What is the correct amperage for line B in a 3 phase system?

[Awwtumn]

If you were to load A,B with 30 amps as you say, why do you think the conductors that feed a single load would carry current that exceeds the current in the load?
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You need to take a step back and simplify. Draw a single transformer winding driving a single load. Easy right? Now draw in an extra winding as would be in an open delta but no changes in the load. Why would this change anything? Finally, draw in the third winding to form the full delta. Again, no change.

Averagesupernova. Let's just assume the source is open delta and all the loads are cheap china made 230v items that were given free in hundreds of truckloads somewhere in Chinatown.

In the first illustration where the 3 lamps loads were connected in Delta. Each wire would draw 17.33A. While in the 2nd illustration where the 3 lamp loads were connected in series, the wires would only draw 30A.

Is it not the three 17.33A would add up to 52A and would draw more than 30A? Why is 3 phase more advantageous? Maybe the phase shift can produce less ampere overall? If yes. Does it mean building with Open Delta source and single phase loads connected in Delta would have cheaper electricity?

Baluncore, the source has the neutral in centertap grounded to the soil beneath the transformer poles. The loads don't have any neutral because the loads are all free china made 230v items in Chinatown but for loads with metal enclosure, the neutral is connected to the casing acting like ground since the neutral is connected to the soil at parking, so no worries about grounding whose concepts and safety purpose I have already explored in the past. I'm just scrutinizing the 3 phase source of the commercial building with all loads single phase and advantages and disadvantages of them.

If the single phase are all very inbalance, would the 3 phase electric meter register more values producing more expensive electricity? How does 3 phase meter work in monitoring each of the 3 phase and metering them?

I can influence the landlord to change to single phase source if there is no advantage in the open delta source, but maybe the electricity cost would be lowered in open delta source since the current drawn for the the three 10A lamps would be less than if connected in series (if true, see above).

Thanks a lot guys.

 

[Averagesupernova]

@Awwtumn my cell phone has a low battery so I can't reply in detail right now. I'll try to post within the next 4 hours. You have a few more misconceptions that need to be addressed.

 

[Averagesupernova]

You have some seriously wrong ideas here. First thing is the wires carry the current. The load draws it.
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Your three 10 amp loads in your first illustration in post 31 is no different than what has been discussed at length multiple times in this thread.
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The second illustration is where things go awry. You either have a 10 amp load or you don't. You don't have three 10 amp loads in series and come up with 30 amps. Current in a series circuit is always the same for all components. That being said, I'll ask you again, why would a 10 amp load across a single transformer winding with no other loads attached cause current other than 10 amps? I told you once it cannot but instead of you asking why or why not, you come at it from a different perspective asking the same question over. Why is this? Based on the fact that you don't understand this I cannot fathom how you can expect to understand even the most basics of 3 phase power and be serious about asking to have your building's service changed to single phase. The Poco won't do it anyway. They have better things to do than waste resources on that.
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Don't worry about your power consumption being metered incorrectly. Is that what this thread is really about?
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As has already been said in this thread, one advantage of three phase is the ability to transmit more power from source to load while using less copper. There are other advantages one being simpler, more efficient and reliable motors.
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Unbalanced loads on the Poco's transformers are not generally a problem. Unless you seriously change the function of a building to the point of having an actual electrician involved I wouldn't worry. If you do have an electrician involved they will have a good idea of the limits of the existing service and be in contact with the Poco. Open delta is generally a way to service a building that requires mostly single phase power and have a few light loads that require 3 phase. A full delta service will often involve powering large motors. Typically an industrial setting. Alot of Pocos will not supply delta service anymore. The favored configuration is wye connected transformers. It seems that it varies geographically what types of service a Poco will provide. I know there are places that they will readily set you up with delta if you want but other places it's an absolute not going to happen.

 

[Awwtumn]

You have some seriously wrong ideas here. First thing is the wires carry the current. The load draws it.
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Your three 10 amp loads in your first illustration in post 31 is no different than what has been discussed at length multiple times in this thread.
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The second illustration is where things go awry. You either have a 10 amp load or you don't. You don't have three 10 amp loads in series and come up with 30 amps. Current in a series circuit is always the same for all components. That being said, I'll ask you again, why would a 10 amp load across a single transformer winding with no other loads attached cause current other than 10 amps? I told you once it cannot but instead of you asking why or why not, you come at it from a different perspective asking the same question over. Why is this? Based on the fact that you don't understand this I cannot fathom how you can expect to understand even the most basics of 3 phase power and be serious about asking to have your building's service changed to single phase. The Poco won't do it anyway. They have better things to do than waste resources on that.
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Don't worry about your power consumption being metered incorrectly. Is that what this thread is really about?
-
As has already been said in this thread, one advantage of three phase is the ability to transmit more power from source to load while using less copper. There are other advantages one being simpler, more efficient and reliable motors.
-
Unbalanced loads on the Poco's transformers are not generally a problem. Unless you seriously change the function of a building to the point of having an actual electrician involved I wouldn't worry. If you do have an electrician involved they will have a good idea of the limits of the existing service and be in contact with the Poco. Open delta is generally a way to service a building that requires mostly single phase power and have a few light loads that require 3 phase. A full delta service will often involve powering large motors. Typically an industrial setting. Alot of Pocos will not supply delta service anymore. The favored configuration is wye connected transformers. It seems that it varies geographically what types of service a Poco will provide. I know there are places that they will readily set you up with delta if you want but other places it's an absolute not going to happen.

The load draws the current from the source. If the three 10A lamps in series draws 10A. And it connected in delta configuration draws 17.33A. Are you saying that if you average the 120 degree out of phase of the Delta load, it will draw the same ampere as the 10A in series?? They should be equivalent since the 3 pcs of 10A lamps draw the same power either in series or Delta load connection, but how are they equivalent?? Please give some values. Thanks.

 

[Averagesupernova]

Do you have any experience with circuit analysis? Kirchhoff's current laws? Stuff like that?
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With the 10 amp loads in delta you have three 10 amp loads each being driven by three separate transformers. It just so happens that those three loads and sources are sharing feeder conductors. If you understand the vectorial relationships of the three sources and understand basic circuit analysis you will understand why the currents come out the way they do in the feeder conductors.
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In your case of three 10 amp loads in series, what you really have is a single 10 amp load which is driven by a single transformer. There is the other transformer connected, but only one lead of the second transformer. The second transformer is contributing nothing in this case. Knowledge of basic circuit analysis would tell you this. So you have have a 10 amp load at whatever voltage is driving it, that's it.

 

[Averagesupernova]

Think of the shared conductors like this:
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If you are familiar with an amp clamp like these:

Then you realize you can clamp around a wire and measure the current it's carrying. You can also clamp around several wires and measure the current vectorially summed together. So if you had a situation where you had three separate transformer/load pairs all 120° out of phase you could group several wires and find your meter would tell you 17.33 amps when measuring two 10 amp loads from sources 120° out of phase. Maybe this makes more sense for you?

 

[Awwtumn]

Do you have any experience with circuit analysis? Kirchhoff's current laws? Stuff like that?
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With the 10 amp loads in delta you have three 10 amp loads each being driven by three separate transformers. It just so happens that those three loads and sources are sharing feeder conductors. If you understand the vectorial relationships of the three sources and understand basic circuit analysis you will understand why the currents come out the way they do in the feeder conductors.
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In your case of three 10 amp loads in series, what you really have is a single 10 amp load which is driven by a single transformer. There is the other transformer connected, but only one lead of the second transformer. The second transformer is contributing nothing in this case. Knowledge of basic circuit analysis would tell you this. So you have have a 10 amp load at whatever voltage is driving it, that's it.

For the three 10A loads in delta. How do you compute for the total power drawn in say the 3 delta transformers source? I just want to know how it compares to using just one transformer with three 10A loads in series. Is it more or less?

In commercial building 3-phase electric metering, they use Demand charge where the rate depends on the highest or peak kW used. So let's say all the one phase aircons were concentrated in one transformer or phase of the 3. Won't this increase the demand charge by increasing the peak kW used and hence the bill? Or does it somehow average out in all the 3 phase so it doesn't matter? This is what I want to know. Thanks.

 

[Averagesupernova]

For the three 10A loads in delta. How do you compute for the total power drawn in say the 3 delta transformers source? I just want to know how it compares to using just one transformer with three 10A loads in series. Is it more or less?

In commercial building 3-phase electric metering, they use Demand charge where the rate depends on the highest or peak kW used. So let's say all the one phase aircons were concentrated in one transformer or phase of the 3. Won't this increase the demand charge by increasing the peak kW used and hence the bill? Or does it somehow average out in all the 3 phase so it doesn't matter? This is what I want to know. Thanks.

Three 10 amp loads in delta are simply three 10 amp loads driven by their source voltage 240 V * 10 A = 2400 watts. Three separate loads so a total load of 7200 watts that the Poco will bill you for.
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Your question about three 10 amp loads in series makes no sense as I have already told you. The lights, motors, etc. used in mains wiring are not in series. If you have three 10 amp loads that are NOT balancing the delta supply there will either be all loads on one phase or two on one phase and one on another phase. Each load will have 240 volts across it and another total power for all three combined will still be 7200 watts.

 

[Averagesupernova]

@Awwtumn do you understand your electric bill? How many meters are listed?

 

[berkeman]

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