Design Of The Current Leads And Research On The Service Test Procedures For Superconducting Power Devices

The study of service test procedures and design of current leads for superconducting power devices are two important aspects in superconducting power technology. The standardization of service test procedures can help to promote the technical advantage and reliability of the superconducting power devices, and it is necessary to accelerate superconducting power manufactures to go on the market. Current leads are often the major heat link to the low-temperature level of cryogenic systems and cause the main part of the boil-off of the cryogenic liquids or the power consumption of the cryocoolers. Therefore, the standardization of the service test procedures and the design of the current leads are centered about in this paper.In the aspect of design of current leads, firstly, the conceptual models of heat load for all-metal current leads and hybrid current leads are conceived, respectively. Secondly, based on the finite element method and heat transfer theory, their low-temperature heat load is analyzed and simulated. Furthermore, considering the dynamic case motion and cooling system of the superconducting power devices, the suitable type of the current leads are brought forward. Thirdly, after the operating condition, insulation level and technics characteristics have been investigated, the current leads for 300kVA high temperature superconducting transformer are optimized. According to the room limitation of the electrical colomotive, a method of prolonging of the path for heat transfer is put forward. Then, a simple test set for heat leakage to liquid nitrogen is desiged and fabricated, and a series of experiments are carried out on measuring the gas flux respectively. The experimental results show a good accordance with the simulation, which show that the unitary helical current lead meets the requirements of design. In order to choose tectorial mode and moulding technics for insulating materials covered on the current leads, a cooling experiment is done in advance and a feasible scheme is determined. Lastly, the current leads are carried to completion.A heat transfoer model of the hybrid current lead for cryocooler conduction-cooled high temperature magnetic energe storage system (H-Tc SMES) is schemed to calculate the low-temperature heat load. The current lead consists of three modules. This kind of structure is used to facilitate its design, fabrication and test in division form. According to the requirements for different modules, the current lead is optilized. At first, the minimam heat leakage values for three different metal matirals are calculated and judged. After that, copper is choosed for the metal module. The optimum heat leakage value of a copper current lead is 41.7W/kA which is almost equal to that of 42W/kA of the conduction-cooled case calculated by Hull, but, it is slightly lower than that of 47W/kA obtained by Wilson in 1983. At second, a structure for electrical insulation and thermal conduction is designed, and, the thermal contact resistance and heat leakage of AlN undertaking the work for electrical insulation and thermal conduction. Furthermore, the radiant heat of H-Tc SMES is figured. Based on these above, the electric power consumption of the cryocooler for this case is obtained. Finally, the temperature profiles, such as lead temperature during cooling down, temperature variation of the lead during DC excitation, temperature variation of the lead during different current slopes, temperature of dynamic experiments, are shown and analysed.In order to know the serviceability of AlN after laser drilling, its insulating strength and thermal conductivity are studied. According to the infuences of laser drilling on the hole-surface of AlN in the thermal conductivity, a concept of three areas is put forward. The relationship among the contents of Al and Al2O3 on the surface of hole, their distributions and insulation level is illustrated. Then, the suitable laser cutting velocity is represented.In the aspect of design of the service test procedures for superconducting power devieds, based on the electromagnetic characteristic, the test items of superconducting magnetic energy storage systems, superconducting fault current limiters, superconducting cables and superconducting transformers are studied and generalized. This work fills a blank in power application on superconductivity in China.