4 Wire Wye Vs 4 Wire Delta - New Construction

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mbrooke said:
Nope, direct current. :thumbsup:
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Ah, my wit was wasted. Never mind.

I don't think DC as in direct current will re-enter in the general sense. That argument was done an dusted decades ago.
There will be specif applications of course. Long distance HVDC transmission is one where it is advantageous. It is converted back to AC at the receiving end. Transforming down to lower voltages and switching is altogether more easily achieved with AC.
 
Besoeker said:
Ah, my wit was wasted. Never mind.

I don't think DC as in direct current will re-enter in the general sense. That argument was done an dusted decades ago.
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Of course; when technology was very primitive requiring induction, rotation and speed to be produced at the source for the entire system.

There will be specif applications of course. Long distance HVDC transmission is one where it is advantageous. It is converted back to AC at the receiving end. Transforming down to lower voltages and switching is altogether more easily achieved with AC.
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I disagree. With the mass implementation of co-generation, dropping cost in DC transformers, greater requirements to increase capacity of existing infastructure, greater need for system stability, and rectification in consumer products growing irregardless of internal components needing AC or DC, will steadily begin to make AC look more impractical. The amount of non linear load is further making AC less efficient. As is AC uses astronomical amounts of iron, more copper and higher losses compared to DC.
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Besoeker said:
What comprises a DC transformer?
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Your laptop/Ipad/cellphone charger is just one small example. :D Im serious. A DC transformer takes DC power, inverts it into high frequency AC, feeding a high frequency (ferrite) core transformer and then rectifies it back into DC. A capacitor and smoother circuit compliments the secondary rectification. DC to DC, or in the case if a charger 50/60 AC>DC>KHzAC>XFER>DC.


How exactly would you transform one voltage to another?
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Electromagnetic induction. Because a much higher frequency is used the transformer can be exponentially smaller for the same amount of power transferred. A real world example of this is a 40MVA 50Hz power transformer which will have about 18% more iron compared to a 60HZ 40MVA power transformer. This is because the lower the frequency the more core material is needed to prevent saturation.

The only hold back is the size, price and reliability (lack of mass scale testing) of HV semiconductors. Once HV IBGTs or similar semiconductors fall in price to the point where iron savings make a DC to DC unit more economical over a 50/60Hz transformer DC power systems will begin to take over.
 
mbrooke said:
Your laptop/Ipad/cellphone charger is just one small example. :D Im serious. A DC transformer takes DC power, inverts it into high frequency AC, feeding a high frequency (ferrite) core transformer and then rectifies it back into DC. A capacitor and smoother circuit compliments the secondary rectification. DC to DC, or in the case if a charger 50/60 AC>DC>KHzAC>XFER>DC.
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So then you have an inverter, a transformer, and a rectifier. Not to mention the far more onerous switching and fusing requirements. And would more correctly be called a DC-DC converter. The transformer part is still AC.

As I mentioned above, I can see the case for HVDC transmission over long distances. And sometimes not so long distances. There is one between France and England. The cross channel link. It is rated at 2GW, is bi-directional, but mostly runs at rated capacity in one direction. There's a bit of irony there but that's another story.

I can't see it for residential/commercial/industrial use. A DC motor is generally larger than a cage induction motor for the same power and the DC machine needs much more maintenance with the brushes needing to be regularly changed. As a company, we made permanent magnet "brushless" DC motors but they were horrendously expensive and only for special applications.

And, on costs, I have no idea how much a 1MVA 60 Hz transformer would compare with say, a 1MVA 10kHz transformer.
 
mbrooke said:
Your laptop/Ipad/cellphone charger is just one small example. :D Im serious. A DC transformer takes DC power, inverts it into high frequency AC, feeding a high frequency (ferrite) core transformer and then rectifies it back into DC. A capacitor and smoother circuit compliments the secondary rectification. DC to DC, or in the case if a charger 50/60 AC>DC>KHzAC>XFER>DC.




Electromagnetic induction. Because a much higher frequency is used the transformer can be exponentially smaller for the same amount of power transferred. A real world example of this is a 40MVA 50Hz power transformer which will have about 18% more iron compared to a 60HZ 40MVA power transformer. This is because the lower the frequency the more core material is needed to prevent saturation.

The only hold back is the size, price and reliability (lack of mass scale testing) of HV semiconductors. Once HV IBGTs or similar semiconductors fall in price to the point where iron savings make a DC to DC unit more economical over a 50/60Hz transformer DC power systems will begin to take over.
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A lot of equipment out there that would work fine on DC, but (in my world anyway) there may be more computers, electronic lighting/ballasts, other electronic items out there, but there is still significantly more power consumed by AC induction motors.
 
kwired said:
A lot of equipment out there that would work fine on DC, but (in my world anyway) there may be more computers, electronic lighting/ballasts, other electronic items out there, but there is still significantly more power consumed by AC induction motors.
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Correct, but increase more and more toward VFD.
 
Besoeker said:
So then you have an inverter, a transformer, and a rectifier. Not to mention the far more onerous switching and fusing requirements. And would more correctly be called a DC-DC converter. The transformer part is still AC.
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Switching and fusing could be done via solid state, or where the converter induces an artificial zero crossing.

As I mentioned above, I can see the case for HVDC transmission over long distances. And sometimes not so long distances. There is one between France and England. The cross channel link. It is rated at 2GW, is bi-directional, but mostly runs at rated capacity in one direction. There's a bit of irony there but that's another story.

I can't see it for residential/commercial/industrial use.
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Not yet, but as time moves forward it could happen.

A DC motor is generally larger than a cage induction motor for the same power
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I disagree, Ive seen universal motors lighter and smaller then an induction motor for the same power.

and the DC machine needs much more maintenance with the brushes needing to be regularly changed. As a company, we made permanent magnet "brushless" DC motors but they were horrendously expensive and only for special applications.
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Correct, which is why poly phase VFD motors are preferred where speed control and efficiency are desired. A washing machine would be one example.



And, on costs, I have no idea how much a 1MVA 60 Hz transformer would compare with say, a 1MVA 10kHz transformer.
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You might get close to lifting one of them :thumbsup:
 
Besoeker said:
Yes, when the application merits it. There are still a lot more fixed speed motors. And, even with a VFD, you still have that switching and fusing issue with DC.
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Refrigerators, washing machines, split AC units are all emerging with VFDs.
 
mbrooke said:
Refrigerators, washing machines, split AC units are all emerging with VFDs.
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Yet the industrial segment still has much more KVA connected to the grid via across the line induction motors. There is no need in dwellings or most light commercial for 100 HP plus motors, they add up fast. The bigger load in the homes and offices, etc. is typically the HVAC though.
 
kwired said:
Yet the industrial segment still has much more KVA connected to the grid via across the line induction motors. There is no need in dwellings or most light commercial for 100 HP plus motors, they add up fast. The bigger load in the homes and offices, etc. is typically the HVAC though.
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Correct, but VFD fed motors are popping many other applications. The amount of KVA being consumed by non-linear loads is going up every year and its far from a small fraction.


An example, this is from a new refrigerator service manual where just 10 years ago this was unheard of even on high end models:
 
mbrooke said:
Switching and fusing could be done via solid state, or where the converter induces an artificial zero crossing.
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For most of the applications I deal with, 3-phase industrial, there is a requirement for a contactor and an isolating switch.

mbrooke said:
Not yet, but as time moves forward it could happen.
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It could but I think the probability of it doing so is relatively small.

mbrooke said:
I disagree, Ive seen universal motors lighter and smaller then an induction motor for the same power.
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I rarely come across them so I can't comment

mbrooke said:
Correct, which is why poly phase VFD motors are preferred where speed control and efficiency are desired. A washing machine would be one example.
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Polyphase on a washing machine? All of those that I've encountered have been single phase. Admittedly it isn't that many.

mbrooke said:
You might get close to lifting one of them :thumbsup:
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My point was about relative costs.
 
Go 3 phase, 4 wire, Y transformer- everything will work on 208V, the only thing to watch for are instrument transformers in package equipment like roof top units, they may be 240 volt to 24 volt, but the motors should all be rated 208/240
 
cleatus_sask said:
Go 3 phase, 4 wire, Y transformer- everything will work on 208V, the only thing to watch for are instrument transformers in package equipment like roof top units, they may be 240 volt to 24 volt, but the motors should all be rated 208/240
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We have a bunch of old, 3-phase machine shop equipment that is going in. These are all pure motor loads (Index 40 Mill, Rockwell Drill presses, Carbide Grinders, Lathe, etc.) Do any of these older pure motor 3-phase loads have trouble with a WYE configuration?
 
Besoeker said:
Polyphase on a washing machine? All of those that I've encountered have been single phase. Admittedly it isn't that many.
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Single phase one or two speed with reversing and an automatic shift mechanism was the way to go.
But now, especially for front loaders, a multiple (~30?) pole pancake motor with direct drive to the tub is common practice. All VFD/pulsed DC operated. High torque and high speed from the same motor without gearing.
 
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