1) The insulation of the current transformer is very thick, and some insulation is loosely wrapped, and there are wrinkles between the insulation layers. In addition, poor vacuum treatment and incomplete impregnation result in air-containing cavities, which may easily cause partial discharge failure.
2) The size and arrangement of the capacitive screen do not meet the design requirements, or even less discharge of the capacitive screen, the capacitive plate is not smooth and flat, or even dislocated or broken, which destroys the pressure equalization characteristics. Therefore, when the electric field strength along the surface of the local solid insulation reaches a certain value, it will cause partial discharge.
3) Because the insulating material is not clean or has high moisture content, creeping discharge may occur on its surface. This situation is more common when a terminal lead discharges along the surface of the pad.
4) Some loose connections or potential suspension of metal parts will cause spark discharge, such as the loosening of the primary winding support nut, causing the potential of the primary winding shielding aluminum foil to float, poor contact or welding of the final screen lead, or even disconnection, which will cause such failures.
5) The secondary connection splint, bolts and nuts are loose, the grounding nut of the end screen is loose, and the tap tightening nut is loose, etc., which may increase the contact resistance and cause local overheating failure. In addition, improper on-site maintenance and management should also cause attention. For example, the water-inflow of the transformer may be related to the sealing structure and sealing material of the manufacturer, but there are also maintenance and management issues. Generally speaking, the on-site vacuum degassing is insufficient or vacuum drying is not carried out during maintenance, which causes the dissolved gas in the oil to be easily saturated or the residual air bubbles and high moisture content in the oil-paper insulation. All of these will leave safety hazards to the equipment.https://www.ctsensorducer.com/