A HTS SYNCHRONOUS MOTOR AT DIFFERENT OPERATING TEMPERATURES

A four pole synchronous machine comprising HTS racetrack field winding s has been designed and constructed. The device has been investigated at 4.2 K, 77 K and at the nominal operating temperature 20 K. The nomi nal power of 1500 W was achieved at a speed of 1500 rpm and an excitat ion current of 205 A. The field coils provided expected performance. T he transition between the superconducting and the normal state took pl ace gradually both at 77 K and 4.2 K, operation remained stable althou gh the voltage was clearly I ising. Stability performance of HTS magne ts differs strongly fi om their LTS counterparts. The normal zone prop agation velocity is roughly 20 times higher at liquid helium temperatu res than at 77 K. These questions will be briefly addressed in this pa per, along with a discussion of test result.