Electrical insulation characteristics of liquid helium under high speed rotating field

Electrical breakdown behavior of liquid helium was investigated under high speed rotating field. In the development of superconducting turbine generators, it is essential to obtain knowledge of the electrical insulation characteristics of liquid helium under high speed rotating field. When the current of the field magnet of a superconducting generator is changed, changing magnetic field generates heat in the conductor and causes bubbles in the liquid helium around the conductor. The behavior of these bubbles is affected largely by the buoyancy which is generated by the centrifugal force. Electrical breakdown behavior of the liquid helium is strongly dependent on the gas bubbles in the liquid. The electrical breakdown voltage between electrodes was measured in a rotating cryostat with and without heater input for bubble formation. Reduction of the breakdown voltage by the heater power was smaller in a rotating field than that in a nonrotating field