Design and Testing of a Gas-Helium Conduction Cooled REBCO Magnet for a 300 kvar HTS Synchronous Condenser Prototype

A 300 kvar high temperature superconducting synchronous condenser is under construction. In this work, a test superconducting magnet consisting of two double-pancake coils was designed, fabricated and tested. The coils had an effective length of 300 mm. They were wound by 5 mm wide REBCO tapes and vacuum impregnated by paraffin. The test magnet was cooled by a distributed-tubes-inside-pancakes conduction cooling structure. In this structure, 20 K helium gas was forced to flow in the tubes which were embedded in stainless-steel cover plates of coils. The magnet was installed in a vacuum chamber for cooling and transport tests. The results showed that the magnet was effectively cooled to about 22 K and operated stably at 281 A. The magnet steady-state temperatures at different operation current were recorded, approximately 2 K higher than the helium gas. Moreover, the thermal stability of the magnet was evaluated by adjusting inlet gas temperature from around 20 K to 25 K, and no magnet quench was observed. It was concluded that the cooling structure of the test magnet could fulfill the requirements of the 300 kvar HTS synchronous condenser.