When installing transformer clamps, attention should be paid to multiple details to ensure installation quality. Firstly, before installation, check the size, flatness, and surface treatment of the clamps to ensure they meet the design requirements. Secondly, when clamping the iron core, ensure uniform force to avoid iron core deformation due to local over-tightening or over-loosening, which can be achieved by adjusting the tightness of the tension screws. In addition, the connection between the clamps and other accessories should be firm. The quality of the welded parts should be checked, and the bolt connections should be tightened in place to prevent loosening during operation, which may affect the normal operation of the transformer.
Conformity of Transformer Clamps with Industry Standards
The production and manufacturing of transformer clamps are subject to strict industry standards throughout the process, and each link has clear specification requirements. In terms of dimensional accuracy, the national standard GB/T 10228-2015 "Technical Parameters and Requirements for Dry-type Power Transformers" stipulates that the frame perpendicularity deviation of the clamp shall not exceed 1mm/m, the positional tolerance of bolt holes is ±0.5mm, and the hole distance tolerance is ±0.3mm. These requirements ensure that the assembly gap between the clamp and the iron core and windings is controlled within 0.5mm, avoiding additional vibration caused by excessive gaps during operation. For transformers with oriented silicon steel sheet cores, the parallelism tolerance of the upper and lower yoke clamps of the clamp is higher, which needs to be controlled within 0.3mm/m to ensure the uniformity of the magnetic circuit of the iron core.
In terms of material selection, clamp materials of different grades need to pass strict certification: the clamp steel used for transformers of 110kV and above must meet the requirements of GB/T 3077-2015 "Alloy Structural Steels". Its chemical composition (such as carbon content ≤0.20%, sulfur and phosphorus content ≤0.035%) and mechanical properties (tensile strength, impact energy, etc.) must be inspected and qualified by a third-party testing agency, and a material certificate must be issued. For low-magnetic steel clamps, the industry standard JB/T 10319-2002 "Low-magnetic Steel Sheets for Transformers" stipulates that their iron loss at 50Hz and 1.5T magnetic field shall be ≤0.3W/kg to ensure that no additional loss is added to the transformer.
Performance testing is a key link to verify whether the clamp meets the standards. In the short-circuit impact test, the clamp must withstand the electromagnetic force generated by a short-circuit current equivalent to 25 times the rated current for 2 seconds. After the test, the deformation of the clamp is checked, requiring the maximum deflection to not exceed 1/500 of the span, and no cracks in the welded parts. The corrosion resistance test adopts the neutral salt spray test (GB/T 10125-2021). After 500 hours of continuous spraying, the rust grade of the clamp surface must reach Ra5 or above in GB/T 6461-2002, that is, the rust area does not exceed 5%. In addition, for clamps used in hot and humid areas, a damp heat test is also required. After being placed in an environment with a temperature of 40℃ and a relative humidity of 90% for 1000 hours, the adhesion of its insulating coating (cross-cut method) must reach level 1 to ensure good performance in humid environments.
The continuous update of industry standards is also promoting the progress of clamp technology. For example, the latest GB/T 1094.1-2023 "Power Transformers - Part 1: General" adds requirements for the environmental protection performance of clamps, stipulating that the volatile organic compound (VOC) content of their surface coatings shall not exceed 300g/L, which promotes the application of low-pollution coatings in clamp manufacturing, making transformer clamps more in line with the development trend of green environmental protection while meeting safety performance.
