Why use WYE in residential apartment buildings

[Hv&Lv]

Thinking about 'how to transition to 240/416Y' I think I came up with a hybrid system that clearly has unmarried parents.

Construct a 416Y system from 240V center tapped transformers, and bring out the center taps to serve 120V loads. Residences would be served with 120V L-G and 240V L-G. 416Y would be available for large 3 phase loads.

*tongue firmly in cheek*

-Jon

If I put that on the system every electrician around that works on it will call and complain the voltages aren’t right.


I put a 120/240 center tap in the middle of a 120/208 bank (commercial wood shop) to supply the house, and caused all sorts of grief for a few electricians .

 

[Hv&Lv]

Please keep in mind that this is something of a random musing thread, not something that I will ever implement.

The 'wagon wheel' does not use autotransformers; it uses a true isolating transformer arrangement. It is IMHO a 3 phase arrangement, but each phase has a full 120/240 center tapped secondary, allowing one to supply each apartment with 120/240 single phase rather than 120/208 pseudo single phase. This is no different than having 3 separate blocks each with their own single phase 120/240V transformer on a different distribution phase. The potential benefits are that the building presents a balanced 3 phase load to the utility, but with half the current on the 120V 'legs'. The customer sees a standard 120/240V. The downside is increased complexity, and possibly lower 'diversity' on each phase, since with a 120/208V system each phase is connected to more apartment feeders.

Here is the transformer diagram:
View attachment 2557526

The idea of a 'transition circuit' to 416/240V (where each residence just gets a single phase 240V L-N service) is to provide a hybrid system where each phase provides both 120 and 240V, but as L-N voltages, not standard split phase L-N-N 120/240V. Presumably the bulk of the loads (including receptacles) would be directly supplied with 240V (in the European fashion) but there would be a few 120V receptacles available.

The transformer diagram for this is:

View attachment 2557527

-Jon

I see 120v X0 to X2, 120v X0 to X1, 120v X1 to X2, 240V X2 to X2*, and 208v X2* to X3*, and so on...

 

[mbrooke]

Neat. How many wires? And the coloring?

I'm still setting my money on this:

 

[kwired]

If I put that on the system every electrician around that works on it will call and complain the voltages aren’t right.


I put a 120/240 center tap in the middle of a 120/208 bank (commercial wood shop) to supply the house, and caused all sorts of grief for a few electricians .

First part, there are North American voltages available there, but the 416 is kind of useless for most.

Second part I not sure I understand what you are describing?

add: and even if you had IEC 400 volt motors they are not going to like operating at 60 Hz.

 

[winnie]

First part, there are North American voltages available there, but the 416 is kind of useless for most.

Lots of 'dual voltage ' motors are rated 208-230/460

If wired for 460V but supplied with 416V, that is essentially the same as wiring in the lower voltage configuration and running at 208V

Jon

 

[Hv&Lv]

First part, there are North American voltages available there, but the 416 is kind of useless for most.

You have to take that comment in context with the post it was written under. If I build a bank like that believe me when I say we will be called by electricians working on the structure it’s serving saying the voltages aren’t right.

Second part I not sure I understand what you are describing?

I’m describing a three pot 120/208 bank built so that it will also put out 240/120 split phase. We have two of them on the system.

 

[kwired]

You have to take that comment in context with the post it was written under. If I build a bank like that believe me when I say we will be called by electricians working on the structure it’s serving saying the voltages aren’t right.


I’m describing a three pot 120/208 bank built so that it will also put out 240/120 split phase. We have two of them on the system.

I got that part, are you basically using half the winding of the 120/240 pot as one leg of the three phase secondary?

Never seen that but sounds like it would work. Depending on expected loading might need to be a bigger pot than the others of course.

 

[wwhitney]

So it's a wagon wheel with two spokes missing, 120 degrees apart?

Cheers, Wayne

 

[winnie]

I put a 120/240 center tap in the middle of a 120/208 bank (commercial wood shop) to supply the house, and caused all sorts of grief for a few electricians .

I'm curious why the electricians even noticed. I presume there were separate single phase and 3 phase service drops, not some sort of 4 leg service. The transformers weren't on the customer side of the meter?

Jon

 

[Hv&Lv]

I'm curious why the electricians even noticed. I presume there were separate single phase and 3 phase service drops, not some sort of 4 leg service. The transformers weren't on the customer side of the meter?

Jon

They looked up and saw three transformers.
the real confusion came when we told them they didn’t need a fifth clip meter base on the house

 

[kwired]

They looked up and saw three transformers.
the real confusion came when we told them they didn’t need a fifth clip meter base on the house

What if customer wants a single metered service, do you have one that will work for that?

 

[winnie]

What if customer wants a single metered service, do you have one that will work for that?

I doubt a standard meter is available to measure such a dual single/three phase service, but a standard 3 phase meter might be able to do it with a custom CT array. Wouldn't be Blondel compliant but would be as close as a standard single phase meter.

Jon

 

[Hv&Lv]

What if customer wants a single metered service, do you have one that will work for that?

?

I doubt a standard meter is available to measure such a dual single/three phase service, but a standard 3 phase meter might be able to do it with a custom CT array. Wouldn't be Blondel compliant but would be as close as a standard single phase meter.

Jon

no. It’s two different services. Not a dual.
a three phase self contained 120/208 goes to a shop From the bank.
the split phase self contained 240/120 goes to the house from the same bank.

 

[winnie]

My understanding was that it was separate metered services. I think kwired wanted to know if it would be possible to supply this as a _single_ metered service.

My answer is essentially 'anything is possible if you draw the design on the back of a big enough check', and that it could probably be done with standard equipment (meter and CTs) if the CTs were arranged in a non-standard fashion.

-Jon

 

[Hv&Lv]

What if customer wants a single metered service, do you have one that will work for that?

Not for that configuration. That would require 4 elements to meter correctly (Not possible with conventional meters) or three with metering errors (percentages dependent on loading)on the split phase element.

easiest to say it isnt possible and go on.

 

[winnie]

Not for that configuration. That would require 4 elements to meter correctly (Not possible with conventional meters) or three with metering errors (percentages dependent on loading)on the split phase element.

easiest to say it isnt possible and go on.

Actually easiest would be to have 2 meters and have the accounting department treat it as a single metered service

-Jon

 

[Hv&Lv]

Actually easiest would be to have 2 meters and have the accounting department treat it as a single metered service

-Jon

But then you wouldn’t get the two service charges...

 

[DrSparks]

More efficient and balances the POCO better.

Hexaphase is loads of added complexity for what is typically a none issue (ie 208 on 240 volt elements and motors).

The reduced output power is typically compensated for or not noticed.

230 volt motors are typically rated 197 min to 253 max, so 200 volts on an AC unit is technically within tolerance.

I notice the difference in resistive heating devices like water heaters and electric ranges. Not a fan. I've used boosting transformers in the past to compensate for low voltage,

 

[mbrooke]

I notice the difference in resistive heating devices like water heaters and electric ranges. Not a fan. I've used boosting transformers in the past to compensate for low voltage,

I think being who we are, we all do on this forum!

But, I also know of many apartments at 208 where folks have never said a word about it. Maybe they just don't know any different, but its no something that I've noticed to cause a stir.

On the plus side: At 208 volts it is VERY rare for 240 elements to fail.

 

[GeorgeB]

I notice the difference in resistive heating devices like water heaters and electric ranges. Not a fan. I've used boosting transformers in the past to compensate for low voltage,

As an engineer and support guy, I've worked with water heater manufacturers and specifiers of appliances for "large" apartment buildings. I've not seen any that don't offer heating elements (usually same cost in production quantities) for ranges/ovens/water heaters for 208V. I just looked at a State Industries water heater spec sheet; even "light duty" residential are offered in 208. Commercial units are catalog available at 277 and 480. Special order for 400.

Are you going to find them at big blue or big orange; not on the floor, but I'd gamble that they'd be available in 2-3 days. But an apartment building will not have home-owners doing plumbing or electrical in their units. Their professional maintenance will be aware of what is needed.