Will AC power distribution become obsolete?

[coppice]

The 1930s radios that I have seen also used lacquer insulated power transformers, not much different to their 1950s successors,but it is possible  there were others that did not survive.

In the 1930s those transformers would have used some kind of traditional lacquer. By the 50s, and certainly the late 50s, they still called the stuff they used lacquer, but I think it was a product of the rapidly emerging polymers industry.

The only place I have seen beeswax is in inductors operating at much lower power levels & often higher frequencies.

I've seen old capacitors that had something looking like beeswax in them.

[David Hess]

What does a DC to DC converter for replacing a pole-pig transformer look like?  It has to step down say 2,400 volts to 240 volts with an output current of 200 amps.  A transformer to supply 10 homes costs $4,000 under normal conditions but $20,000 now because of a shortage.  Could you make that DC to DC converter for $400, or even $2000?

7200 volts is more typical these days. 4160 may still be around.

Ok, but the same question applies.  How much would a DC to DC converter at these voltages and power levels cost compared to the transformer it would replace?

The RMS voltage levels at input and output are roughly the same as the AC case with transformers because they come down to power delivered at a current that the cross section of the wires can support.

At 99% efficiency, it takes a long time to justify replacing 80 year old hardware with 99.5% efficient new.

I really doubt DC to DC converters at this power level will be as efficient as transformers.  It is hard enough getting to 95%, and resonate designs save in switching losses but don't they increase circulating current losses?  Trading a large expensive transformer for large high frequency capacitors, inductors, and transformers does not strike me as a cost saving measure.

[coppice]

At 99% efficiency, it takes a long time to justify replacing 80 year old hardware with 99.5% efficient new.

I really doubt DC to DC converters at this power level will be as efficient as transformers.  It is hard enough getting to 95%, and resonate designs save in switching losses but don't they increase circulating current losses?  Trading a large expensive transformer for large high frequency capacitors, inductors, and transformers does not strike me as a cost saving measure.

You can make now make highly efficient DC to DC converters of many sizes, but it costs significantly to get every last little scrap of further efficiency. This is why you'll see expensive high efficiency converters in things like cellular base stations, where they will be running at 3kW day and night, and they can earn back the additional cost from the saved energy. However, when your load is highly variable, and the average power is way below the maximum, people don't usually have an incentive to pay too much extra for the converter.

[T3sl4co1l]

Lacquers were pretty much the universal choice for power transformers, at least from the 1940s on, initially natural, but later artificial.
I have worked on TV broadcasting equipment from Marconi, made in the 1950s, & there was nary a sign of beeswax, rubber, or pitch in any of their power transformers.

The 1930s radios that I have seen also used lacquer insulated power transformers, not much different to their 1950s successors,but it is possible  there were others that did not survive.

The only place I have seen beeswax is in inductors operating at much lower power levels & often higher frequencies.

I recall once taking apart a ~300VA transformer from an organ, might've been '40s era, which was quite waxy inside.  Beeswax would fit.  No idea how prevalent that was though.  Not that I've taken apart many from that era, anyway, but it seems like some manner of lacquer/varnish was at least more common.

Pitch is often used for potting (even today I think, in specialty circles; though extremely messy, it is serviceable, it can be melted out), but I think not so much as impregnation for first-line insulation purposes.

Tim

[madires]

Are internet data centers powered with LV DC?

Some have a -48V DC power distribution to power critical network elements. It's basically used as a large online UPS. However, most stuff in data centers is powered by mains AC, in some cases HV DC. With today's power density requirements (kW per rack) a LV DC only data center would be insane.

[Zucca]

I've seen old capacitors that had something looking like beeswax in them.

https://www.dhtrob.com/projecten/elna1_en.php

[David Hess]

The low frequency systems were mainly for running large universal motors - AC so you could use transformers, but low frequency so that winding inductance didn't limit motor power, and as easily controlled as a DC motor in the pre-electronic era.

Easier to control because the field connection is separate from the rotor connection, so only a fraction of the current needs to be adjusted, and with AC, that can be done with transformers maintaining efficiency.  The only disadvantage is having brushes and a commutator which wear out.

My 1970s era sewing machine works that way for variable speed controlled with the foot pedal, with no semiconductor switching.

I remember retrofitting an old machine tool in the 1990s with variable speed electric drive, and even then a DC motor with wound field was the best option.  This was a big multi-horsepower motor.  Now I suspect an AC motor would be better because power and control electronics has improved so much since then.

[Xena E]

Thank you for your "corrections".

I'm not obviously as old as yourself and don't know the exact form of the Australian market at the time we are talking about. Also the comments were not directly specific to Australian TV production and I haven't been able to find evidence of legislation in Australia that ever suggested there was a ban on AC/DC equipment.

The evidence is that European manufacturers decided that the saving of a few coins were worth the exclusion of the transformer in these designs, over and above any perceived safety considerations.

Also I didnt say that there were any pitch, or, wax impregnated transformers made in Australia, but these did exist in other areas of the world markets, and I'm doubtful that it was not the case in Australian manufacturers output, synthetic insulation is a relatively recent introduction worldwide, early 1950's onwards perhaps. Naturally occurring lacquers rubber, beeswax and pitch were the only material available historically.

Again I'm sorry for any offence caused, it was only a commentary on the techniques used based on evidence of historical designs, not a slight on the choices of Australian manufacturing materials or practices.

No offence, but some of the material purporting to be historically correct needs to be taken with "a grain of salt".

Lacquers were pretty much the universal choice for power transformers, at least from the 1940s on, initially natural, but later artificial.
I have worked on TV broadcasting equipment from Marconi, made in the 1950s, & there was nary a sign of beeswax, rubber, or pitch in any of their power transformers.

The 1930s radios that I have seen also used lacquer insulated power transformers, not much different to their 1950s successors,but it is possible  there were others that did not survive.

The only place I have seen beeswax is in inductors operating at much lower power levels & often higher frequencies.

Thank you for this.

Natural shellac was not particularly durable, (hence potting in wax, or pitch also done for mechanical stability) nitrocellulose is a low order explosive, and also toxic so it wasn't ever really a good follow on to shellac. When it caught fire it did properly, and the fumes were unpleasant at least.

Both were usually preserved and fixed with wax or pitch as the lacquers were often viewed as too expensive for impregnation... the TV and radio industries in Europe and the UK weren't protected against imports, costs were cut and so was quality in a lot of instances.

Things did get better with the introduction of polyurethane enamelled finishes but that was all 50's onwards.

I really can't comment on Marconi transmitting equipment as I have no experience, it obviously had to be built to a much higher standard, but consumer equipment having waxed craft paper interwinding insulation in transformers I have: in some instances in equipment that was so produced as late as the latter 1960's. A hybrid SABA CTV frame scan output choke I had rewound for a vintage TV enthusiast as a favour was probably polyurethane wire enamel but its mechanical potting was definitely craftpaper/beeswax.

You would be quite correct saying that I don't  know fuck all much about the Australian electronics industry but it seems that you seem to think my comments were all directed at Aussie consumer electronics policies and production methods, which it was not.

You commented:

...some of the material purporting to be historically correct needs to be taken with "a grain of salt"...

Quite so! So why then post this?

One exception was Ekco, who unsuccessfully linked up with Oz firm AEI to build & sell both TVs & AM Broadcasts Radios in the Australian market,during that brief foray adopting the local standard transformer-type architecture in both cases.

The early EKCO sets made by AEI all had live chassis.
Here's an Australian POV on the question...

https://www.cool386.com/ekco_tcx298/ekco_tcx298.html

Regards,
Xena.

[IanB]

but consumer equipment having waxed craft paper interwinding insulation in transformers I have: in some instances in equipment that was so produced as late as the latter 1960's. A hybrid SABA CTV frame scan output choke I had rewound for a vintage TV enthusiast as a favour was probably polyurethane wire enamel but its mechanical potting was definitely craftpaper/beeswax.

I had big transformers scavenged in the 70's from decades old radio equipment. I liked how much current I could get from the filament windings and I used to overload them regularly. When they got hot they started hissing and fizzing. Maybe that's a sign of wax impregnation? I don't know if I would want to power them up today, I don't know how safe they would be.

[T3sl4co1l]

Varnish has been around for a long time: https://en.wikipedia.org/wiki/Alkyd

You'd have to look up typical materials at the time, but it was likely in use back in those days.  Natural materials might've been chosen for familiarity, ease of use, reduced cost, known properties, etc.  Polyurethane (colloquial "varnish" today) is a more modern take on it.

Tim

[paulca]

There is concern with the future "momentum" involved in the grid.  The momentum which is required to self regulate the AC frequency and the response to the same which loads and unloads gen sets and therefore turbines to maintain the frequency.

Solar produces zero momentum, although arguably their generated pilot wave may count as artificial synchronisation.

I don't know if wind turbines use synchronous 3 phase motors and only engage when the rotor is in sync or if they use AC-DC-AC synchro. 

The point is, none of these alt renewables asides hydro/tidal involve massive spinning 1000 ton axles and turbine cores.

If when the grid is trying to run on a sunny, windy day, entirely without fossil fuels then who regulates the frequency and how?  Do we have master phase inducers?  What?  How does the grid detect demand?  Voltage drop?  Currently if there is more demand than production the millions of tons of turbines start slowing down.  Automatically another will begin receiving steam to take up the deficit and fix the frequency.

AC-DC-AC links are used all over europe to get around the awkwardness of having to synchronise between grids to trade power. 

[Someone]

If when the grid is trying to run on a sunny, windy day, entirely without fossil fuels then who regulates the frequency and how?

Given batteries with inverters are making a killing doing frequency control, that's already been passed over as a "problem". Its mainstream already:
https://www.aemo.com.au/-/media/Files/Electricity/NEM/Security_and_Reliability/Ancillary_Services/Battery-Energy-Storage-System-requirements-for-contingency-FCAS-registration.pdf
Solar, Wind, and anything else with DC-AC inverters or frequency agility can provide almost arbitrary virtual inertia.... if they are permitted to.

[Andy Chee]

If when the grid is trying to run on a sunny, windy day, entirely without fossil fuels then who regulates the frequency and how?

Solar, Wind, and anything else with DC-AC inverters or frequency agility can provide almost arbitrary virtual inertia.... if they are permitted to.

"Virtual" inertia is not the same as real rotational inertia.

It's analogous to the difference between an opamp gyrator simulated inductor and a true coil inductor.

https://sound-au.com/articles/gyrator-filters.htm

A gyrator cannot store energy, whilst a true coil inductor can.

Similarly, rotational inertia of a massive turbine wheel is better suited to grid stability than battery powered inverters. 

In that respect, energy storage in a flywheel would be better than energy storage in battery chemistry.

Alternatively, as the thread title suggests, a DC grid wouldn't need such rotational inertia.  Batteries and capacitors can be connected directly to the DC grid (via appropriate switchgear and protection) and would provide the necessary "DC momentum".

[coppice]

If when the grid is trying to run on a sunny, windy day, entirely without fossil fuels then who regulates the frequency and how?

Given batteries with inverters are making a killing doing frequency control, that's already been passed over as a "problem". Its mainstream already:
https://www.aemo.com.au/-/media/Files/Electricity/NEM/Security_and_Reliability/Ancillary_Services/Battery-Energy-Storage-System-requirements-for-contingency-FCAS-registration.pdf
Solar, Wind, and anything else with DC-AC inverters or frequency agility can provide almost arbitrary virtual inertia.... if they are permitted to.

That is centralised control. I think paulca was referring to the problem of achieving control with a million tiny and weakly regulated energy sources.

[David Hess]

Solar produces zero momentum, although arguably their generated pilot wave may count as artificial synchronisation.

Nothing prevents inverters from implementing frequency control with "virtual inertia" except their power capability.  They do not have the massive peak power capability which automatically comes with big polyphase alternators; it has to be designed in which adds cost.

I don't know if wind turbines use synchronous 3 phase motors and only engage when the rotor is in sync or if they use AC-DC-AC synchro.

I thought they commonly used a doubly fed induction generator.  This is an alternator but with a 3 phase input to drive the field, so the rotor RPM can vary while producing a constant and controlled output frequency and power.  So these also can push the grid frequency.

If when the grid is trying to run on a sunny, windy day, entirely without fossil fuels then who regulates the frequency and how?  Do we have master phase inducers?  What?  How does the grid detect demand?  Voltage drop?  Currently if there is more demand than production the millions of tons of turbines start slowing down.  Automatically another will begin receiving steam to take up the deficit and fix the frequency.

Inverters can push and pull the grid frequency now if designed to, and a quartz crystal frequency reference is good enough.  Some inverters push the frequency higher deliberately, within the limit, to deliver more power when the grid voltage is already at maximum.

"Virtual" inertia is not the same as real rotational inertia.

It's analogous to the difference between an opamp gyrator simulated inductor and a true coil inductor.

That is a great example of the difference.

A gyrator cannot store energy, whilst a true coil inductor can.

Similarly, rotational inertia of a massive turbine wheel is better suited to grid stability than battery powered inverters.

Nothing prevents making a "power gyrator".  Buffer the output of the operational amplifier with the power amplifier that can provide the required current and voltage.  The problem is that it is more difficult to scale electronics up in power than an alternator which only requires more copper wire and steel.

In that respect, energy storage in a flywheel would be better than energy storage in battery chemistry.

But flywheels lack the energy storage of batteries.

Even on the old electric grid, flywheels are sometimes added in the form of synchronous condensers which are used as massive adjustable capacitors to correct the power factor of inductive loads.

[richard.cs]

I don't know if wind turbines use synchronous 3 phase motors and only engage when the rotor is in sync or if they use AC-DC-AC synchro.

I thought they commonly used a doubly fed induction generator.  This is an alternator but with a 3 phase input to drive the field, so the rotor RPM can vary while producing a constant and controlled output frequency and power.  So these also can push the grid frequency.

I think they used to, but certainly the modern off-shore turbines around the UK use a DC connection to the shore. Poor inverter config contributed to grid problems on 2019-08-19. See the section on Hornsea 1 here: https://www.ofgem.gov.uk/sites/default/files/docs/2020/01/9_august_2019_power_outage_report.pdf

[hneve]

While it could simplify things in homes and sync better with renewables, AC's widespread infrastructure and historical use still make it practical for now.

[Marco]

I think paulca was referring to the problem of achieving control with a million tiny and weakly regulated energy sources.

It's easier.

To combat undesired grid currents from rooftop PV now, their control is switching taps ... mechanical (if they can do that under load, if not retrofitting something with equivalent effect is a PITA). With unregulated sources on LVDC, the bidirectional LVDC<->MVDC switcher can just allow the LVDC voltage to rise electronically if they don't want the currents on the grid.

[Andy Chee]

Nothing prevents making a "power gyrator".  Buffer the output of the operational amplifier with the power amplifier that can provide the required current and voltage.

But can a gyrator replace the inductor in a buck/boost converter?  This is essentially the energy storage analogy I was going for.

Similarly, flywheels and/or turbines can provide grid inertia that inverters cannot supply.

But flywheels lack the energy storage of batteries.

A flywheel need not be equal energy capacity and completely substitute a battery.  The flywheel merely behaves as a capacitor on the AC output of the inverter (as opposed to a capacitor on the DC input side of the inverter).

[Marco]

Similarly, flywheels and/or turbines can provide grid inertia that inverters cannot supply.

Battery inverters can catch up to demand increase in microseconds, there is no need for inertia beyond the distributed capacitance.

[Someone]

If when the grid is trying to run on a sunny, windy day, entirely without fossil fuels then who regulates the frequency and how?

Solar, Wind, and anything else with DC-AC inverters or frequency agility can provide almost arbitrary virtual inertia.... if they are permitted to.

"Virtual" inertia is not the same as real rotational inertia.

It's analogous to the difference between an opamp gyrator simulated inductor and a true coil inductor.

https://sound-au.com/articles/gyrator-filters.htm

A gyrator cannot store energy, whilst a true coil inductor can.

Similarly, rotational inertia of a massive turbine wheel is better suited to grid stability than battery powered inverters.

Not equivalent at all, I'm talking about devices that DO have energy storage and can act as 4 quadrant power devices. Virtual inertia works fine.

[Someone]

If when the grid is trying to run on a sunny, windy day, entirely without fossil fuels then who regulates the frequency and how?

Given batteries with inverters are making a killing doing frequency control, that's already been passed over as a "problem". Its mainstream already:
https://www.aemo.com.au/-/media/Files/Electricity/NEM/Security_and_Reliability/Ancillary_Services/Battery-Energy-Storage-System-requirements-for-contingency-FCAS-registration.pdf
Solar, Wind, and anything else with DC-AC inverters or frequency agility can provide almost arbitrary virtual inertia.... if they are permitted to.

That is centralised control. I think paulca was referring to the problem of achieving control with a million tiny and weakly regulated energy sources.

Distributed control is feasible and already demonstrated in smaller grids. Why are large "centralised" sources essential?

[Andy Chee]

Similarly, flywheels and/or turbines can provide grid inertia that inverters cannot supply.

Battery inverters can catch up to demand increase in microseconds, there is no need for inertia beyond the distributed capacitance.

"Catching up to demand" is frequency agility, but I'm talking about frequency stiffness.  They are two different concepts.

If an inverter is going to chase and follow every fluctuation that happens on the grid as loads are turned on and off, that does NOT make for a stable grid. 

Imagine if that fluctuation frequency becomes resonant somewhere in the grid.  You're going to get blown transformers or circuit protection tripping all over the place.

[Marco]

If an inverter is going to chase and follow every fluctuation that happens on the grid as loads are turned on and off, that does NOT make for a stable grid. 

The inverter algorithm can try to maintain the sine and its amplitude as stiff or loosely as you want up to its maximum output. There are no magic inertia watts, there is voltage and current. It puts current into output to try to create a voltage ... if you really want you can make a near perfect facsimile to the rotating mass in software.

Imagine if that fluctuation frequency becomes resonant somewhere in the grid.

Imagine if even mechanical systems could resonate ...

[IanB]

Surely the point is that electricity grids are very large dynamic systems. I know of people who do grid modeling, and I understand it is very complex. On a grid scale, something that fluctuates in one place will not have its effect felt immediately a thousand miles away. So two things trying to control the grid frequency simultaneously on opposite sides of the grid could end up fighting each other.

The inverter algorithm can try to maintain the sine and its amplitude as stiff or loosely as you want up to its maximum output. There are no magic inertia watts, there is voltage and current. It puts current into output to try to create a voltage ... if you really want you can make a near perfect facsimile to the rotating mass in software.

Perhaps, but what is the "maximum output"? What if it is hundreds of megawatts? Can a software emulation source or sink that amount of power?