From my latest Electrical mag.
We already have it here in the HV distribution.

https://www.ebmag.com/dc-presents-a-strong-case-for-more-sustainable-and-energy-efficient-buildings/

 

From my latest Electrical mag.
We already have it here in the HV distribution.

https://www.ebmag.com/dc-presents-a-strong-case-for-more-sustainable-and-energy-efficient-buildings/

Sure, make the entire electric wiring infrastructure obsolete by designing for class 4 power systems with no track record for reliability or performance.

The comment about HVAC DC motors being 50% more efficient that AC motors is a classic slight of hand. Modern BLDC motors are actually a synchronous AC motor. The controller takes DC input from a utility AC to Dc converter for external commutation while the Brushed DC motor has internal commutation for its AC requirements. The saving is because of the ability to optimize air-flow by efficiently adjusting fan speeds instead of one speed induction motor, duty cycle ON/OFF modes. It's not because of any magical difference between motor source power types.

https://www.tesla.com/blog/induction-versus-dc-brushless-motors

Both DC brushless and induction drives use motors having similar stators. Both drives use 3-phase modulating inverters. The only differences are the rotors and the inverter controls. And with digital controllers, the only control differences are with control code. (DC brushless drives require an absolute position sensor, while induction drives require only a speed sensor; these differences are relatively small.)

One of the main differences is that much less rotor heat is generated with the DC brushless drive. Rotor cooling is easier and peak point efficiency is generally higher for this drive. The DC brushless drive can also operate at unity power factor, whereas the best power factor for the induction drive is about 85 percent. This means that the peak point energy efficiency for a DC brushless drive will typically be a few percentage points higher than for an induction drive.

In an ideal brushless drive, the strength of the magnetic field produced by the permanent magnets would be adjustable. When maximum torque is required, especially at low speeds, the magnetic field strength (B) should be maximum – so that inverter and motor currents are maintained at their lowest possible values. This minimizes the I² R (current² resistance) losses and thereby optimizes efficiency. Likewise, when torque levels are low, the B field should be reduced such that eddy and hysteresis losses due to B are also reduced. Ideally, B should be adjusted such that the sum of the eddy, hysteresis, and I² losses is minimized. Unfortunately, there is no easy way of changing B with permanent magnets.

In contrast, induction machines have no magnets and B fields are “adjustable,” since B is proportionate to V/f (voltage to frequency). This means that at light loads the inverter can reduce voltage such that magnetic losses are reduced and efficiency is maximized. Thus, the induction machine when operated with a smart inverter has an advantage over a DC brushless machine – magnetic and conduction losses can be traded such that efficiency is optimized. This advantage becomes increasingly important as performance is increased. With DC brushless, as machine size grows, the magnetic losses increase proportionately and part load efficiency drops. With induction, as machine size grows, losses do not necessarily grow. Thus, induction drives may be the favored approach where high-performance is desired; peak efficiency will be a little less than with DC brushless, but average efficiency may actually be better.

The ebmag article is mainly marketing hype IMO.

 

You still have the inefficiencies in converting the AC to the distributed 450V HV dc, and then to the lower voltages required by most devices using DC.
Not sure you gain much over converting AC directly to the low voltage DC.

 

I thought Nikola Tesla won that argument with Thomas Edison many years ago!

 

It is definitely a significant advantage here in the long distance power transmission.

 

It is definitely a significant advantage here in the long distance power transmission.

Yes, in a few ways even when the distance is not long. You don't need to a synchronous network of generators and you can easily convert to the local AC standard(s).
https://en.wikipedia.org/wiki/Shin-Shinano_Frequency_Converter

The HVDC back-to-back facility Shin Shinano uses line-commutated thyristor converters. The station houses two converters, one of which opened in December 1977,[1] the other in 1992. The original 1977 converter was one of the first thyristor-based HVDC schemes to be put into operation in the world and used oil-insulated, oil-cooled outdoor thyristor valves supplied by Hitachi (60 Hz end) and Toshiba (50 Hz end).

 

When you consider the number of low voltage wall warts around the house why don’t we distribute low voltage DC?

Heck, even wall sockets now come with USB charging ports.

 

When you consider the number of low voltage wall warts around the house why don’t we distribute low voltage DC?

Heck, even wall sockets now come with USB charging ports.

You can't distribute low voltage DC at the device usage voltage because it varies so much from device to device and voltage drops with low voltages like 5VDC and higher power requirements. So there must be some sort of standard DC bus voltage close to current AC RMS voltages to utilize at least some of the current wiring infrastructure, electrical parts and a wall socket DC to DC conversion module much like the AC to DC wall wart for most devices. A singe dc system would still require dc to dc converters.

The main problem with higher voltage/power DC distribution (> few hundred watts) is contact arcing on live circuits.

 

All of that is going to change when we move to high temperature super conductivity.

 

All of that is going to change when we move to high temperature super conductivity.

Sure, that's right after we have commercial fusion reactors. I have a DC distribution system in the house for surveillance 12vdc devices and sensors. it's a solution looking for a problem.

 

I thought Nikola Tesla won that argument with Thomas Edison many years ago!

Edison invented lots of stuff, but if he'd have invented the power MOSFET, it might have swung the argument the other way.

One thing that has not been mentioned here is that a 50Hz or 60Hz grid needs some large rotating machines with lots of intertia to keep it stable. If power generation comes from lots of isolated small generators, especially if they all use electronics to generate the AC such as PV and wind turbines, keeping the frequency stable becomes a problem, which would be solved by DC power transmission.

 

Edison invented lots of stuff, but if he'd have invented the power MOSFET, it might have swung the argument the other way.

One thing that has not been mentioned here is that a 50Hz or 60Hz grid needs some large rotating machines with lots of intertia to keep it stable. If power generation comes from lots of isolated small generators, especially if they all use electronics to generate the AC such as PV and wind turbines, keeping the frequency stable becomes a problem, which would be solved by DC power transmission.

I think I pointed out the frequency issue on post #6. The lack of mechanical inertia is not 100% a good thing.
https://forum.allaboutcircuits.com/threads/solar-developments.41398/post-590329

 

Sure, that's right after we have commercial fusion reactors.

The two holy grails of modern science is cold fusion and room temperature superconductivity.
When we have both they will radically revolutionize every aspect of human activity.

 

The two holy grails of modern science is cold fusion and room temperature superconductivity.
When we have both they will radically revolutionize every aspect of human activity.

True, it will also make it easier to kill each other like most technological breakthroughs. Fusion powered directed energy weapons anyone?
https://www.inverse.com/innovation/laser-weapons-directed-energy


Imagine a much deadlier version of this miniaturized to the size of a pistol.

 

From my latest Electrical mag.
We already have it here in the HV distribution.

https://www.ebmag.com/dc-presents-a-strong-case-for-more-sustainable-and-energy-efficient-buildings/

There had been discussions on using DC for longer length transmission lines due to the fact that there is no skin effect.
From what i remember there were advantages but only in certain geographical areas.

 

I’m asking Santa for a superconducting Mr. Fusion Xmas 2042. Not sure what I can do with it in the nursing home, though.

 

I’m asking Santa for a superconducting Mr. Fusion Xmas 2042. Not sure what I can do with it in the nursing home, though.

It would mean that any device that uses electrical energy would be redesigned, for example, computers, stoves, kettles, fridges, air conditioners, and anything that has a motor and a battery.

 

It would mean that any device that uses electrical energy would be redesigned, for example, computers, stoves, kettles, fridges, air conditioners, and anything that has a motor and a battery.

with the exception of anything that now uses a switched-mode supply, such as computers, fridges, air-condtioners etc.

However, I would think it more likely that the higher voltage distribution would be converted to DC. In other words, DC would extend down from the the highest layer - international interconnects, to a few lower layers, and the final distribution (which is 11kV phase-to-phase in Britain) would remain AC, so that the local supply would remain AC allowing easier domestic fusing and switching.

 

You are thinking of industrial scale centralized fusion reactor.

I am envisioning decentralized shoe-box-sized power sources in every home.
Battery technology would be revolutionary. There would be a different kind of power supply much different from what we currently know as switched-mode power supply. Every portable gadget from a torch (flashlight) to a shaver, power drill, smart phone, would be redesigned to benefit for the new technology.

 

You are thinking of industrial scale centralized fusion reactor.

True. I am imagining that the new-fangled fusion reactor will create electricity thorugh a steam turbine the design of which doesn't differ much from Charles Parsons' design of 1884.
I am sure that the energy distribution companies with want to keep the consumer paying, and will lobby governments against any localised power generation, or alternatively, someone will be keeping supplies of deuterium under tight control.