Transformer vs Utility

Status
Not open for further replies.

jake.hagm

New member
Right now we have 3 services going into the facility. First 1600A 480v 3P 4W. Second 400A 480V 3P 4W. Third 100A 230V 1P 3W, for some lighting convince receptacles and some split unit A/C. My math says Available Power (Watts) on the third service would be 2300W. Now If we Changed to a 3 Phase Transformer 480/208v and eliminated the third utility service 2300w/208*1.732 we would need a 23KvA Transformer? Rounded up to 30KvA. 480v 40A Primary and 80A Secondary?
 

iwire

Moderator
Staff member
Location
Massachusetts
I have to say it is not clear to me what the question is.

But changing the voltage will not change the capacity of the supply.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
If I read correctly you are looking at eliminating the 3rd service and feeding the loads with an in-house transformer... a common practice.
In doing so you could look at the present actual load or provide the same available current which, as you have calculated, is 100 X 230 or 23kw. As you noted the next "standard' size would be 30kva and your primary secondary currents are close. Follow Art 450 and 240 for selection of oveurrent devices and conductors.
Keep in mind, by changing to 3 phase you have selected a transformer with a 208 secondary vs 240 so make sure your equipment is compatible. (You can also elect to choose a Single-Phase transformer giving you 240v at slightly different currents or a 240/120 three phase giving you a high-leg secondary).
Also keep in mind there are some power losses with transformers which you will now be paying so there are some "hidden" cost in comparing the two.
 

Electric-Light

Senior Member
Right now we have 3 services going into the facility. First 1600A 480v 3P 4W. Second 400A 480V 3P 4W. Third 100A 230V 1P 3W, for some lighting convince receptacles and some split unit A/C.

You have 24kVA available on the third service. Where is this derived from? If you tap off from 480v, whatever dips and flicker presented on 480v by industrial equipment gets passed onto 120v and cause a flicker and your own transformer might not have a low of impedance as the utility's and the cycling of AC units can also cause flicker on the secondary side.

My math says Available Power (Watts) on the third service would be 2300W. Now If we Changed to a 3 Phase Transformer 480/208v and eliminated the third utility service 2300w/208*1.732 we would need a 23KvA Transformer? Rounded up to 30KvA. 480v 40A Primary and 80A Secondary?

No, the kVA rating on a 3 ph transformer is the combined total of three. You're wired for single phase three wire and you'll be leaning on two legs of a tripod so you're going to have to oversize 50%. The third leg is basically capped off unless you have a three phase load.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
No, the kVA rating on a 3 ph transformer is the combined total of three. You're wired for single phase three wire and you'll be leaning on two legs of a tripod so you're going to have to oversize 50%. The third leg is basically capped off unless you have a three phase load.
Not necessarily economical because of the specialized transformer connection required, but the Leyton 3-2 circuit can supply a single phase load with power drawn equally from the three source phases.

For the math, see http://wikivisually.com/wiki/User:Hugh_Leyton/sandbox
 

Electric-Light

Senior Member
Not necessarily economical because of the specialized transformer connection required, but the Leyton 3-2 circuit can supply a single phase load with power drawn equally from the three source phases.

Doesn't relate to what I was trying to say, which is..

1.) A 50kVA 3 phase transformer can not provide 50kVA into single phase 3 wire system.

2.) You can't hook all three phases into a 1P3W panel that is currently fed from his 100a service. Multi-family uses multiple panels so you can alternate AB, BC, CA over multiple panels.

I am unaware of a simple passive device that can spread one single large single phase load over three phases. From what I know you need to use an MG-set and AC-DC-AC type converter.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I am unaware of a simple passive device that can spread one single large single phase load over three phases. From what I know you need to use an MG-set and AC-DC-AC type converter.
The Leyton 3-2 circuit is a simple passive device that uses three transformers but no special electronics or convertors.
It powers a single phase load equally from all three phases of a three phase source.
You are correct that there is no solution using a single transformer.
If you do not believe that what I say can be done, please read the description by Hugh Leyton that I linked to.

It is a similar situation to the Scott-T conversion between three phase and two phase but it has the major difference that it is NOT reversible, that is it cannot derive three phase output from single phase input. (Which would be prohibited by the phasor mathematics involved, similar to dividing by zero.)
 

Electric-Light

Senior Member
The Leyton 3-2 circuit is a simple passive device that uses three transformers but no special electronics or convertors.
It powers a single phase load equally from all three phases of a three phase source.
You are correct that there is no solution using a single transformer.
If you do not believe that what I say can be done, please read the description by Hugh Leyton that I linked to.
:roll: not trying to be rude but it seems like it's just a use of Scott T transformer which has always been able to provide two single phase circuits. Does anything even mentions Leyton in reference other than himself? I don't believe it can provide balanced load on three phase side when the heaviest loads are phase to phase.

It is a similar situation to the Scott-T conversion between three phase and two phase but it has the major difference that it is NOT reversible, that is it cannot derive three phase output from single phase input. (Which would be prohibited by the phasor mathematics involved, similar to dividing by zero.)

It's already pretty much established that you can not use a passive static converter to produce a three phase power that is actually 120 degrees apart both with the Scott-T or this thing.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
:roll: not trying to be rude but it seems like it's just a use of Scott T transformer which has always been able to provide two single phase circuits. Does anything even mentions Leyton in reference other than himself?



It's already pretty much established that you can not use a passive static converter to produce a three phase power that is actually 120 degrees apart both with the Scott-T or this thing.

1. The Scott-T converts, in either direction, between three phase (120 degree) and two phase (90 degree, quadrature).It is of no use whatever in converting from three phase to single phase, except in that you could choose not use one of the two derived phases. If you do that you have wasted transformer capacity and you have not pulled any power consumed by that single phase equally from all three of the incoming phase lines.
2. If you try to drive the two phase side of the Scott-T with only single phase, you will certainly not get three phase output. If you try to drive both of the two phase windings from the same phase, you are likely to create an effective short circuit.
3. The goal of the Leyton 3-2 circuit is to take incoming three phase power, either wye or delta, and derive a single phase output that pulls power in a fully balanced way from all three of the input phases (equal and properly phased currents in each of the three line conductors.)
4. Nobody ever said that the Leyton circuit could be reversed to produce three phase from single phase. In fact I explicitly stated that it cannot be used that way.
5. One consequence of the above (4.) is that you can use it to take a standalone three phase generator and connect it in a synchronized fashion with a single phase grid connection. But you cannot do the same with a three phase grid interactive inverter, since there will be no three phase reference voltage for the inverter to synchronize to.
6. It is not a common circuit, and hence Leyton was able to name it himself. The fact that it is seldom used and little referenced (except in a couple of very long threads on this forum) is probably the result of the cost of the three transformers compared to the cost of rewiring a generator to single phase or just accepting an unbalanced single phase output at reduced capacity.
7. If you do not believe the math behind it, you are free to build a model and watch it work. I, for one, am satisfied with the math.

It's already pretty much established that you can not use a passive static converter to produce a three phase power that is actually 120 degrees apart both with the Scott-T or this thing.
8. If you start with two phase, you can use the Scott-T to produce fully balanced, 120 degree phased output. It was originally used that way to deliver three phase power from a two phase service, as well as the reverse. But not from a single phase input. That was never an issue in this thread.
 

Electric-Light

Senior Member
3. The goal of the Leyton 3-2 circuit is to take incoming three phase power, either wye or delta, and derive a single phase output that pulls power in
As does Scott T transformer. I think someone like gar could enlighten on this.

6. It is not a common circuit, and hence Leyton was able to name it himself. The fact that it is seldom used and little referenced (except in a couple of very long threads on this forum)
You wouldn't happen to be Leyton, would you? just checking. Metal cage is known and accepted by the name Faraday Cage. I don't think it would be appropriate if you made a tiny bit of alteration to it and started referencing to it as "The GoldDigger cage" just so people would have to Google it to make sure they stumble into {{primary reference}}{{citespam}}

The self promoted sales pitch says American NEC 240/120v from three phase.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
The self promoted sales pitch says American NEC 240/120v from three phase.

I really find it hard to understand the motive for your hostility.
AFAIK Hugh Leyton is not trying to commercialize the circuit design and has not applied for a patent on it.
Putting up a rather hard to find blog about an interesting circuit discovery is IMHO not "self-promotion".
And what is incorrect or offensive about the reference to American NEC 120/240 [to use the more common reference] from three phase?

mobile
 

Electric-Light

Senior Member
I really find it hard to understand the motive for your hostility.
AFAIK Hugh Leyton is not trying to commercialize the circuit design and has not applied for a patent on it.
Putting up a rather hard to find blog about an interesting circuit discovery is IMHO not "self-promotion".

I have never heard of it. The search result relating to Leyton and transformer is littered with forum posts and his own edits on open wikis without third party editorial oversight. But it's not the first time I've seen someone do a concept IP spam and call something a Rhonda Coil that's just a very close approximation to force audience to search for it and get them to read his posts peppered all over the web.

And what is incorrect or offensive about the reference to American NEC 120/240 [to use the more common reference] from three phase?
mobile
I didn't say it's incorrect or offensive but it draws an illusion of novel idea when uniqueness is highly questionable.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I didn't say it's incorrect or offensive but it draws an illusion of novel idea when uniqueness is highly questionable.

Show me any other suggestion of that combination of transformers or any other passive circuit that performs the same function and I will grant your questioning its uniqueness.
Till then, I say unique.

Point to consider: You stated in your first comment that a Scott-T does the same thing, when quite obviously it does not.
 

Ingenieur

Senior Member
Location
Earth
Is there a connection diagram/schematic and phasor diagram for this leyton setup?
looked on the website and too much garbage and no simple pictures
they do show a scott setup
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Is there a connection diagram/schematic and phasor diagram for this leyton setup?
looked on the website and too much garbage and no simple pictures
they do show a scott setup

The best I have found was on the sandbox website. Although there were probably some good graphics on earlier threads in this forum.

mobile
 

Ingenieur

Senior Member
Location
Earth
went thru the whole site
the leyton 3-2 figure is actually a scott

the premise
3 each 1 ph xxx-120/240 transformers arranged in a 3 ph bank to yield 1 ph 120/240 secondary output from 3 phase primary input
regardless of loading it is inherently balanced, ie, the load is equally distributed over the 3 transformers regardless of the output load distribution

if we had a connection diagram we could determine the output
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
went thru the whole site
the leyton 3-2 figure is actually a scott
No it is not. If the turn ratios are different or if the topology is different, it is a different circuit.
The Scott-T will not make a balanced load on all three input lines if only one of its output phases is loaded.
 
Status
Not open for further replies.
Top