What are the common causes of grounding faults on the secondary side of current transformers?

1. Grounding wire problems
Wire breakage or damage: Long-term mechanical external forces, such as frequent vibration and pulling, may cause the grounding wire to break. For example, in a current transformer installed near a large motor or equipment, the vibration transmission of the motor may cause the connection part of the grounding wire to gradually loosen until it breaks. In addition, environmental factors can also cause wire damage. For example, in an outdoor environment, the grounding wire may be exposed to wind, rain, sun and ice, causing the insulation sheath to age and crack, thereby exposing and damaging the internal metal wire.
Poor connection: Improper connection between the grounding wire and the grounding terminal or loose connection is a common problem. For example, during the installation process, if the appropriate connection tool is not used or the connection nut is not tightened, the contact resistance will increase. Over time, the connection may further deteriorate due to oxidation, corrosion and other reasons, eventually leading to poor grounding.
2. Grounding terminal failure
Corrosion and oxidation: If the current transformer is installed in a harsh environment such as humid, corrosive gas (such as a chemical site) or coastal areas, the grounding terminal is susceptible to corrosion and oxidation. The corrosion products will form an insulating layer on the surface of the terminal, increase the grounding resistance, and affect the grounding effect. For example, in a substation near the sea, the salt content in the air is high, and the grounding terminal is easily corroded.
Mechanical damage: The grounding terminal may be damaged by mechanical external forces such as accidental collision and extrusion. For example, during equipment installation, maintenance or other construction processes, the grounding terminal may be accidentally touched, causing it to deform, loosen or be damaged, thereby affecting the reliability of grounding.
3. Insulation damage
Secondary winding insulation aging: The insulation material of the secondary winding of the current transformer will gradually age during long-term operation. This may be caused by factors such as long-term temperature changes, electric field effects, or chemical corrosion. Insulation aging will lead to a decrease in insulation performance, a decrease in the insulation resistance between the secondary winding and the ground, and even insulation breakdown, which may cause a grounding fault. For example, the aging rate of the insulation material of a current transformer operating in a high temperature environment will accelerate.
Insulation dampness: If the sealing performance of the current transformer is not good, moisture may enter the interior and cause the secondary winding to damp. For example, in a basement or indoor environment with high humidity, when the sealing gasket of the transformer is aged or damaged, external water vapor can easily enter, causing the winding insulation to be damp, reducing the insulation resistance and causing a ground fault.
4. External interference and abnormal current path
Electromagnetic interference: In the power system, the strong electromagnetic field generated by the surrounding large electrical equipment (such as transformers, high-power motors, etc.) may interfere with the secondary grounding system of the current transformer. These interferences may induce electromotive force in the grounding loop, causing abnormal grounding current and affecting the normal function of grounding. For example, when a short circuit fault occurs in a nearby transformer, the strong magnetic field generated may interfere with the grounding of the secondary side of the current transformer.
Unexpected conductive path: In some complex electrical systems, unexpected conductive paths may occur. For example, because the metal casing of the equipment is not well grounded or is in contact with other live parts, an abnormal current path through the secondary grounding system of the current transformer may be formed, causing a ground fault.