The Turbo-Brayton refrigerator generates cold by four processes:
1. Adiabatic compression
2. Isobaric cooling
3. Adiabatic expansion
4. Isobaric heating
The neon gas that is compressed by the turbo compressor ejects the compression heat to the atmosphere, then it is expanded under adiabatic condition by a turbo expander to lower the temperature of the neon gas. After that, it absorbs the surrounding heat and it is returned to the inlet of the turbo compressor. In case of an actual refrigerator, a heat exchanger is inserted between the turbo compressor and the turbo expander to collect the cold generated at the expander.
The temperature of the liquid nitrogen (LN2) at the outlet of the refrigerator is 70K (-203oC). The refrigeration capability is 10kW.
TNSC installed a NeoKelvin®-Turbo 10 kW prototype and contributed to successful trials in a proof of concept for a long distance superconducting power cable conducted by Korea Electric Power Corporation and LS Cable & System Ltd. at Jeju island, South Korea.
These results were highly regarded and the decision was made to adopt a NeoKelvin®-Turbo 10 kW for a commercial superconducting electricity transmission project. The unit has been installed at a transformer substation in Suwon, South Korea, and onsite test operation of the refrigerator section has now been completed.
The super conducting cable to be cooled by the unit – voltage 23 kV, electricity transmission capacity 50 MVA, length 1 km – will be installed between transformer substations within Suwon, and test operation and power transmission using the system is scheduled to begin in 2019.
Trial testing of superconducting electricity transmission cables and consideration for introduction are expected to proceed in South Korea and other countries around the world. TNSC will use its experience in this project to advance initiatives for capturing further orders going forward.