Abstract: In substation design, this paper analyzes the design scheme of 110kV outdoor sulfur hexafluoride electrical equipment foundation in special areas, and proposes precautions for the design of this type of foundation for reference by colleagues. Keywords: Electrical equipment foundation design 1 Introduction The 110kV outdoor high-voltage sulfur hexafluoride circuit breaker is a very important control and protection device in the substation. Due to its relatively thin and tall structure, the foundation is prone to deformation during use, which affects its operation. Therefore, before designing, it is necessary to conduct a detailed analysis of the geological conditions of the substation site, obtain accurate geological data, and adopt a reasonable structural design to ensure the stability of the foundation, thereby achieving the goal of safe operation. 2. Electrical Equipment Foundation Design The foundation design for substation electrical equipment should ensure strong stability and resistance to deformation. Technical requirements for 110kV outdoor sulfur hexafluoride (LW21-110 type) circuit breakers: 1) The circuit breaker's static total load is 20kN, upward moving load is 50kN, and downward moving load is 80kN; 2) The circuit breaker's base is fixed with 8 M24 anchor bolts, which should be vertically anchored; 3) Shims should be used to ensure the circuit breaker's three-stage mounting flange surface remains horizontal. For example, the geological conditions of a 110kV substation project in a certain region of Xinjiang are as follows: soil, with a 0.8m layer of silty sand on the surface and a lower layer of fine sand; the design considers it as sandy clay; groundwater level: highest at 0.8m in spring (March-April), generally below 1.2m; maximum frost depth: 0.71m; foundation bearing capacity: 8t/m². The circuit breaker foundation design scheme (see Figure 1 for the overall shape of the circuit breaker, and Figure 2 for the embedded bolts and foundation plan) is determined as follows: 1) Eight anchor bolts are fixed to the foundation. The horizontal spacing from left to right is 1.45m, 0.5m, and 1.45m, and the longitudinal spacing is 0.524m in the middle and 0.32m on the left and right sides. 2) Based on the location of the anchor bolt holes, a column-shaped pier integral base plate structure is adopted. One central pier and two side piers are designed. The central pier is 1.1m wide, 1.1m long, and 1.3m high. The side piers are 0.5m wide, 0.82m long, and 1.3m high. The foundation is exposed. 1) The pre-embedded hole is 0.3m above ground level and 1.0m underground. The distance from the edge of the pre-embedded hole to the edge of the pier is controlled to be no less than 0.15m; 2) A reinforced concrete monolithic slab is set at the bottom of the pier to enhance the integrity, stability and deformation resistance of the foundation structure. The slab thickness is controlled to be greater than 0.20m, and the bottom of the foundation is set at least 0.2m below the maximum frost depth; 3) The concrete grade of the equipment foundation is no less than C15, and the secondary grouting concrete is C20; 4) An integral base slab is added under the pier. The structure is conducive to resisting foundation deformation and ensuring the stability of equipment foundations; 6) The bottom slab structure uses concrete with a grade not lower than C15, a bottom thickness of 0.25m, and the bottom reinforcing bars should not be less than Φ8. The spacing should not be greater than 20cm, and the distribution bars can be Φ6@200 or Φ8@250. 7) Foundation self-weight: middle pier W1=30.5kN, side pier W2=22.7kN, bottom slab W3=31.7kN, equipment self-weight W4=20kN, total weight W=104.9kN. Calculations show that the self-weight of the support is 73.2 kN, which is greater than the upward load of the circuit breaker equipment (50 kN). The safety factor is 1.46. Therefore, adding a base slab under the support is a structural measure to enhance stability. The required foundation slab area is calculated as S = 3.54 m², while the actual foundation slab area is calculated as S ' = 5.25 m² > 3.54 m². The safety factor K = 1.49, which meets the requirements. Points to note in equipment foundation design: 1) Under the premise of meeting the requirements of foundation stability and deformation, the foundation should be buried as shallow as possible. When the bearing capacity of the upper foundation layer is greater than that of the lower layer, the upper layer should be used as the bearing layer; 2) The foundation should preferably be buried above the groundwater level. When it must be buried below the groundwater level, measures should be taken to ensure that the foundation soil is not disturbed during construction; 3) When using a weak soil layer as the bearing upper layer, it is advisable to cover it with a better soil layer. When the overlying soil layer is thin, care should be taken to avoid disturbing the loose soil during construction. 4) When the groundwater level is high (depth less than 2.3m) and the foundation is in a moderately moist condition, anti-corrosion measures should be taken for the foundation. Two coats of hot-applied asphalt should be applied to the contact surface with the soil. In areas where the soil has moderate to severe corrosion damage to concrete, the foundation concrete standard should be increased to C25, and the water-cement ratio should be controlled to less than 0.5, followed by two coats of hot-applied asphalt for anti-corrosion. 5) When the groundwater level is too high (depth less than 1.5m), the soil moisture content is high, and the foundation bearing capacity is low, backfilling with gravel can be used to artificially strengthen the foundation. In areas with suitable conditions, wrapping the gravel with special geotextile fabric will further enhance the foundation's effectiveness. Artificial gravel foundations can be designed according to the requirements of rigid foundations. 6) When the equipment foundation is located in frost-susceptible soil, the impact of frost heave on foundation deformation is significant. The bottom of the foundation should be set 0.2m below the maximum average frost depth over many years . In areas with high groundwater levels, if the concrete structure is susceptible to frost heave damage, the design should also refer to the methods for concrete resistance to salt and alkali corrosion for reinforcement. Conclusion The foundation of electrical equipment in a substation is one of the most important guarantees for the normal operation of the equipment. The stability of the foundation is crucial. Before designing, a detailed analysis of the site's geological conditions is essential to obtain accurate geological data and select a suitable site. If the site has poor geological conditions, reliable measures must be taken in the design. For sandy soil foundations, shallow burial is necessary, along with increasing the foundation size and the size of the artificial bedding layer. In cold regions with high water levels, the frost resistance of the foundation should also be considered. In short, the design of electrical equipment foundations must include calculations of bearing capacity, deformation, and stability, and a reasonable, economical, and safe foundation should be developed based on the actual geological conditions.