High Temperature Superconductors Wires And Cables: Technologies Of Energy Conservation

Emerging technologies of High Temperature Superconductors (HTSrs) have an enormous potential for improving capacity of underground and overhead power T&D systems, motors, generators and power plants – because higher Jc and zero resistance of HTSrs reduce losses and can replace conventional conductors... - Hambir Singh

Rapidly growing population, industrialisation, urbanisation, smart cities and transportation have led to rising demand for the electric power supply through T&D cables and wires. Demand of energy for world’s economy is consuming colossal fossil fuels (such as coal, petroleum oil and NG) in the electricity generation and transportation – and it is being forecasted by EIA that electricity generation may be doubled to 30673.8 TKWhr by 2030 from the 16595.2 TKWhr (2004), which will damage the whole ecological balance. So, energy conservation by the energy efficient winding wires and power    T&D system is essential to solve the problem of energy shortage, depletion of fossil fuels and environmental crisis (pollution and electromagnetic radiation). Power T&D cable networks are the backbone of the economic growth. Near about 8% electrical energy is being lost due to technical reasons. Technical losses in conventional power T&D systems are due to conventional conductors (Such as Al & Cu), which are used in the winding of cables, generators, overhead lines, motors and transformers. Due to the characteristic conditions of conventional conductors, power T&D cables and wires wear low critical current density (Jc) (Table 1) and they experience a drop in voltage and dissipate lot of the electrical power in the form of joule heat (I2R). As, transformers’ failure due to poor efficiency of conventional conductors lost about 400 million kWh energy/year according to National Committee on Distribution 1995. Emerging technologies of High Temperature Superconductors (HTSrs) have an enormous potential for significantly improving capacity of underground and overhead power T&D systems, motors, generators and power plants – because higher Jc and zero resistance of HTSrs reduce losses and can replace conventional conductors and low temperature superconductor (LTSrs) also. Therefore, in the present energy and environmental crisis, selection of energy efficient winding wires and power T & D cable technologies is essential to increase efficiency of the whole power industry and demand side. This article explains that how technologies of HTSrs eliminate shortcomings of power T&D systems and power generation industries for energy conservation.

High temperature superconductors

In 1986, HTSr (LaBaCuO) discovered at 350K (the phenomenon of disappearing of electrical resistance of superconducting materials at high Tc). In March 1987, High Temperature Superconductivity (HTSy) in YBaCuO compound was also discovered at 930K as the compound cooled by LN2 (770K). Thereafter, many discovered compounds (like YBaCuO, BiSrCaCuO, MgB2, HgBaCaCuO and TlBaCaCuO) have been fabricated for commercial applications, which are highly effective in power cables and wires compared to conventional conductors and liquid helium (LHe, 4.20K) cooled LTSrs (like Nb3Sn, NbTi etc). Since the discovery of HTSy, superconductivity in many superconducting materials has been reported above the room temperature (RT>≥300 K). First generation (BiSrCaCuO) and second generation (YBaCuO) of HTSrs are giving higher level of energy efficiency improvements in the electricity generations, nanotechnology, magnetic refrigeration, transportation, medical care (MRI, CT Scan etc., as detecting of small magnetic field by HT SQUIDs), windmill direct drive generator, tokomak, power grids and demand side power utilisations (Figure 1). Generally, identifying factors for superconductivity are zero electrical resistance below Tc, Hc & Jc and complete absence of internal magnetic field in the metals or compounds (When a material makes the transition from the normal to superconducting state, it actively excludes magnetic fields from its interior; this is called the Meissner Effect); above these parameters property of superconductivity vanishes. High temperature superconducting (HTSing) wire works efficiently to carry large Jc at very high Hc or self-field along with high Tc (Table 1 & 2) which are giving opportunities to develop highly energy efficient wires, tape and thin film and help to reduce environmental pollutants as well as GHGs (Such as CO2, NOx, CH4, SF6 etc). Wires of HTSrs are resistance free under bath of LN2 (coolant) and can wear Jc 100-150 times the amount of same size conventional conductors. In the USA, inefficient conventional power generation process and T&D system waste about 400 million barrels oil/year according to PSFC Massachusetts Institute of Technology (USA). AC and DC power cables of HTSrs offer a highly desirable alternative to conventional wires and cables. Losses of electricity and natural resources in the conventional electrical designs are due to conventional conductor’s lower Jc & Tc and high resistance.

Fig. 1: Projected demand of HTSrs in the different sectors…
(Source: HT Baiej, University of Wollongong, Thesis collection, 2013).

Characteristics properties of HTSrs

Perfect superconductors work efficiently under the limits of some critical parameters or in the superconducting state [Tc, Jc, Hc/ or (HC1 & HC2)], beyond these parameters any superconducting materials may be found fail to perform efficiently in applications.

  • Transition Temperature (Tc): The temperature below which, metals or materials completely lose their electrical resistance.
  • Critical Current Density (Jc): Jc of the conductors depends on the density of electrons in their unit volume. Superconductors/ HTSrs allow flow of electric power under zero voltage drops in the superconducting state. However, beyond critical limits of Jc, superconductors develop resistance and property of superconductivity ceases.
  • Critical Magnetic Field (Hc): Superconductivity in metals or materials can be destroyed by the applied strong external magnetic field (H) when applied H in the superconducting state exceeds a critical value (Hc) and it depends on the function of temperature of operation (T <Tc) also.

HTSrs winding wires and power T&D cable

Energy conservation targets and environmental challenges can be solved by the HTSrs wires and cables technologies instead of conventional conductors (Figure 2). Wires and thin film of HTSrs are highly capable to wear large Jc (> 106 amp/cm2 at 770K) with zero resistance, low impedance, zero electromagnetic radiation and free from hazardous cooling oil than conventional power cables and wires. Underground power T&D network of HT Superconducting technology uses inexpensive and environmentally safe LN2 cooling core, which maintain superconducting state of materials. In addition, installation costs of underground T & D cable could be cut more than 20%. Reliability of electrical cables, tapes and wires is almost dependent upon the selection of conductors and their thermal, mechanical and electrical properties. DC power transmission through HTSrs has absolutely zero resistance or zero electrical losses. HTSing cable losses are less than half (4%) compared to 8% of conventional power cables; and losses in the power industries and utilities can be avoided up to 90% (Table 3). Power transmission cable losses are about 2.5% of total transmitted power while the losses in transformers are between 1 and 2%. It is being expected by the scientists of the USA that technologies of HTSrs could save more than 10774 GWhr of energy and 1638940 metric tons carbon, 16891 metric tons SOx and 8351 metric tons NOx by 2025. In conventional overhead Cu based power T&D cable system, about 740 kW/km of electrical energy is dissipated due to high resistance of conductor that can be reduced by HTSrs (Table 2). Transmission of 5 GW with 765 kV overhead AC lines require about 600′ wide Right of Way (ROW) & 130′ high and heavy pole; whereas 5GW with 200 kV underground DC cables of HTSrs require about 3’diameter pipe and 25′ ROW according to AMSC (USA) that avoid complex, contentious and costly procedures (Figure 3).

Fig. 2: Energy conservation potential (%) in the different sectors of India…

Advantages of HTSing power T&D cables and wires

HTSrs based energy efficient technologies are capable to provide energy conservation and environmental advantages:-

  • HTSrs with LN2 dielectric extend operating life of cables, wire and insulation.
  • Needs about 25% ROW compared to conventional conductor.
  • Increased resources security and clean energy production.
  • HTSrs cooling with LN2 will replace oil cooled transformers and power T&D system.
  • Enhance energy efficiency of electricity generation.
  • Replacement of costly and environmentally unsafe SF6 (it has the highest global warming potential 23600) and LHe by LN2 at the power grid sgas transmission cables, energy storage devices etc.
  • HTSing cables have no external magnetic fields radiation due to self-shielding design that eliminates the impact on living beings.
  • 2nd and 3rd generation HTSr Reduce cable & wire size, weight and production cost.

Fig. 3: Comparison of HTSrs and conventional power T&D systems…(Source: AMSC USA).

Conclusion

In 21st Century, Technologies of HTSrs are opening new horizons for energy efficiency improvements and energy conservation efforts. The applicable ability of HTSrs with zero resistance can make many revolutions in the electricity generation, utilities, power cables, wires and many other fields. I predicts that in near future room temperature superconductor will serve in commercial applications.
Growing demand of energy and environmental crisis are forcing to develop and discover energy efficient and clean power generation technology. It is being concluded in this article that emerging power cable and wire technology of HTSrs are giving better opportunities to operational flexibility, energy conservation and environmental pollution and GHGs emissions reduction.


Do you think in near future room temperature superconductor will serve in commercial applications? Yes or no? Comment your answer now!

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