What are the methods for dealing with grounding faults on the secondary side of current transformers?

1. Dealing with grounding wire faults
Repair of wire breakage
Reconnection: If the grounding wire is broken, first cut off the power supply on the primary side of the current transformer (if possible) to ensure safety. Then clean the oxide layer and impurities at the break, and use appropriate connection tools (such as crimping pliers or welding equipment) to reconnect the broken wire. For example, for grounding wires with smaller cross-sectional areas, crimping can be used to connect the two sections of wires firmly using professional crimping terminals to ensure good conductivity of the connected part.
Replacing the wire: If the grounding wire is severely damaged and cannot be effectively repaired, a new grounding wire needs to be replaced. When replacing, choose according to the specifications and length of the original wire to ensure that the new wire can meet the grounding requirements. When installing a new wire, pay attention to the correct wiring method to avoid mechanical damage to the wire, and at the same time ensure that the connection between the wire and the grounding terminal is firm and reliable.
Poor connection handling
Cleaning and tightening the connection point: When it is found that the grounding wire is poorly connected to the grounding terminal, first disassemble the connection point and clean the oxide layer, dirt and corrosion products at the connection site. You can use tools such as sandpaper and wire brushes to clean it, and then re-tighten the connection nut to ensure a tight connection. When tightening the connection point, pay attention to using the appropriate torque to avoid over-tightening or over-loosening.
Replacement of connection accessories: If the connection accessories (such as nuts, washers, etc.) are damaged or severely corroded, new accessories should be replaced. When selecting new accessories, make sure that their materials and specifications are the same as the original accessories and have good conductivity and corrosion resistance. For example, for grounding systems used in corrosive environments, stainless steel connection accessories can be selected.
2. Grounding terminal fault handling
Corrosion and oxidation treatment
Surface treatment: When the grounding terminal is corroded or oxidized, the terminal surface must be treated first. The corrosion and oxidation layer can be removed with tools such as sandpaper and files to reveal the metallic luster. During the treatment process, be careful not to damage the terminal body structure. Then, the cleaned terminal surface is treated with anti-rust, such as applying conductive paste, anti-rust paint, etc., to prevent corrosion again.
Replacement of terminals: If the grounding terminal is severely corroded and has affected its mechanical strength or conductivity, you should consider replacing it with a new grounding terminal. When replacing, ensure that the installation position and connection method of the new terminal are the same as the original terminal, and ensure that the new terminal is well connected to the grounding wire and the equipment housing.
Mechanical damage repair
Reshaping and reinforcement: For grounding terminals damaged by mechanical external forces, such as slight deformation, you can try to reshape and repair. Use tools such as pliers and wrenches to restore the terminal to its original shape, and then check its connection performance. If the fixed part of the terminal is loose, you can add gaskets or replace the fastening bolts to reinforce it to ensure the stability of the terminal.
Replacement of damaged parts: If the key parts of the grounding terminal (such as connection holes, terminals, etc.) are damaged and cannot be repaired, the entire grounding terminal needs to be replaced. After replacement, a comprehensive inspection, including grounding resistance test, connection reliability check, etc., should be carried out to ensure the normal operation of the grounding system.
3. Insulation damage treatment
Insulation aging treatment
Replacement of insulation material: If the insulation material of the secondary winding of the current transformer ages, resulting in a decrease in insulation performance, the insulation material generally needs to be replaced. This is a relatively complicated process that requires professional maintenance personnel to operate. First, disassemble the current transformer, carefully remove the aged insulation material, and then replace the new insulation material, such as epoxy insulation board, polyimide film, etc., according to the specifications and models of the original insulation material. During the replacement process, pay attention to the installation process of the insulation material to ensure that it fits the winding tightly to avoid bubbles or gaps.
Drying treatment: In some cases, insulation aging may be accompanied by damp winding. The current transformer can be dried to remove moisture and restore insulation performance. Common drying methods include oven drying and hot air drying. Put the current transformer in the oven and set the appropriate temperature (generally 80-100℃) and time (depending on the degree of moisture, it may take several hours to several days) for drying. During the drying process, pay attention to temperature control to avoid excessive temperature from damaging other parts of the transformer.
Insulation damp repair
Dehumidification and sealing repair: If the secondary winding of the current transformer is found to be damp, dehumidification measures must be taken first. The transformer can be placed in a dry and ventilated environment, or dehumidified using dehumidification equipment (such as a dehumidifier). At the same time, check the sealing performance of the transformer, repair or replace the damaged sealing gasket to prevent moisture from entering again. For example, for transformers with poor sealing, you can apply sealant to the sealing gasket to enhance the sealing effect.
Insulation resistance test after recovery: After dehumidification and sealing repair, use an insulation resistance meter to test the insulation resistance between the secondary winding and the ground. Only when the insulation resistance returns to the normal range can the transformer be put back into use. And for a period of time after being put into use, it is necessary to strengthen the monitoring of insulation resistance to ensure stable insulation performance.
4. External interference and abnormal current path processing
Elimination of electromagnetic interference
Strengthening shielding measures: If the secondary side grounding system of the current transformer is subject to electromagnetic interference, the existing shielding measures must be checked and strengthened first. For the grounding wire, a metal shielding layer can be added and the shielding layer must be well grounded. For example, a copper shielding net is used to wrap the grounding wire, and both ends of the shielding net must be reliably connected to the grounding terminal to form a complete shielding loop to guide the induced current generated by external electromagnetic interference to the ground.
Adjust equipment layout (if feasible): If conditions permit, consider adjusting the relative position of the current transformer and the interference source (such as large motors, transformers, etc.). Increase the distance between the two, or change the installation direction of the equipment to reduce the impact of electromagnetic interference. For example, in the layout planning of the substation, the current transformer can be moved to a position farther away from the transformer, or an electromagnetic shielding wall can be set between the two.
Abnormal current path investigation and cut-off
Comprehensive inspection of the conductive path: When an abnormal current path is found, the entire electrical system should be thoroughly inspected. Check whether the metal casing, pipelines, cable trays and other components that may form a conductive path of the equipment have unexpected connections with the grounding system. Use tools such as insulation resistance meters to check the insulation between these components and the grounding system one by one.
Cut off abnormal connections: Once an abnormal conductive path is found, take measures to cut off the connection. For example, if it is found that the metal casing of the equipment is short-circuited with the grounding system, check the connection method of the casing grounding, repair the damaged insulation part, or adjust the connection position to ensure that the casing is grounded normally to avoid abnormal current passing through the grounding system.