Common faults in current transformers are often related to manufacturing defects, as follows:
1) The insulation of the current transformer is very thick, some insulation is loosely wrapped, wrinkles are formed between the insulation layers, and the vacuum treatment is poor, and the impregnation is incomplete, resulting in a gas-containing cavity, which is easy to cause partial discharge failure.
2) The size and arrangement of the capacitor screen do not meet the design requirements, even the capacitive screen is less placed, the capacitor plate is not smooth and even, or even misplaced or broken, so that the voltage equalization characteristic is destroyed. Therefore, when the electric field strength along the surface of the local solid insulation reaches a certain value, partial discharge is caused.
The direct consequence of the partial discharge described above is that the insulating oil is cracked, and a large amount of x wax is generated between the insulating layers, and the dielectric loss is increased. This type of discharge has a cumulative effect, and as it develops, gas analysis in oil will be characterized by arcing.
3) Because the insulating material is not clean or contains high humidity, it may cause creeping discharge on its surface. This situation is more common in the discharge of the terminal leads along the surface of the pad.
4) Some loose connections or suspension of metal parts will cause spark discharge. For example, the loosening of the primary winding support nut will cause the primary winding shield aluminum foil to be suspended, and the last screen lead contact or poor soldering or even wire breakage will cause such a fault.
5) - The secondary connection clamp, bolts and nuts are loose, the grounding nut of the final screen is loose, and the tapping nut is loose, which can increase the contact resistance, resulting in local overheating failure. In addition, improper on-site maintenance management should also be taken seriously. For example, the transformer's water ingress is damp, although it may be related to the sealing structure and sealing material of the manufacturer, but there are also problems with maintenance management. In general, on-site vacuum degassing is insufficient or vacuum drying is not performed during maintenance, so that the dissolved gas in the oil is easily saturated or the residual bubbles and moisture in the oil-paper insulation are high. All of this will leave a safety hazard to the device.