Study On The Breakdown Characteristics Of Helium Under Cryogenic Temperature And Low Pressure

Electrical performance of insulating material under cryogenic temperature draws more attention as the development of superconducting and space technology,and it has been a critical factor of performance and reliability of cryogenic equipment.The cryogenic compressor in the superconducting device can be damaged and helium leakage accident may occur,and liquid helium as refrigerating medium can be vaporized into insulating system,which results in a low pressure condition,and may lead to breakdown of helium or flash over of solid in,sulating materials.Therefore,it is necessary to study the breakdown characteristics of helium under cryogenic temperature,and it not only can provide the reliability of superconducting device,but also provide test data for the insulating performance study under conditions with cryogenic temperature and vacuum/low pressure.Based on the insulation characteristic test system for gas in low temperature,electrode system which cannot be deformation or embrittlement under liquid helium temperature zone was designed for breakdown test under cryogenic temperature and low pressure.And the electrode system can measure the breakdown voltage of helium with high accuracy under cryogenic temperature.On the basis of this system,the helium strength was tested under 6.9K-300.0Kand the pressure range of 1.0Pa-1.0×105Pa.The helium strength was tested under cryogenic temperature and low pressure,and the main conclusions were as follows:(1)The breakdown voltage of helium which is within temperature from 6.9K to 300.0Kshows a descend trend followed by a ascend trend under the Pd which the product of pressure P and electrodes spacing d in the range of 1.0Pa·mm-1.0×105Pa·mm.There is a lowest breakdown voltage.(2)Within temperature from 6.9K to 300.OK,the lowest helium strength rise up and down,which reaches a highest value around 100.0K,and the lowest breakdown voltage at 6.9K is higher than that at 300.OK;(3)Within temperature from 6.9K to 300.0K,the Pd which corresponding to the lowest breakdown voltage is rise up with the temperature rising up.But the product of helium density ? and electrodes spacing S corresponding to the lowest breakdown voltage under different temperature are similar,and this shows that the ?S corresponding to the lowest breakdown voltage do not vary with temperature change.