Another High Leg question

[dicklaxt]

I have read many posts dealing with this type service and in reading on the net I find many refernces to it and how is is outdated and found occasionally in older dwellings/commercial sites.

My question is this:why is this wiring system not upgraded ?
When I read about it being outdated I would think not often used etc would ear mark it for the trash pile.

dick

 

[brian john]

Why should a local utility replace their distribution at their cost when a customer is not requesting it?

Why should an end user incur this cost when the existing distribution is adequate for their needs?

 

[jrannis]

It still is a really good and cheap way to have a three phase service

 

[dicklaxt]

Without the high leg you have a 3 phase system,I don't understand your answer.


dick

 

[roger]

Without the high leg you have a 3 phase system,I don't understand your answer.


dick

You would have a high leg with a center grounded Delta three phase system, you will not have a high leg with a Wye three phase system but they are both three phase configurations

Roger

 

[dicklaxt]

Sure is so, but that wasn't the statement,it was a cheap way to have a three phase system,,,,,,,,,,,,,,,,,,,,,so now I ask why would a 3 phase delta with one center tapped phase for 120V and the capabilty of 208 high leg be cheaper to manufacture than a 3 phase delta wye?

dick

 

[roger]

A Delta can be acheived with two windings whereas a Wye needs three.

Roger

 

[don_resqcapt19]

Sure is so, but that wasn't the statement,it was a cheap way to have a three phase system,,,,,,,,,,,,,,,,,,,,,so now I ask why would a 3 phase delta with one center tapped phase for 120V and the capabilty of 208 high leg be cheaper to manufacture than a 3 phase delta wye?

dick

This is not typically supplied from a single three phase transformer. It is normally supplied from single pots connected as a three phase bank.

 

[gar]

080726-1358 EST

dicklaxt:

Wild leg deltas are very common in our area. Many applications have a high load need for single phase 120-0-120, but also need three phase. In the case of our shop we have a 100 KVA 120-0-120 transformer and a smaller 240 V transfomer, probably 75 KVA, to supply the wild leg for 3 phase. This provides a grounded delta via the single phase center tap, and an easy way to increase three phase power by the addition of another small transformer.

Note: also the 240 is marginally better than 208 for powering motors. Less voltage drop for the same wire size and HP.

.

 

[dicklaxt]

Roger ,guess I'll go see if I can find that transformer wiring unless you got one handy,i'm getting more confused,,I'm hearing two here and three there.

later

 

[roger]

Dick, click HERE for a four wire open Delta.

Roger

 

[dicklaxt]

Aha!!!!!The confusion clears,,,,this is what I had envisioned but 3 phase's are used in the 4W Open Delta and not two as you stated.


Quote
A Delta can be acheived with two windings where as a Wye needs three,,,or were you referencing something else,thats were the confusion started.

dick

 

[roger]

Aha!!!!!The confusion clears,,,,this is what I had envisioned but 3 phase's are used in the 4W Open Delta and not two as you stated.



dick

Dick, you need to read a little slower, I never stated two phases are used, I stated two windings are used.

Roger

 

[dicklaxt]

Right you are my mistake,,,,,,,,,,,,,,,,,now I'm smarter than I was 2 minutes ago ,thanks all for the explanations but is it still cheaper to manufacture?WAIT!!!!Do I not see three windings in the wiring diagram confused again.
I guess for the options available it probably is ,boy I'm getting smarter by the minute.:grin:

dick

 

[roger]

Right you are my mistake

I think I heard my wife say that before but never anyone on the forums. :grin:

Roger

 

[charlie]

. . . Do I not see three windings in the wiring diagram . . .

Yes, you do not see three windings (it is best not to ask a question with a negative, it makes the answer seem wrong). The primary is connected as an open wye and single bushing transformers are normally used where the grounded end of the primary coils are connected internally to the grounding point inside the tank. The secondary side is connected as shown in the link. Notice that you get 240 volts from the red B? to the brown C? even though the winding is not there to produce the voltage. Also, the red color is not a code violation if the system is the same color coding throughout for that voltage and if there are two voltages, the color coding scheme is marked for both voltages.

 

[quogueelectric]

I think I heard my wife say that before but never anyone on the forums. :grin:

Roger

I was told that they are taught in wife school to never say that unless it is to secure national security.

 

[dicklaxt]

Well good morning all you teachers,I'm back for another class in understanding.I am not trying to be a PITA but this is not coming to the front and I'm just a little bit smarter than the average bear.

If I see a reference to phases, A-B-C,three line colors, red-yellow-brown ,three blue windings(?) connected by two white jumpers and voltage reference's of 3 phase 240V,2- single phase 120V and 1-single phase 208v.

How can you say that doesn't add up to 3 windings?

Get a shovel and hit me in the place that hurts most but I'm still not hearing or seeing what you all are saying.

Going back to scratching.

dick

 

[gar]

080727-0732 EST

dicklaxt:

An open delta uses two single phase transformers. One transformer input (primary) is connected to one phase of the three phase supply. The second transformer is connected to one of the other supply phases. It does not matter whether the primary is connected Y or delta except with respect to transformer turns ratio. However, you would not connect one primary between A and B, and the other from A to N.

The two secondaries are connected delta. One of the secondaries is center tapped and the center tap is grounded, and called neutral.

The center tapped transformer is a single phase supply. Some may call it two phase, but I do not like that usage. There is no way that secondary in any combination can cause an induction or synchronous motor to self-start without additional phase shifting components like a capacitor. It is true that when referencing voltage measurements from the center tap that the two voltages from the end leads are 180 degrees out of phase.

.

 

[roger]

Dick, here is another illustration showing the two windings that may be easier to understand.

Roger