Superconductor Power Lines

Randall Parker at FuturePundit has a post on superconducting power cables, in which he notes their benefits over copper:

Superconductor power cables can carry three to five times the power of conventional copper cables. Compact, underground superconductor cables can be used to expand capacity and direct power flows at strategic points on the electric power grid and can be used in city centers where there is enormous demand, but little space under the streets for additional copper cables.

High-temperature superconductor technology is also being used in transformers, to great effect. The company mentioned in Randall’s post, American Superconductor, is doing pioneering work in this field, and has run some successful pilots with Detroit Power & Light. Another important feature of HTS that Randall didn’t mention is that they have no line loss, unlike copper cables (power loss increases with the square of distance traveled, in copper cables), so that means less total power generation to get a given amount of power delivered from A to B.

What, you mean technological change promotes energy conservation? I’m shocked, shocked to hear that! (note: heavy sarcasm)

2 thoughts on “Superconductor Power Lines

  1. No line loss! That would’ve been considered a miracle 100 years ago!

    I don’t have time to read details, but does this mean that with this technology DC current is just feasible as AC?

  2. It is incorrect to say that superconducting power lines have “zero losses:” They simply have no “I^2 R” losses. However, in conformity with the Second Law of Thermodynamics, they _do_ have other types of losses!

    Even the so-called “High Temperature” superconductors must _still_ be refrigerated to cryogenic temperatures — they simply don’t need to be kept _quite_ as cold as “ordinary” superconductors [on the order of liquid nitrogen temperatures (77.36 Kelvin / -195.79 C / -320.42 F) rather than liquid helium temperatures (4.22 K / -268.93 C / -452.07 F)]. Despite advances in thermal insulation, the Second Law of Thermodynamics dictates that it is PHYSICALLY IMPOSSIBLE to create a _perfect_ thermal insulator, so heat will _always_ leak into the cryogenic line — and by Carnot’s Theorem, it will always take at _least_ (T_hot-T_cold)/T_cold watts of refrigeration power to pump each watt of heat leakage back out of the line. Since the environmental environmental temperature T_hot is around 300 K, that means that even a _perfect_ refrigerator would consume almost 3 watts of power per every watt of heat that leaks into the superconducting line. Furthermore, since the amount of leak that leaks into the line will to a first approximation be proportional to its length, we are still talking about an _effective_ “line loss” proportional to the length of the line. This _effective_ line loss will not show up as a “voltage drop,” since superconductors have zero D.C. resistance; however, if one makes the reasonable assumption that the line will be tapped for the power required to refrigerate itself, this parasitic refrigeration load will act as a non-zero _current_ loss per unit length — i.e., an effective “shunt” impedance.

    Also, please note that superconductors are only “perfect” conductors of _D.C._ current: Their A.C. resistance is non-zero, and increases with frequency. Moreover, superconducting power lines are no more immune to the problem of “impedance matching” than any other electrical device — and since the effective line impedance is low, superconducting lines will need to be supplied with low-voltage, high-current power. Hence, for superconducting transmission, it will be necessary to convert high-voltage A.C. to low-voltage high-current D.C. at the supply end, and re-convert to high-voltage low current A.C. for local distribution at the demand end — and each of these conversion steps are less than 100% efficient, and will therefore incur losses.

    Superconductors are a useful technology — but they are =NOT= “magic,” and they are =NOT= a panacea. One must always keep in mind the Seventh Corollary of Murphy’s Law: Every “solution” will create _new problems_…

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