Common failures of current transformers are often related to manufacturing shortcomings, as detailed below:
1. The insulation of the CT current transformer is very thick, some insulation wraps are loose, and there are wrinkles between the insulation layers. In addition, the vacuum treatment is poor, and the impregnation is incomplete to form an air-containing cavity, which is easy to cause partial discharge failure.
2. The size and arrangement of the capacitive screen of the CT current transformer do not meet the design requirements, so as to discharge the capacitive screen at least, the capacitive plate is not lubricated and flat, and even dislocated or broken, which destroys the voltage equalization characteristics. Therefore, when the electric field strength along the surface of some solid insulation reaches a certain value, a partial discharge will be formed.
The direct result of the above-mentioned partial discharge is to crack the insulating oil, generate a large amount of x-wax between the insulating layers, and increase the dielectric loss. This discharge has a cumulative effect, and if it continues, the gas-in-oil analysis will likely exhibit the characteristics of arcing.
3. Because the insulating material of the CT current transformer is not clean or contains high humidity, creeping discharge may occur on its surface. This situation is more common when the terminal leads are discharged along the surface of the pad.
4. The loose connection of some current transformers or the potential suspension of metal parts will lead to spark discharge. For example, the primary winding support nut is loose, forming the potential suspension of the primary winding shielding aluminum foil, and the contact of the terminal lead or poor welding leads to disconnection. Fault.
5. The looseness of the splint, bolts and nuts of the primary connection of the CT current transformer, the looseness of the grounding nut of the last screen, the looseness of the tap tightening nut, etc., may increase the contact resistance and cause some overheating failures.
In addition, improper on-site maintenance management should also be paid attention to. For example, if the CT current transformer is wetted by water, it may be related to the sealing structure and sealing material of the manufacturer, but there are also maintenance management problems.
Generally speaking, the on-site vacuum degassing is insufficient or the vacuum drying is not carried out during maintenance, resulting in easy saturation of the dissolved gas in the oil or residual air bubbles and high moisture content in the oil-paper insulation. All of these will leave a security risk to the device.
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