Insulation Sleeve Application Notes

Installation errors must be strictly controlled. During construction, if the inclination of the bushing axis exceeds 0.5°, it may cause electric field distortion. There was a wind farm that caused the actual value of the 35kV bushing external insulation distance to be 8% less than the designed value due to installation deviation, and insulation failure occurred after three months of operation.
Daily inspections should focus on key points. Infrared temperature measurement and ultraviolet imaging are combined to focus on whether the temperature rise on the bushing surface is abnormal and whether there are traces of corona discharge. A power supply company found weak discharge at the bushing flange through ultraviolet detection, and timely treatment avoided flashover accidents caused by carbonization on the surface of the insulator.
Special situations should be adjusted in time. When new buildings or vegetation growth around the equipment may change the air gap, the insulation distance needs to be re-calibrated. Due to the construction of a new billboard outside the wall of a certain city substation, the distance between Switchgear Insulating Bushing pairs of obstacles was reduced from the designed 3.2 meters to 2.8 meters. The problem of insufficient distance was compensated by adding anti-pollution flashover paint and RTV coating.
Maintenance strategies need to be differentiated. In foggy areas, the bushing surface should be cleaned every quarter, and industrial pollution areas are recommended to conduct pollution detection every month. A chemical plant's self-provided substation installed an online leakage current monitoring device to achieve real-time early warning of the contamination status of the bushing surface, shortening the preventive cleaning cycle from three months to two weeks.
In technical transformation projects, there have been cases of design errors due to ignoring historical data. When renovating an old substation, the designer directly applied the new standard to calculate the insulation distance of the 35kV bushing as 420mm, but the actual on-site measurement of the original structure spacing was only 380mm. In the end, the creepage distance was increased by adding silicone rubber umbrella skirts, avoiding the delay in the construction period caused by civil engineering transformation.
It should be noted that there is a restrictive relationship between the mechanical strength of the bushing and the insulation distance. Excessive pursuit of a large insulation distance may cause the bushing to be too long and structural damage under wind or seismic loads. A 750kV substation had a bushing that broke in strong winds due to a large aspect ratio. The problem was solved by improving the support structure and optimizing the insulator layout.
For bushings installed in special places such as tunnels, in addition to considering conventional parameters, it is also necessary to evaluate the impact of ventilation conditions on the insulation distance. In the subway power supply system, due to the poor air flow in the tunnel, the surface of the bushing is in a high humidity environment for a long time. The insulation distance is increased by 25% compared with the conventional value during the design, and an active dehumidification device is installed to ensure safe operation.
In the equipment selection stage, it is recommended to establish a multi-dimensional evaluation system. The insulation distance index is considered comprehensively with factors such as cost, maintenance convenience, and supplier technical strength. When purchasing 110kV bushings, a provincial power grid company adopted a bidding evaluation method with a technical score of 60% and a business score of 40%, eliminating the products with the lowest bid but insufficient insulation margin, and controlling quality risks from the source.
Professional judgment is required when encountering standard conflicts. When there are differences between national standards and IEC standards, domestic standards should be implemented first, but technical reports of international standards can be referred to. A foreign-funded enterprise EPC project once directly adopted the IEC 60137 standard to design the bushing insulation distance, without considering the characteristics of the actual domestic operating environment, resulting in frequent flashover after the equipment was put into operation, and the later rectification cost was as high as 40% of the original investment.
Finally, it is emphasized that any theoretical calculation needs to be verified on site. Before new equipment is put into operation, it is necessary to use laser rangefinders, 3D scanners and other tools to verify key dimensions. It was found that the actual insulation distance of a batch of bushings was 5% smaller than the design value due to manufacturing errors. Through full inspection and screening, batch quality accidents were avoided.
Only by systematically grasping the balance between design specifications, environmental variables and engineering experience can we ensure that the insulation distance outside the bushing meets safety requirements while avoiding waste of resources caused by over-design. The precise control of this parameter is essentially a process of finding the optimal solution between electrical performance, mechanical strength and economic benefits.