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IIR document

Cooling unit for superconducting electricity cables.

Number: pap. n. 65

Author(s) : HERZOG F., KUTZ T.

Summary

High temperature super conductors (HTS) lose their electrical resistance at temperatures close to the boiling point of liquid nitrogen (77 K). Therefore it is possible to design very efficient liquid nitrogen operated cooling systems for this kind of superconductor installations. The critical current of superconducting electrical power cables increases when the operating temperature is reduced. So it is desirable to operate these cables even below 77 K (-196°C). To achieve such low temperatures liquid nitrogen has to be vaporized below atmospheric pressure. Messer has developed a cooling unit which makes use of this physical effect. The unit is designed for a vaporizing pressure of 150 mbar. At this pressure the boiling temperature of nitrogen is 64 K (-209°C). Lower temperatures are not practical, because at 63 K (-210°C) nitrogen becomes solid. Main components of the cooling unit are a liquid nitrogen circulation system, a vacuum subcooler and a storage vessel. Liquid nitrogen is circulated through the superconducting cable to take out the heat there and afterwards it is pumped through the subcooler to be recooled. In the circulation system liquid nitrogen is only used as a heat transfer medium, it stays always liquid (subcooled) and does not vaporize. On the secondary side of the subcooler liquid nitrogen from the storage vessel is used as refrigerant. Here it is vaporized under vacuum conditions to achieve the desired low temperatures. The cooling unit was delivered in 2013 for the AmpaCity-project of RWE Deutschland AG. Within this project RWE and Nexans installed the worldwide longest superconducting power cable in the city of Essen, Germany. It cools a 10 kV HTS cable with a length of 1.000 m developed and manufactured by Nexans.

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Pages: 99-104

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Details

  • Original title: Cooling unit for superconducting electricity cables.
  • Record ID : 30011071
  • Languages: English
  • Source: Cryogenics 2014. Proceedings of the 13th IIR International Conference: Prague, Czech Republic, April 7-11, 2014.
  • Publication date: 2014/04/07

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