Development of a 1250-kVA Superconducting Transformer and Its Demonstration at the Superconducting Substation

A three-phase 1250-kVA/10.5-kV/0.4-kV hightemperature superconducting (HTS) transformer has been designed and fabricated. The windings of the HTS transformer are wound by copper-alloy-reinforced multifilamentary Bi2223/Ag tapes, and the structures of the primary and secondary windings are solenoid and double pancake, respectively. The three-phase three-limb core is made of domain-refined high-induction-type grain-oriented silicon sheet steel, and the cryostat is made of glass-fiber-reinforced plastics. According to the tests, the no-load loss is 2319.2 W at an exciting current of 0.254% of the rated level, the short-circuit impedance of the transformer is 5.6% of the rated value, and the average load loss is 249.6 W. In addition, the leakage current between the primary and secondary windings is about 12.6 mA under the condition of 35 kV/1 min/50 Hz, and the negative full-wave lighting impulse test with a peak voltage of 75 kV/1.0 μs/50 μs from the primary winding is carried out without breakdown. The experimental results show that the developed HTS transformer meets the requirements of the Chinese standards, and the demonstration of the HTS transformer at the superconducting power substation since September 9, 2014 has been reliable, showing its potential for long-term operation in the grid.