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GIL system: The main components of a GIL are an aluminum alloy casing and aluminum alloy conductors; both are mechanical products for which the manufacturing processes are relatively well-developed. SF6 insulating gas is a very stable and reliable insulating medium, and its properties are easy to measure. The epoxy casting process is also relatively mature at present, allowing for consistent control over product quality. Most of the work for GIL is completed in the factory, reducing many uncontrollable factors on site. The current-carrying capacity of a cable refers to the amount of current it can carry when installed in air, under the best cooling conditions; this capacity is lower in other installation scenarios. At present, the maximum cross-sectional area of cables is 2500 mm2; attempting to increase this area further would pose significant challenges in terms of manufacturing processes and transportation, and it would also affect the stability of product quality. In contrast, GIL systems can typically operate at full capacity, well above the current-carrying capacity of cables; therefore, GILs have a clear advantage in this regard. The transmission capacity of one GIL is equivalent to that of three cables. The cost comparison of 220 kV GILs and XLPE polyethylene cables is as follows: As can be seen from the table above, the total cost of the GILs, in terms of the price of the product itself, is only 75% of that of XLPE polyethylene cables. For the same transmission capacity, the costs at 500 kV are similar. Economic benefits of applying GIL ● High current-carrying capacity, which allows for a reduction in the number of transmission circuits in power plants and substations, thereby lowering overall costs ； ●It can address the spatial location constraints in some specific areas, as well as the issue of not being able to use overhead lines ； ●A design service life of 50 years ensures reliable operation, which far exceeds the expected lifespan of cable accessories and helps reduce overall costs ； ●The losses are much lower than those of cables and overhead lines, resulting in cumulative economic benefits ； ●The laying method is flexible and convenient, thereby allowing the reduction of line distances and cutting costs related to civil works and mechanical/electrical installations ； ●The individual pipeline units are long, and most of the work can be carried out in the factory, resulting in a short installation period and reduced costs for installation and commissioning ； ●It requires minimal maintenance and repair, offers high reliability, and effectively improves the availability of power plants and substations. Comparison of GIL and GIS structures: The GIL is equivalent to a longer GIS busbar, and its structure is much simpler than that of GIS. Due to its longer length, the GIL has its own characteristics regarding the factors that affect product quality: 1. Thermal expansion and contraction are key factors affecting the reliable operation of the product ； 2. The cumulative increase in machining accuracy errors and assembly errors must be effectively controlled ； 3. Difficulties in treating and cleaning the inner surface of the tube body ； 4. The on-site installation environment is complex.