Will AC power distribution become obsolete?

[johansen]

On the other hand on a long enough timeline on a DC microgrid it might make sense to drop to 48V at the socket so most appliances become SELV. DC-DC buck is cheap and reliable, electrolytics are an AC problem.

Will you pay for replacing the mains wiring in all buildings worldwide with new wires with five times the cross section? Copper is expensive! And remodeling buildings too.

Yeah to suggest we will have 48v dc in the home is insanity and never going to happen.

What I do expect in my lifetime is a power cost and availability crisis which will result in all of your larger power consuming devices to be controlled in a negotiated handshake with the power grid.

[vk6zgo]

Let’s not forget that it was only a few years ago that the last remnants of the DC grid in New York City were shut down. The remaining DC customers had to get rectifier units installed.

Those final DC customers included high-power DC motors (easily controlled) used for elevators and similar applications.
75 years ago or so, some New York residents had to use "AC-DC" radios (with tube half-wave rectifiers that could pass DC without transformers) because of DC distribution.
That led to a now-obsolete form of jokes about AC or DC in other unrelated topics.

AC-DC radios  which, as their name suggests, can operate on ac or DC mains, were widespread across North America & Europe during the 1950s/'60s, mainly, in the NA case because the manufacturers could save a few cents on power transformers.
In Europe it was mainly because of the still relatively common use of DC mains, especially in mining towns.

Looking at pre WW2 US radios, they mostly used transformers, with AC/DC much less prevalent.(radios were also quite expensive, so the relatively small cost of a power transformer was of minor concern.

In Australia, the situation was quite different, as the massive ramping up of tube construction during WW2 was all aimed at 6.3 volt & 12 volt heater types as used in the majority of military equipment.

This left the tube makers with a large inventory of such types & setting up new production lines for series string heater types was not viable, so they had to be imported.
DC mains supplies, though still not unusual, were scattered, appearing in smaller communities, the power grid was not well established, & any new installations were going to be ac.

On top of that, in Australia, radios had always been costly, transformers were relatively cheap, the Electrical regulators did not like the idea of transformerless designs in the least, so that country went for the power transformer/full wave rectifier architecture.

There are a number of advantages with such designs apart from using 6v heater tubes, such as full wave rectification requires less filtering, the mains are isolated from the chassis so you don't need elaborate insulation, you can have any HT voltage you can get transformer secondaries wound for, meaning audio output stages are capable of greater power. (this is a drawback for transformerless designs on "110v" systems, though not so much with 220/240v)

[vk6zgo]

But why?

Why is telecom -48V? Distribution because silicon is cheaper than copper/cabling. Microgrids because of SELV, renewable power, batteries and EVs.

DC will ingress regardless, if it manages to ingress far enough that keeping AC in the middle stops making sense, you slowly switch over. Over a long enough timeline it could happen, though I don't think there is any likely long timeline without apocalyptic change.

-48v DC is a legacy of many years before the mains grid became established, when telegraph & telephone systems were already becoming widespread.

With single conductor earth return telegraph systems there was always a corrosion problem with the earth return connection.
It was found this could be minimised by using the battery positive to earth.

The telegraph & phone were unaffected by this, so it became the standard.

[vk6zgo]

That change is simple:  all passenger vehicles switch on Saturday, and commercial vehicles switch on the next day Sunday.

Yep. Switching from left hand side to right hand side has been done before in other countries. Tesla is no longer making right-hand-side drive versions of some of their models. Other car manufacturers may follow. So the idea of needing to switch from left side driving to right side driving may not be that far fetched.

I really doubt that Japan or India are going to change anytime soon.

[Xena E]

But why? For changes sake? Or to appease the criminally stupid in society?

Why is telecom -48V? Distribution because silicon is cheaper than copper/cabling. Microgrids because of SELV, renewable power, batteries and EVs.

Those comments just dont make any sense.

DC will ingress regardless, if it manages to ingress far enough that keeping AC in the middle stops making sense, you slowly switch over. Over a long enough timeline it could happen, though I don't think there is any likely long timeline without apocalyptic change.

That's just proliferation of complexity and unreliability, there will be MORE AC links, not less, in the form of unavoidably less reliable buck/boost DC converversion. They will still contain transformers.

DC at any given voltage is more problematic:

It is more dangerous, not only shocks, but also safe disconnection can be problematic with sustained arcing, degraded switchgear and corroded connections.

Leave DC distribution to long distance point to point where it is viable.

The best way to be sound ecologically speaking is not to dump a whole infrastructure

Concentrate on moving away from fossil fuel sources sure. But don't change the electricity supply industry when it's not needed because a few febrile minded snowflakes think its a good idea.

[Marco]

That's just proliferation of complexity and unreliability

In the future generators will be the only pure AC motors left, we're getting close to begin with. More of the distribution will be HVDC too with inherently DC generating power sources (ie. solar, battery and fuel cells). The 50 Hz AC in the middle is then the one causing complexity and unreliability ... the inverters are there any way, but they have to deal with the incredibly awkward 50 Hz AC.

Leave DC distribution to long distance point to point where it is viable.

Industry will want it too, if you're driving large loads with an inverter 50 Hz AC is a PITA, moreso than needing better contactors and fuses. Datacenters would also rather not have to deal with AC and power factor.

So what remains is domestic ... government could decide to put new large building projects on 350V DC microgrids and require high power appliances to be rated for DC drive (minimal changes required) and just use inverters where AC is still needed. A slow erosion of AC.

[johansen]

You must have no idea that half of the power grid demand is 60hz induction motors larger than 100hp.

And if the cost savings of running such motors on a vfd dont pay for the vfd in 3 years.. they dont install them.

[themadhippy]

You must have no idea that half of the power grid demand is 60hz induction motors larger than 100hp.

I recon its a safe bet that our grid hasn't many  60hz induction motors connected directly to it

[DavidAlfa]

  The primary benefit of HVDC is in the transmission e.g. no capacitive loss, no skin effect,

Skin effect at 50/60Hz? 

To me, the problem is mainly the capacitance.
Imagine a very long wire making 1uF, that's 2.6Kohm @ 60Hz.
Not a big deal at 110 or 240V, and might be even a good thing, compensating the power factor.
But at 100KV, 500KV, the currents will get huge.

DC would only make sense in the HV side, that's why it's used in marine lines, capacitance gets really large.

[Marco]

And if the cost savings of running such motors on a vfd dont pay for the vfd in 3 years.. they dont install them.

Then they have to decide how to pay for power factor too, one way or another they will.

[Andy Chee]

You must have no idea that half of the power grid demand is 60hz induction motors larger than 100hp.

I recon its a safe bet that our grid hasn't many  60hz induction motors connected directly to it

Does a generator being backfed by the grid count? 

(TLDW; internal power failures to the control circuits meant the generator could not be disconnected from the grid, resulting in the generator becoming a motor, and then exploding from overspeed/loss of lubrication)

[johansen]

And if the cost savings of running such motors on a vfd dont pay for the vfd in 3 years.. they dont install them.

Then they have to decide how to pay for power factor too, one way or another they will.

The cost to mitigate the power factor is the lifecycle cost of very low loss self healing metalized film capacitors. - almost negligible. Seriously, on the order of 1 watt losses per kva and a dollar a year to replace the capacitor.

The cost of a vfd? An igbt block every 20 years and capacitors every 5 to 10 years. Control board every 10 years due to rats and mice and random failures. You do the math. And they are only 98% efficient, driving a 97 to 99%% efficient motor.

Vfds are a step backwards unless the efficiency improvements of variable speed pay for themselves.

Regarding power factor.. usually you dont get charged for power factor if its greater than 90%, which motors over 100hp usually are.
Friend of mine has a 40 grand a month power bill and his excess kva charge is usually 100$ a month. His powerfactor is over 90% but not during plant startups where the 15min demand charge is excessive, and there is a 500$ demand charge added to his bill.

Its.. actually not worth the time and energy to reduce said bill.

The load is almost entirely 20 to 100hp motors

[johansen]

You must have no idea that half of the power grid demand is 60hz induction motors larger than 100hp.

I recon its a safe bet that our grid hasn't many  60hz induction motors connected directly to it

What industry is left in your country?

[AVGresponding]

Yeah to suggest we will have 48v dc in the home is insanity and never going to happen.

What I do expect in my lifetime is a power cost and availability crisis which will result in all of your larger power consuming devices to be controlled in a negotiated handshake with the power grid.

Bollocks to that! When I want a cup of tea, I'm switching on my 3kW kettle and I damn well expect boiling water in a couple of minutes as a result!

And if the cost savings of running such motors on a vfd dont pay for the vfd in 3 years.. they dont install them.

Then they have to decide how to pay for power factor too, one way or another they will.

Large commercial and industrial users are already charged for this, hence their use of large PFC and voltage optimisers, as well as VFDs for anything bigger than a couple of hundred watts.

One of our buildings runs entirely (every light and every socket, every appliance) through a large UPS, which has the same effect.

[soldar]

You must have no idea that half of the power grid demand is 60hz induction motors larger than 100hp.

I recon its a safe bet that our grid hasn't many  60hz induction motors connected directly to it

Don't be silly. I think its a safe bet he means 50/60 Hz, whatever each country has.

[Monkeh]

You must have no idea that half of the power grid demand is 60hz induction motors larger than 100hp.

I recon its a safe bet that our grid hasn't many  60hz induction motors connected directly to it

What industry is left in your country?

None at 60Hz. Like the majority of the planet.

[soldar]

Will AC power distribution become obsolete?

No. I cannot say "never" because it would run afoul of the Rule Against Perpetuities so I will state that it will not become obsolete before 21 years after the last of all the posters in this thread has died. You can all rest easy now.



https://www.merriam-webster.com/legal/rule%20against%20perpetuities

rule against perpetuities: a common-law rule stating that in order for a future interest to be good it must vest after its creation (as at the death of a testator) within a life in being or lives in being plus 21 years plus the period of gestation of any beneficiary conceived but not yet born

[Xena E]

That's just proliferation of complexity and unreliability

In the future generators will be the only pure AC motors left, we're getting close to begin with. More of the distribution will be HVDC too with inherently DC generating power sources (ie. solar, battery and fuel cells). The 50 Hz AC in the middle is then the one causing complexity and unreliability ... the inverters are there any way, but they have to deal with the incredibly awkward 50 Hz AC.

Leave DC distribution to long distance point to point where it is viable.

Industry will want it too, if you're driving large loads with an inverter 50 Hz AC is a PITA, moreso than needing better contactors and fuses. Datacenters would also rather not have to deal with AC and power factor.

So what remains is domestic ... government could decide to put new large building projects on 350V DC microgrids and require high power appliances to be rated for DC drive (minimal changes required) and just use inverters where AC is still needed. A slow erosion of AC.

Well... you seem to be sold on this.
I guess you have some vested interest ?

... in the future...

What are you, a prophet, or politico, you're certainly not an EE.

I'd just like to know how all this magic is going to happen... detail how it's going to be done: Don't make assertions without knowledge.

And I for one don't want 350VDC anywhere near my home.

I recently had a similar discussion with a political canvaser:

Ecological topics:

First talking about DC mains, Why? Renewable energy is the most important issue.

They spouted nonsensical pseudo technical claims, on safety, ecology, efficiency. All false.

I mentioned that without some form of AC link technology the DC would have to be generated and distributed at final voltage level requiring impractical cable sizing.

Oh no, the canvasser said, it will all be done by high power wireless links and "clever level conversion equipment"

like DC charge pumps? I asked...

Yes exactly! They said.

I wonder if it makes these people sad that they are so fucking stupid.

I don't think so, they don't realise they are stupid.

[nctnico]

  The primary benefit of HVDC is in the transmission e.g. no capacitive loss, no skin effect,

Skin effect at 50/60Hz? 

Yes. Skin effect is a function of cross section and frequency which goes down all the way to DC.

[T3sl4co1l]

  The primary benefit of HVDC is in the transmission e.g. no capacitive loss, no skin effect,

Skin effect at 50/60Hz? 

Yes. Skin effect is a function of cross section and frequency which goes down all the way to DC.

Specifically, for Cu at mains frequency, it's a few cm dia -- enough that #4-0 is about as large as you want to go, and indeed you get into parallel wires (depending on code) or bus bars by then.

HVDC lines aren't usually that much bigger, actually; the current is kept around a kA, just the voltage is raised so much to transmit lots of power.  Does mean they don't have to space them out, and can just use bigger builds.  Though there might still be reason to use the same style anyway: a wider effective conductor to reduce corona or abrasion due to wind movement, or using nominal size cables because they're what's available.

Tim

[themadhippy]

enough that #4-0 is about as large as you want to go, and indeed you get into parallel wires (depending on code) or bus bars by then.

Thats about 105mm² if im reading the tables correct,not that big , unless you haven't played  with many large installations.

[pcprogrammer]

Another reason why a single low voltage DC net in your house is not feasible.

The transition to heat pumps that has started. With the high powers needed to heat your house running it of 30VDC is not a good idea. At minimum 1KW for a very small house with high startup currents because the compressor is a heavy load, you can see your cables go up in smoke if they are not big enough.

Oh no, the canvasser said, it will all be done by high power wireless links and "clever level conversion equipment"

That is what we get from all the idiots on the internet. 

[David Hess]

AC-DC radios  which, as their name suggests, can operate on ac or DC mains, were widespread across North America & Europe during the 1950s/'60s, mainly, in the NA case because the manufacturers could save a few cents on power transformers.
In Europe it was mainly because of the still relatively common use of DC mains, especially in mining towns.

Looking at pre WW2 US radios, they mostly used transformers, with AC/DC much less prevalent.(radios were also quite expensive, so the relatively small cost of a power transformer was of minor concern.

In Australia, the situation was quite different, as the massive ramping up of tube construction during WW2 was all aimed at 6.3 volt & 12 volt heater types as used in the majority of military equipment.

This left the tube makers with a large inventory of such types & setting up new production lines for series string heater types was not viable, so they had to be imported.
DC mains supplies, though still not unusual, were scattered, appearing in smaller communities, the power grid was not well established, & any new installations were going to be ac.

On top of that, in Australia, radios had always been costly, transformers were relatively cheap, the Electrical regulators did not like the idea of transformerless designs in the least, so that country went for the power transformer/full wave rectifier architecture.

There are a number of advantages with such designs apart from using 6v heater tubes, such as full wave rectification requires less filtering, the mains are isolated from the chassis so you don't need elaborate insulation, you can have any HT voltage you can get transformer secondaries wound for, meaning audio output stages are capable of greater power. (this is a drawback for transformerless designs on "110v" systems, though not so much with 220/240v)

The radios were called the All American Five:

https://en.wikipedia.org/wiki/All_American_Five

The tube filaments all drew the same current, with different voltages, so they could be wired in series and run directly from 120 volts AC or DC.

[soldar]

The radios were called the All American Five:

https://en.wikipedia.org/wiki/All_American_Five

The tube filaments all drew the same current, with different voltages, so they could be wired in series and run directly from 120 volts AC or DC.

They were also common in Europe and the first radio receivers that I built myself were of this type.

[IanB]

The tube filaments all drew the same current, with different voltages, so they could be wired in series and run directly from 120 volts AC or DC.

Televisions in the UK all used to be constructed this way. As a child I used to scavenge old equipment for power transformers, and I soon learned that TV sets did not have transformers inside them, even though they had many valves (vacuum tubes). They also had a huge wire wound power resistor to use a voltage divider. That thing was mounted in free air not touching anything because it got very hot in use.