Is household DC in our future?

psionl0 said:
Skin effect is an RF issue. It would be scarcely noticeable at 50-60 Hz.
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Skin depth at 60Hz is a little over half a centimeter. This increases the resistance of the transmission line enough to create losses over long distances.

psionl0 said:
And capacitance is not a loss since capacitors are energy storage devices.
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Energy is stored but that stored energy is then released to ground 60 times per second. Capacitance acts a little like a high impedance short to ground (or between the transmission lines). The charge on the line causes opposing charge to build up nearby and when the voltage changes on the line this charge bleeds away.
 
lomiller said:
Skin depth at 60Hz is a little over half a centimeter. This increases the resistance of the transmission line enough to create losses over long distances.



Energy is stored but that stored energy is then released to ground 60 times per second. Capacitance acts a little like a high impedance short to ground (or between the transmission lines). The charge on the line causes opposing charge to build up nearby and when the voltage changes on the line this charge bleeds away.
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:thumbsup:

Was working on a similar reply when this posted.
 
Ziggurat said:
You can't bury long-distance AC power lines underground, because the capacitance of the lines will be too large.
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With what undesired result?

Ziggurat said:
But the capacitance doesn't really matter for DC transmission, making buried DC lines possible.
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Neighborhoods in Germany have buried lines instead of overhead. There could be above-ground lines connecting a whole neighborhood's underground distribution point to the power source; I wouldn't recall whether I saw such lines or not anymore. Do you know whether this means Germany uses buried DC transmission the whole way, or chooses to accept whatever drawback long-distance underground AC has, or at some point close enough to the destination switches from overhead to underground? If the latter, I wonder what that maximum underground distance would be.
 
psionl0 said:
You have got to be joking!
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I was addressing the suggestion that DC to AC was hard, it’s not that hard. What’s hard is making it efficient and scaling up to the voltages/currents required for DC power transmission.

psionl0 said:
Sine wave inverters are a simple matter of electronics. They are used to convert the DC from solar panels to AC. Do you really think that solar penetration would be so widespread if the only thing that households could get from solar electricity was square wave mains?
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Your home solar system does not approach the efficiency of the converter stations used in HVDC transmission. Low power applications can get away with producing sin waves at the cost of efficiency. Larger power requires that the device be either on or off so it’s effectively acting as a switch. This produces wave forms with significant harmonics that must be dealt with.
 
psionl0 said:
Real world cables also have inductance which would tend to oppose the extra
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Inductive losses are along the line capacitive losses are between the lines, so no they don’t oppose each other.

psionl0 said:
The main problem with transmission lines is with reflections. In RF equipment, it is essential that you terminate your RF output into the correct impedance or you will get standing wave issues
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Power generation/transmission is not RF. Impedance matching trades power delivered to the load for efficiency. It’s efficiency that matters most in power systems.
 
Delvo said:
With what undesired result?
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In AC transmission capacitance acts a little like a high impedance short so you have a small current between the wires and each other and between the wires and ground. It’s tiny at any given location but adds up when the line is very long.

Changes in current though a wire a changing magnetic field around the wire. This induces voltages in nearby conductors which in turn create circulating currents. The energy to drive the currents comes from the magnetic field created by the current tough the wire. It’s basically the same principle as a transformer. The coupling is very weak so it only matters a lot over long distances and high power. Changes in voltage along the wire create a changing eclectic field this eclectic field pulls charge towards and away from the wire as the field changes.

In both cases the energy required to move the charge comes from the transmission line, leaching small amounts of power for every mile the electricity is transmitted. Both are zero at zero frequency and rise as frequency increases.
 
lomiller said:
Your home solar system does not approach the efficiency of the converter stations used in HVDC transmission. Low power applications can get away with producing sin waves at the cost of efficiency. Larger power requires that the device be either on or off so it’s effectively acting as a switch. This produces wave forms with significant harmonics that must be dealt with.
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Stop making things up!
 
psionl0 said:
Stop making things up!
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Yeah I’m the one “making stuff up” :rolleyes:
https://en.wikipedia.org/wiki/Transformer
Transformer energy losses are dominated by winding and core losses. Transformers' efficiency tends to improve with increasing transformer capacity. The efficiency of typical distribution transformers is between about 98 and 99 percent
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http://www.solar-facts.com/inverters/inverter-efficiency.php
Efficiency may vary from something just over 50% when a trickle of power is being used, to something over 90% when the output is approaching the inverters rated output.
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One thing that others haven't mentioned is arcing.

Once a DC arc starts, it is hard to stop.

I've heard stories of arcs burning cables all the way back to the battery (in off-grid DC homes).
 
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