I am aware of industry looking at High Voltage DC transmission lines in two distinct areas: Underseas transportation to islands or between continents and for long distance coupling of distribution nets.
The reasons for DC are rather simple and that is that when the transmission line length becomes relatively long in comparison to the wavelength of the AC then it may start acting as antenna instead of transmission line and if the capacitance becomes significant (which cannot be avoided in underseas transport, in contrast to open lines in the air) then the losses of an AC line become so large that it makes sense to go through the hassle of converting the AC to DC, transport it without the associated capacitance or radiating losses and then convert back to AC. Added benefit of DC and the separate conversions from/to AC is that you don't care about synchronising the two grids that you connect, you simply transport current through the DC line in either direction and the two grids can be at different frequency, phase or voltage, it does not matter. Today east coast and west coast USA are unconnected, the plans to do so are using DC lines for all the reasons mentioned before. Obviously disconnecting a high voltage DC line is an issue, but so is a high voltage AC line since it does not matter that the voltage and current goes through zero - once a plasma path in air is created by the initial arc, it will continue to conduct until the line is disconnected successfully elsewhere, no matter if it is AC or DC. Cor van de Water Chief Scientist Proxim Wireless office +1 408 383 7626 Skype: cor_van_de_water XoIP +31 87 784 1130 private: cvandewater.info http://www.proxim.com This email message (including any attachments) contains confidential and proprietary information of Proxim Wireless Corporation. If you received this message in error, please delete it and notify the sender. Any unauthorized use, disclosure, distribution, or copying of any part of this message is prohibited. -----Original Message----- From: EV [mailto:[email protected]] On Behalf Of Peri Hartman via EV Sent: Wednesday, June 08, 2016 12:07 PM To: Robert Bruninga; Electric Vehicle Discussion List Subject: Re: [EVDL] Off-grid solar house and electric car charging Robert, I'm not sure how much effect the Skin Effect has. But for #2, peak power losses, you also need to consider that part of the wave form is *below* the average voltage, thus contributing significantly *less* resistance. You can't just look at the resistance caused by the peak voltage. Thirdly, you note that the industry is looking seriously at a DC-based grid. Do you have any references that claim the reason behind this is because of line loss due to resistance? Or is it for other reasons? Even it it is line loss - and this is where Skin Effect may play an important role - 1MV is way different than 220V. Peri ------ Original Message ------ From: "Robert Bruninga via EV" <[email protected]> To: "Electric Vehicle Discussion List" <[email protected]> Sent: 08-Jun-16 11:53:51 AM Subject: Re: [EVDL] Off-grid solar house and electric car charging >Im sorry again, but this is simply not true when expanded to WIRE LOSS. > >> No; AC voltages and currents... (Root-Mean-Square). >> RMS voltages and currents have the *same* effective >> values, voltage drops, and losses as DC. 120vac and >> 120vdc are completely equivalent. > >Yes, as far as VOLTS and as AMPS as averages are concerned. Such as >average power. A 1500W resistor will be 1500W whether on DC or RMS AC. > >But the power loss in wires feeding that resistor will have greater >loss >on AC because of two factors important in distribution systems: > >1) SKIN EFFECT where the AC current is pushed to the outside of the >wire >so that not all the wire is carrying the same current. Thus the wire >is >not as effective since not all of its copper is being used in an AC >system > >2) Peak power losses. As you note, the RMS current is the same, but >the >PEAK current is 1.4 times higher during the peak of the waveform and >since >that is where the most power is delivered that is also where the most >loss >occurs in the wire. So the average power lost in the wire for AC is >almost twice (1.4 squared) the loss in the same wire at DC. > >Google it... > >That is why the entire industry is looking at DC transmission lines now >that we are finally getting to the point where the up and down >conversion >is becomming cost competitive with transformers... > >Bob >-----Original Message----- >From: EV [mailto:[email protected]] On Behalf Of Lee Hart via >EV >Sent: Wednesday, June 08, 2016 2:03 PM >To: Electric Vehicle Discussion List >Subject: Re: [EVDL] Off-grid solar house and electric car charging > >Robert Bruninga via EV wrote: >> Still not true. The output of microinverters is at 240 VAC and the >> average current in the wires will be double as the same number of >>panels >at 480 VDC. > >But each microinverter has its own wire. The total current may be twice >as >much in a 240v system as in a 480v system; but there are twice the >number >of wires, each half the size. You wind up back where you started. > >> Further, AC peak currents are 1.4 times higher than DC so the peak >> currents (where the losses are) are 2.8 times greater > >No; AC voltages and currents are normally expressed in RMS >(Root-Mean-Square). RMS voltages and currents have the *same* effective >values, voltage drops, and losses as DC. 120vac and 120vdc are >completely >equivalent. > >> The difference in buying #6 wire instead of #12 is only $180 versus >> $30. Or you can ignore the extra 10% or so losses and use #10 wire. >> But over the life of the system (20 years) the losses in your solar >> system can add up to many thousands of dollars. > >Sure; it's basically an economic decision. How much can you afford >up-front, to reduce long-term losses? It's further complicated because >when you eventually scrap the system, much of the cost of the copper is >recoverable. > >Note that this is the EV discussion list. Besides these tradeoffs, >weight >is also an issue. You may be ahead by deliberately undersizing the wire >to >save weight. The benefit from weight reduction can exceed the >efficiency >loss. Racers know this well! > >> Maybe I am just being nitpicky, but my solar arrays are all over my >> yard and house. Some runs are over 300 feet! (shortest is maybe >>60'). > >Ah; no wonder you are so concerned with wire lengths. I definitely >consider 60-300 feet *long* runs! The PV panels on my house are only >20' >from my circuit breaker panel. > >-- >"IC chip performance doubles every 18 months." -- Moore's law "The >speed >of software halves every 18 months." -- Gates' law >-- >Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com >_______________________________________________ >UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub >http://lists.evdl.org/listinfo.cgi/ev-evdl.org >Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag >racing at NEDRA (http://groups.yahoo.com/group/NEDRA) >_______________________________________________ >UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub >http://lists.evdl.org/listinfo.cgi/ev-evdl.org >Read EVAngel's EV News at http://evdl.org/evln/ >Please discuss EV drag racing at NEDRA >(http://groups.yahoo.com/group/NEDRA) > > _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
