Common faults inside voltage transformers - Solutions - Huaqiang

(l) For voltage transformers, more occurs because the design structure is unreasonable, causing the core core-through bolt to suspend and discharge during operation. This type of failure was more common in the 1980s. At present, with the improvement of the domestic design structure, the newly put into operation voltage transformer has been greatly improved in this respect. Another common fault of the voltage transformer is the poor insulation bracket, followed by poor end seals and moisture ingress. Table 6 shows the statistics of the faults of 25 voltage transformers detected by gas analysis in oil. Table 6-10 Statistics on fault causes of 25 voltage transformers

Fault nature failure cause number of floating potential discharge core bolt and iron core connection loose, causing the bolt to be in suspension potential 7 metal foreign matter is in suspension potential discharge 1 insulation bracket nut potential suspension 1 arc discharge cascade winding on iron core discharge, poor insulation support The discharge 7 is insulated and the water is damp. 2 The end of the primary winding is not grounded. 1 Other unexplained reasons (exit operation is not checked) 3 The cause of the overheating fault is unknown, but 1and is large and the insulation performance is degraded (no internal inspection, shutdown) 3 (2) Common faults in current transformers are often associated with manufacturing defects. Here is only briefly described 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. malfunction. 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) Since the green 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. Table 6-11 shows the statistics of the faults of 45 current transformers and is for reference only. Table 6-11 Statistics on the causes of faults in 45 current transformers Fault nature failure cause number of floating potential discharge primary winding support nut loose, causing primary winding shield aluminum platinum potential suspension 4 secondary winding to ground breakdown secondary open circuit insulation moisture 1 2 shielding layer breakdown main screen has a disconnect, less End screen, resulting in uneven potential distribution 2 Partial discharge between the main screen, the paper near the end screen and the surface of the aluminum platinum has a large amount of X wax, tana increases the apparent 3 U-shaped capacitor core bottom to the ground discharge diaphragm rupture, seal damage, water Damp 3 Last screen capacitive screen breakdown or poor grounding to the ground discharge, the last screen is unsoldered, the insulation is damp. 4 Other discharge faults are unknown (exit operation, no internal inspection) 12 Local overheating Once the lead fastening nut is loose , the tapping nut is loose, and the end screen grounding nut is loose 14