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Common faults of current transformers are as follows:
1) The insulation of the current transformer is very thick, and some insulation wraps loosely, and there are wrinkles between the insulation layers. In addition, the vacuum treatment is poor, and the impregnation is incomplete, resulting in air-containing cavities, which easily cause partial discharge failures.
2) The size and arrangement of the capacitive screen do not meet the design requirements, and even the capacitive screen is under-discharged. The capacitive plates are not smooth and flat, or even misplaced or broken, which destroys the voltage equalization characteristics. Therefore, when the electric field intensity along the surface of the local solid insulation reaches a certain value, partial discharge will be caused. The direct consequence of the above partial discharge is to crack the insulating oil, generate a large amount of wax between the insulating layers, and increase the dielectric loss. This kind of discharge has a cumulative effect. If it continues to develop, the gas analysis in oil may show the characteristics of arc discharge.
3) Since the insulating material is not clean or has high moisture content, surface discharge may occur on its surface. This situation is more common when the primary terminal lead discharges along the surface of the pad.
4) Some loose connections or potential suspension of metal parts will cause spark discharge. For example, the support nut of the primary winding is loose, causing the potential suspension of the shielding aluminum foil of the primary winding.
5) Loose splints, bolts, and nuts for the secondary connection, loose grounding nuts for the last screen, loose tap fastening nuts, etc., may increase the contact resistance and cause local overheating faults. In addition, improper on-site maintenance management should also be taken seriously. For example, if the transformer gets wet from water, although it may be related to the sealing structure and sealing material of the manufacturing plant, there are also maintenance and management issues. Generally speaking, the on-site vacuum degassing is insufficient or the vacuum drying is not carried out during maintenance, resulting in the dissolved gas in the oil being easily saturated or the residual air bubbles and high moisture content in the oil-paper insulation. All of these will leave potential safety hazards to the equipment.