High Leg Delta

[Joethemechanic]

You don't replace the service transformer with the DIT, you just mount it next to the VFD, sized only for that drive, just like you would with a Line Reactor. No need to run 4 wires either, you just ground the X0 and leave it that way.

Yes I'm agreeing with you, it's the best solution. Almost zero lead time, and you need a line reactor anyway, so two birds with one stone.

The DIT is never going to waste enough power to mean squat compared to the costs of a serious upgrade like that.

@steve66
Is this a municipal, or a private sewage plant?

 

[jim dungar]

If you are buying a transformer, you could get one with with a 480Y/277 output and then use a 480V drive and motor. You would have to run the dollars though to see if it is cost effective.

 

[tortuga]

The DIT is never going to waste enough power to mean squat compared to the costs of a serious upgrade like that.

yeah it may not be much, but it aint zero, I looked up a Aluminum-wound 75 kVA with a no-load 375 W, full-load total 2829 W.
If Pump 'on' hours per year is 30% = 2628h
I came up with:
On vampire load: ~4,140 kWh/year
Off (idle) vampire load: 0.375 kW * 6132 h = ~2,300 kWh/year
Total vampire load: ~6,440 kWh/year
Per transformer per site * n number of sites.
If there is all three phases at the pole the cost of the utility providing a 240/139 wye bank is not what I would call major expense as your not changing voltage.
Its more just the bureaucratic hassle of seeing if they are willing.

 

[Joethemechanic]

Its more just the bureaucratic hassle of seeing if they are willing.

Yeah if the POCO is willing to foot the bill.

But if it's an open wye primary and it's a mile long, well that might be a hard sell.

I'm picturing this has to be a small plant if they are running it on 240 three. Although those aeration blowers can really use up the KWh. so maybe they use enough that the utility might eat the costs

 

[tortuga]

Yeah if the POCO is willing to foot the bill.

But if it's an open wye primary and it's a mile long, well that might be a hard sell.

I'm picturing this has to be a small plant if they are running it on 240 three. Although those aeration blowers can really use up the KWh. so maybe they use enough that the utility might eat the costs

Well yeah definitely I would not suggest it if the 3ph is not already there, if you have rural open delta, like the OP forget it. and here the wastwater district / water district pays the the utility for any upgrades.
What I was thinking of is suburban / urban setting with these largely un-attended lift stations or pump stations and 3ph right on the pole, here it was actually old 240 corner ground. I did not know if utilities could even provide 240/139 service, last summer I posted the question and @kwired had the solution to use 3X center tapped 277 cans, then parallel the windings, I am not a utility guy but you get the idea. You may not notice the little shacks and buildings but a small sized city here, somewhat flat has 48 pump stations.

 

[steve66]

For an update, I have heard back from the utility company. The photo of the pole I posted is not correct. The pad mounted transformer is actually fed from a different line of poles along a tree line that isn't anywhere near the road.

So, the transformer is actually fed with all 3 phases on the primary side, and the utility can change the pad mounted transformer to provide a 208Y/120V service.

I also heard back from the blower company manufacturer's rep, and they forwarded a PDF, which I also found here:

Open-Delta Systems Affect VariableFrequency Drives: To avoid premature drive failure, proper precautions must be taken when installing VFDs on open-delta supplies

Reprint of Article published in Pumps & Systems magazine, September 2012 issue, written by Dan Peters. 4 pages

www.yaskawa.com

 

[hillbilly1]

For an update, I have heard back from the utility company. The photo of the pole I posted is not correct. The pad mounted transformer is actually fed from a different line of poles along a tree line that isn't anywhere near the road.

So, the transformer is actually fed with all 3 phases on the primary side, and the utility can change the pad mounted transformer to provide a 208Y/120V service.

I also heard back from the blower company manufacturer's rep, and they forwarded a PDF, which I also found here:

Open-Delta Systems Affect VariableFrequency Drives: To avoid premature drive failure, proper precautions must be taken when installing VFDs on open-delta supplies

Reprint of Article published in Pumps & Systems magazine, September 2012 issue, written by Dan Peters. 4 pages

www.yaskawa.com

That’s unusual, I wouldn’t think a utility would do a pad mount delta service, they have to keep a spare transformer in the yard. Your area may have quite a few of them though.

 

[tortuga]

For an update, I have heard back from the utility company. The photo of the pole I posted is not correct. The pad mounted transformer is actually fed from a different line of poles along a tree line that isn't anywhere near the road.

So, the transformer is actually fed with all 3 phases on the primary side, and the utility can change the pad mounted transformer to provide a 208Y/120V service.

If the other loads can handle 208 I'd suggest going that route.
You can ask the POCO to set the taps as high as they go (5%) so you'd get more like 218/126 or even 220/127 A 240V motor that does not support 208 would probably run fine on 218.
Do a survey of all the motors and control transformers, power supplies etc on the 240 side and see if there is any issues dropping to 208.

 

[ggunn]

Well there you go open delta pad mount.

Does anyone make such a thing? I've never seen one; all the open deltas I have seen were pole mounted - one transformer center tapped for the A and C phases with a neutral and a smaller one for the B phase.

 

[tortuga]

Does anyone make such a thing? I've never seen one; all the open deltas I have seen were pole mounted - one transformer center tapped for the A and C phases with a neutral and a smaller one for the B phase.

I have no idea, in 2026 I'd be more interested in utilities offering a 240/139 wye, for the 112.5 kVA they look to list for about $4k more than the equivalent 208/120 model.
EDIT: That price difference mainly is because the 240 model seems only available with copper windings, the 208 model is aluminum windings.

 

[MTW]

The only pad mount open delta I have encountered was made up with two single phase units placed next to each other.

 

[hillbilly1]

Does anyone make such a thing? I've never seen one; all the open deltas I have seen were pole mounted - one transformer center tapped for the A and C phases with a neutral and a smaller one for the B phase.

Probably a full delta, and even then I would think it would be rare for a utility. I have a lot of full delta’s I put in at one plant that I do a lot of work at, most of the loads are 230 volt machines. I have it tapped low on the input. Very little 120 volt loads.

 

[jim dungar]

I am amazed the number of electricians that treat center-tapped delta and open-deltas as synonyms. Evidently they do not realize one does not preclude the other.

 

[Birken Vogt]

I have seen a new pad mount 240 delta. I don't think it was open delta though. It was to a small water department in an area destroyed by a forest fire. Surely they had an open delta pole bank in there before but after the fire everything was rebuilt underground. PG&E has so much horsepower I am sure they can get any tx they want.

 

[herding_cats]

You can easily convert your 240D into 208Y with a transformer. Add a line reactor rated to the same Amperage as the transformer, add 20%.

 

[Joethemechanic]

How many HP are these blowers?