Development and testing of joints in high temperature superconducting power cable

The development of long length HTS power cables require joints between HTS tapes and former, HTS cable and current leads of termination units, and also between two separate HTS cables. These joints should offer minimum electrical resistance which is the fundamental need for power transmission using superconductors. This paper explains the jointing techniques utilized in the setup for India’s first seven-meter-long HTS power cable rated at 11 kV and 1 kA. Initially, the joints between the HTS cables and that between the cable and current leads were produced using simple soldering method with low temperature solder materials. However, this resulted in an increase in the net circuit resistance (6 mΩ) and undesirable boil-offs while operation of the cable. The issue was resolved by using HTS jumper tapes across the joint, thus bringing the net circuit resistance to within 0.1 mΩ and observable reduction in boil-off, increasing the duration of experiment from 170 minutes to 240 minutes for the same volume of LN₂ used.