If we could change grids in one way, the best thing we could probably do is switch from HVAC for transmission to HVDC.

I think the ideal grid would switch from DC to AC either at a substation at central location for a community.

Why might someone do this?

One of the hardest problems to work through is a grid cold start. When a grid goes completely down it takes a monumental effort to bring it back up again. There's a delicate balance that has to be struck with load and other generators coming online. It's hard to do. The AC waveform is a finicky thing that gets pulled and mutilated by every motor or vacuum cleaner that starts running.

With a bunch of AC microgrids joined by a DC major grid, you can completely sidestep that problem. It suddenly becomes just a lot easier to ramp up power production because the deformations to the waveform happen in small local regions, not everywhere in the grid. And further, the other plants just have to watch the DC voltage, they don't need a whole bunch of equipment around syncing with the AC waveform of the grid as a whole.

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jacquesm 36 minutes ago | parent | next [-]

> With a bunch of AC microgrids joined by a DC major grid, you can completely sidestep that problem.

Not necessarily. Big local consumers will be large relative to the microgrid, which will not have a lot inertia. This is one of the things that you really notice when you go 'off grid', your grid is essentially your house and whatever else you decide to power from it and unless there are a couple of beefy motors already running starting a new one has a high likelihood of tripping the inverter, even a very beefy one. Start-up currents for larger consumers can be really high and you need a lot of inertia in your grid to overcome that.

	▲	cogman10 6 minutes ago \| parent [-]
		> Start-up currents for larger consumers can be really high and you need a lot of inertia in your grid to overcome that. This is true of an AC grid as well. Big inductive loads will often have to buy special equipment before hooking up to the grid because of their impact. It'd be the same with a DC first grid. To overcome a large startup current they'd likely need to buy a bunch of capacitors. Which, funnily, is exactly what they'd have to do to run on straight AC.

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Waterluvian an hour ago | parent | prev [-]

I grew up understanding that one of Tesla’s big innovations was using AC to transmit power distances so that there weren’t tremendous losses and line meltings or something. Can someone help me reconcile the delta between this understanding and the above comment? Was this not actually a thing? Or have we overcome it somehow?

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jacquesm 33 minutes ago | parent [-]

HVDC is a miracle of modern engineering that could not have been done in the days of Tesla. It removes several sources of losses that otherwise would have turned valuable power into heat. That said, it isn't without drawbacks: the cables are quite expensive, harder to repair and somewhat fragile, and 'local stepdown' which otherwise would just be a properly rated (capacity and insulation) transformer now turns into a much higher technology exercise. HVDC is for now relegated to a long haul role not unlike oil pipelines compared to the AC network which is far more interconnected and wide spread. You are unlikely to see HVDC used for lower level distribution in the next decade, just as you are unlikely to see your local gas station hooked up to an oil pipeline.

	▲	cogman10 2 minutes ago \| parent [-]
		> the cables are quite expensive, harder to repair and somewhat fragile Nope, HVDC uses the same style of cable as AC. I'm not sure why you'd think they'd be different. The HVDC cables that can be expensive are meant to be submerged. A feat that only HVDC can do. HVAC can't be submerged due to the capacative effect. But otherwise I agree. It's more a pipedream for me that HVDC becomes more common place as I believe it'd make grids ultimately more stable and resilient.