The objective of this demonstration is to check the availability of a high-temperature superconducting power distribution system for low-voltage, high-current power direct-current interior wiring for usage such as data center or other technical building. To enhance the installation flexibility of the system in restricted spaces, Sumitomo Electric has downsized the cables, related equipment and devices, and also developed a new splitter box to branch a superconducting cable.
During the demonstration, Sumitomo Electric will check the reliability of the equipment and the entire system, as well as the feasibility of the method used for installing the superconducting cable along a vertical path of 18 m and the stability of the cooling system for vertically installed cable.
1. Outline of the System
This system consists of two superconducting cables (each 35 m long), a splitter box outdoor sealing ends that connect the superconducting cables to the existing power cables, cryogenic cooling system for liquid nitrogen circulation which cools these equipment and devices down, and an operation monitoring system.
2. System Components
- (1) High-temperature superconducting cable (3.3 kV AC, line current rating of 210 A, 1.2 MVA)
- The cable is a three-core in one cryostat type cable with a reduced diameter (outside diameter: approx. 100 mm) comprising a total length of 6 km of bismuth-based high-temperature superconducting wires, “DI-BSCCO Type ACT-CA,” made by Sumitomo Electric.
A high-temperature superconducting wire has no transmission loss when carrying a DC current, but has an insignificantly small loss when carrying an AC current. At present, Sumitomo Electric produces and sells six types of DI-BSCCO superconducting wires to meet various user needs. The Type ACT-CA wire is a thin, high-temperature superconducting wire (2.8 mm wide, 0.31 mm thick) that was developed to meet customer needs for supplying power to AC equipment with low power loss.
- (2) Splitter box and Outdoor Sealing end
- The outdoor sealing ends connect both ends of each superconducting cable to the existing power (normal conductor) grid. These joints are designed to minimize electrical resistance and prevent the penetration of heat between the superconducting cable and the existing power cable to maintain the superconducting cable at approximately -200°C.
In the past superconducting cable projects, Sumitomo Electric tested power transmission between limited two points. However, in data centers and other technical buildings, it is required to draw some of the power from a midway point along the transmission line. The splitter box is used for such purposes. In other words, the splitter box branches a cable into two or more directions while allowing the cable to transmit power at a temperature of -200°C. In this demonstration, the splitter boxes is not used for branching the cables but is used for changing the direction of power transmission.
- (3) Cooling system
- Liquid nitrogen is cooled to approximately -200°C by two 1 kW-capacity refrigerators and is supplied into the superconducting cables through the outdoor sealing ends. The liquid nitrogen is circulated through the cables to maintain the entire system in a superconducting state.
The two refrigerators are operated alternately to ensure trouble-free, long-term operation of the system. One of the refrigerators operates while the other is down for maintenance.
- (4) Operation monitoring system
- The monitoring system continuously monitors the overall system, and acquires and stores the performance data. When an abnormality in the system occurs, it will be immediately substituted to another power grid.
3. Future Plans
During the long-term (open-ended) demonstration operation, Sumitomo Electric will collect and analyze the performance data to study the optimum way to maintain the system. Sumitomo Densetsu Co., Ltd., which has an extensive experience in cable water/air cooling systems and group company of Sumitomo Electric, will cooperate to establish a maintenance system that can quickly cope in emergency situations.
High-temperature superconducting cable systems are expected to be a solution for transmitting and distributing electric power with low loss. Through the long-term demonstration of this system, Sumitomo Electric will continue to improve its superconductive products and maintenance system so that customers can use it reliably for a long period of time.
・“DI-BSCCO” is a trademark or registered trademark of Sumitomo Electric Industries, Ltd.