Development of Joint Technology on Superconducting Cables for Feeder

Electric railways have several problems due to electrical resistance of feeder lines such as a transmission loss and a voltage drop. In order to solve these problems, we have been developing superconducting feeder cable, which enables zero-resistance power transmission. Now we have been able to obtain government approval to conduct commercial operation using superconducting cables. It has been begun the commercial operations on passengers using superconducting cable for railway. One of the challenges of the superconducting feeder cable is its joining technique. To introduce superconducting feeder cable between substations, it is required to join superconducting feeder cable to each other at a railway site. First, we conducted an internal observation of the superconducting solder joint using X-ray CT and evaluated the state of the joint. It was found that joining under pressure is effective in reducing joint resistance. Therefore, we performed simple pressure joining using a tweezers-type soldering iron so that it could be performed at railway sites, and evaluated the current characteristics. Joining using this method yielded a low joint resistance on the order of 10
⁻¹¹
Ω·m
²
, and was found to be effective for joining at railway sites. These results give standards of the joining of superconducting feeder cable.