Breakdown and Flashover Properties of Cryogenic Liquid Fuel for Superconducting Energy Pipeline

The cooling of cryogenic liquid fuel in a superconducting cable is an important technical means to realize efficient energy and power transmission. However, there are only few types of cryogenic liquid fuels that can maintain the superconducting strip below the critical temperature, and little is known about the insulating properties of fuels other than liquid hydrogen. Besides, cryogenic liquid fuels are flammable and explosive, and a safe operating procedure is essential to conduct the discharge tests. Based on the trinitrotoluene equivalent method, the safety distance of the discharge test is determined, and the safety precautions are summarized in this article. Taking the molar ratio of methane to propane as 3:1, the breakdown and flashover voltages of liquefied small molecular alkanes were studied, and the test of long-time withstand voltage was also carried out. At last, the discharge parameters and waveform, as well as the surface state of the polymer after flashover in the fuel, were analyzed. The breakdown field strength of cryogenic liquid fuel is 22.9 kV/mm, and the flashover field strength is 15.9 kV/mm. The reduction of breakdown strength is not found in the test of long-time withstand voltage. Therefore, it has some advantages for the liquid fuels to directly cool the superconducting strips from the cost and electrical performance. This study aims at the superconducting energy pipeline cooling by liquefied natural gas, and it can also provide technical references for the electrical property and safety research of other fuels.