrer of (3) 1ph transformers. Of one were to select (3) ph and hook then in a delta and they were size properly if one transformer would fail the other two would be able to carry the load which give one a security blanket.
We could beat this one do death.

 

[kwired]

Wasn't this a 2hp motor? Remember the KISS principle. What is the reason not to corner ground it? What is the reason not to provide a closed delta either wirh a 240D-480D 3ph transofmrer of (3) 1ph transformers. Of one were to select (3) ph and hook then in a delta and they were size properly if one transformer would fail the other two would be able to carry the load which give one a security blanket.
We could beat this one do death.

OP was looking for a way to KISS as well as keep cost below pulling and replacing the submersible with one that matches voltage available. Most of the alternatives are not going to save much from what I can see. KISS probably is either pull and change the submersible, use a three phase delta - delta transformer and likely corner ground the secondary, or go with single phase transformer and VFD. Most anything else will cost more than the pull the submersible and replace it option.


One time I had a small village with only single phase available at well house. They had a 20 HP 480 volt submersible well driven by a VFD that converted from 240 single phase to 480 three phase (all done in the drive). I don't remember exactly what was wrong with the drive but it cost something like $2500 to repair, and a new one was going to cost at least $7-8K. The village couldn't believe the cost but needed it repaired - we had to bring in a portable generator to get by with. I told them if they only had three phase power available at the worst they might have spent $6-700 for a new pump panel if it was just control problems that failed.

The cost of this VFD was hidden in the total bid back when the 20HP submersible was first installed so they had no idea how much repairs may end up costing some day if it failed. They would have been better off spending their money with POCO if necessary to get three phase to the site.

 

[templdl]

The AIM mentions that, with precautions.
Am I helping by getting three 280->480 vs two, given the property feed is open delta?

Does it matter if the service is an open delta? It's still 3 wires which will feed the primary if the step up transformer(s).

 

[templdl]

OP was looking for a way to KISS as well as keep cost below pulling and replacing the submersible with one that matches voltage available. Most of the alternatives are not going to save much from what I can see. KISS probably is either pull and change the submersible, use a three phase delta - delta transformer and likely corner ground the secondary, or go with single phase transformer and VFD. Most anything else will cost more than the pull the submersible and replace it option.


One time I had a small village with only single phase available at well house. They had a 20 HP 480 volt submersible well driven by a VFD that converted from 240 single phase to 480 three phase (all done in the drive). I don't remember exactly what was wrong with the drive but it cost something like $2500 to repair, and a new one was going to cost at least $7-8K. The village couldn't believe the cost but needed it repaired - we had to bring in a portable generator to get by with. I told them if they only had three phase power available at the worst they might have spent $6-700 for a new pump panel if it was just control problems that failed.

The cost of this VFD was hidden in the total bid back when the 20HP submersible was first installed so they had no idea how much repairs may end up costing some day if it failed. They would have been better off spending their money with POCO if necessary to get three phase to the site.

It's one of those things where you only are digging the hole deeper instead of biting the bullet and doing it right the first time.

 

[ptonsparky]

Do you have the control and pump panel for the well now? A vfd of that size is about the same cost of a PP. You do have added costs, but the reactor and transformer(s) will last long after the pump or vfd have died. Maybe several times over. Make sure you increase the size of a single transformer if you go that route.

 

[ptonsparky]

Does it matter if the service is an open delta? It's still 3 wires which will feed the primary if the step up transformer(s).

The secondary of the two transformers would still be open delta. IMO running that through the vfd would negate the problem with open delta.

But why use two transformers if you can get by with one?