Cryogenic liquids-a prospective insulation basis for future power equipment

Cryogenic liquids are claimed to have a noteworthy impact on the concept of improved future power equipment. The low boiling temperature of liquid helium or liquid nitrogen offers the use of superconducting materials which eliminate ohmic losses in the conductors on the one hand. This yields a high overall current density in the equipment. On the other hand, the liquids seem to be interesting basic insulators with reasonable dielectric performance. The liquids are chemically inert, and no irreversible compound within the insulation system must be anticipated. Hazards such as fire risk in case of faults can be ruled out. Thermal aging of the insulation system can also be disregarded because no excess temperature must be taken into account during service, even in case of temporary overload operation. Dielectric aging due to partial discharges may be of little concern because the liquids can be easily fully reprocessed by vaporizing and recondensing in a closed cooling circuit; no memory effects then can degrade the liquid. Finally, the liquids are produced from gases which are found in open atmosphere. Thus, the disposal of insulation systems at the end of operational life is straightforward.