Balancing single phase loads from 3 phase

[Besoeker]

I believe he said earlier that this facility once was supplied from an open delta system - so what he meant was the center phase in disconnects and panelboards would have been where the high leg was landed at that time. That was the reason for not placing any single phase loads on the center phase. Nobody changed these single phase loads to balance them when the delta was converted to wye.

From a couple of posts back:

I had my maint man work a little on the electrics today. He balanced the single phase loads a little more evenly.

But not really pertinent to the point about "burning a ton of electricity".

 

[GoldDigger]

Both outside legs?
The transformer, being Y has three outside legs. Three phases.


That would give you a line current capacity of about 625A. (Assuming 208V line to line.) Possibly greatly more than you need for the CNC machines. But what else does it feed?


You simply can't calculate it that way.


Transformer losses are normally quite small. They come in two kinds. Iron loss (Fe) and copper loss (Cu).
The Fe loss is typically less than 1% - for loss calculations I work on 0.7%. The Cu loss might be about 1% at the full rating of the transformer. And it is square law with current. Half the current is quarter of the losses. In your case, if you are running your 225kVA unit at about 10% (1/10) loading, you'd be down to 1% of full load Cu losses. That is 1% of 1%.

In short, your 225kVA transformer losses are pretty unlikely to be burning a ton of electricity. Reducing the rating and/or rebalancing would be, at best, tinkering around at the margins for energy savings.

They are on the outside of the three bus panel. And the were once connected line to neutral on the two hot leads of the 120/240 winding of the lighting transformer in the high leg 240 delta system which the wye replaced.
All he is saying is that there were no 120V connections to what had been the high leg in that old service.

 

[Besoeker]

They are on the outside of the three bus panel. And the were once connected line to neutral on the two hot leads of the 120/240 winding of the lighting transformer in the high leg 240 delta system which the wye replaced.
All he is saying is that there were no 120V connections to what had been the high leg in that old service.

I don't recall a lighting transformer being mentioned, just the 225kVA unit. Manifestly musta missed that mention.

 

[GoldDigger]

I don't recall a lighting transformer being mentioned, just the 225kVA unit. Manifestly musta missed that mention.

It was mentioned only later as the previous service type used with the same panels and wiring before the 208Y/220 service was brought in as a replacement.
See posts #13 and #16.

 

[Besoeker]

It was mentioned only later as the previous service type used with the same panels and wiring before the 208Y/220 service was brought in as a replacement.
See posts #13 and #16.

So, not really relevant now if it has been replaced?
BTW, assume you mean 208Y/120?

 

[GoldDigger]

So, not really relevant now if it has been replaced?
BTW, assume you mean 208Y/120?

Relevant only in that it explains the phase usage pattern the OP was originally asking about. And yes, 208Y/120. Fat fingers.

 

[GITRDUN]

Let me clarify things a little. I think i have likely confused some people.

Our origional setup was a 240v high leg delta. All single phase loads were connected to one of the two outside legs + neutral, and three phase loads obviously connected to all three legs but had to have the middle leg connected in the middle at the machinery. We now have a 480Wye Tx connected to the service and a 225kva 208Wye Tx drawing from the 480. And so we are trying to balance the single phase loads a bit more evenly across all three legs of the 208.

Before balancing things out a bit here are the amp measurements we took with about 80% of single phase and 100% of dual phase loads running with only two three phase loads running.
Blue leg - 60A
Middle - 6A
Red - 38A
Neutral - 35A

Our machinery is all three phase and there is normally no more than about 5 machines pulling from the 208 at any given time each pulling about 15A or so fully loaded.

So with that can someone tell me how much transformer capacity we were using?

 

[Smart $]

...

So with that can someone tell me how much transformer capacity we were using?

With the measurements provided, about 12.5kVA or about 5.5%

 

[Besoeker]

With the measurements provided, about 12.5kVA or about 5.5%

I agree.
But then 5 machines pulling from the 208 at any given time each pulling about 15A or so fully loaded.......

 

[Smart $]

I agree.
But then 5 machines pulling from the 208 at any given time each pulling about 15A or so fully loaded.......

He didn't note whether that was 1? or 3?. His spec's are haphazard. He mentions 3? machines without current. Then he mentions 208 with current but not phases.

(5) 15A 208 3? = 27.0kVA
(5) 15A 208 1? = 15.5kVA

Needs a load calculation... and start by listing each load and its nameplate data.

 

[Besoeker]

He didn't note whether that was 1? or 3?. His spec's are haphazard. He mentions 3? machines without current. Then he mentions 208 with current but not phases.

(5) 15A 208 3? = 27.0kVA
(5) 15A 208 1? = 15.5kVA

Either way, neither accords with the 12.5 kVA his measurements give.

Needs a load calculation... and start by listing each load and its nameplate data.

Agreed.