Brads Electronic Projects Forum

What is HVDC energy?

https://en.wikipedia.org/wiki/High-volt ... ct_current

Germany Takes the Lead in HVDC

http://spectrum.ieee.org/energy/renewab ... ad-in-hvdc

I'm wondering what this would do to our everyday electronics should we change.

I was always under the impression that AC was somewhat more efficient to transfer over long distances. However it does make sense that there would be huge losses due to the capacitance in the line having to charge and discharge. You would also get some sort of hysteresis losses due to the ever changing magnetic field in the transmission line. Perhaps the original reason that we transfer power via AC is because it is much easier to generate AC than it is DC.

AC incurs losses by transmitting off the lines, partly into space, partly into the ground; and the skin effect also keeps you from being able to use the whole conductor on big conductors, resulting in higher resistance for a given large wire size. However, there's no such thing as a DC transformer. To go to a different voltage, you have to have something like a switching regulator or a motor-generator (a motor driving a generator). The biggest switching regulators I believe I've heard of are used on locomotives. Motor-generators are far less efficient and don't last as long, at least not without maintenance.

I grew up in a country that used 230V 50Hz. The electrical code was probably more lax and not enforced well, and floors were usually concrete tile which is never fully dry, which means if you stand with bare feet and touch something that's 230VAC off of ground, you completed a circuit, and it was no fun. When I was a child, I did that, reaching into a lamp shade to turn on the lamp. It bit hard!!!! it was common to get shocked. I'm sure poorer countries go for the higher voltage so they can economize on wire size. On frequency, there's the trade-off in that lower frequency means less loss for carrying the power a given distance, but the transformers have to be bigger and more expensive.

When I was in college in 1978 (here in the States), the teacher said the worst frequency for your heart is 60Hz, and if you do it right, you can kill yourself with as little as 60V. So when they were choosing the line voltage and frequency in the US, they chose the worst frequency, and doubled the voltage just to be sure.

I didn't even think about skin effect, although how much would you get at such low frequencies? I know this is a huge problem for co-axial cables when you go into the multiple Ghz range though.

I also completely neglected the fact that we are constantly stepping up or down the voltage as it goes through the grid and on to our electronic devices and that does become a great deal more complex when dealing with DC.

Australia has twice the voltage as you guys in the USA but only 10Hz less frequency!

At 60Hz in copper, skin depth is just over a quarter inch, actually about 8.5mm. That's not an issue for something like #12 wire, but it becomes very significant for the huge wires used for hundreds of amps or more.

It seems then that skin effect must be working on a logarithmic scale with skin effect increasing quite dramatically at low frequencies and then perhaps tapering off?

The Wikipedia article has a good explanation and the equations for it.

Thank you Garth!