I. Winding Faults
Winding faults are one of the most serious types of faults in transformers, mainly including inter-turn short circuits, inter-phase short circuits, winding grounding, and disconnections. According to statistics, winding faults account for more than 40% of the total transformer failure rate.
1. Causes of Faults
Insulation Defects: During the manufacturing process, there are local damages or impurity residues in the winding insulation materials. After long-term operation, short circuits are likely to occur.
Overload and Poor Heat Dissipation: Long-term overloading operation causes the temperature of the winding to rise too high, accelerating the aging of the insulation and even leading to carbonization breakdown.
Mechanical Stress Impact: The electromagnetic force generated by external short-circuit currents or lightning strikes can cause the winding to deform and displace, thereby damaging the insulation structure.
2. Fault Manifestations
Abnormal Oil Chromatography: The local high temperature at the short-circuit point decomposes the insulating oil, generating a large amount of combustible gases such as hydrogen and methane.
Abnormal Operating Parameters: The DC resistance is unbalanced, the no-load current increases, and there are abnormal noises such as a "boiling sound" inside the oil tank.
Protection Device Operation: Differential protection and gas protection (light gas alarm or heavy gas tripping) may be triggered.
3. Treatment Measures
Immediately shut down and disconnect the power supply to prevent the fault from expanding.
Use a winding deformation tester to detect the degree of deformation and determine whether the winding needs to be replaced.
Repair the insulation at the local short-circuit point. In severe cases, the entire winding needs to be replaced, and the heat dissipation design should be strengthened.
II. Insulation Faults
The insulation system is the cornerstone of the safe operation of transformers. Its faults mostly manifest as problems such as deterioration of oil quality, aging of solid insulation, and moisture ingress, accounting for 30% to 35% of the total number of faults.
1. Types and Causes of Faults
Oil Insulation Failure: The intrusion of moisture or oxidation leads to an increase in the dielectric loss of the oil and a decrease in the breakdown voltage. This is common in transformers with poor sealing or failed breathers.
Solid Insulation Aging: Long-term operation at high temperatures makes the paper insulation fibers brittle, reducing the dielectric strength and ultimately causing partial discharge or breakdown.
Composite Insulation Moisture Ingress: The failure of the bushing seal or the blockage of the oil conservator breather leads to the intrusion of moisture between the layers of the insulating paperboard.
2. Diagnostic Methods
Oil Test Analysis: Detect the water content, acid value, and furfural content to evaluate the degree of aging.
Partial Discharge Detection: Use ultrasonic or ultra-high frequency sensors to locate the discharge point and determine the location of the insulation defect.
Frequency Domain Dielectric Spectroscopy (FDS): Analyze the polarization characteristics of the insulation material to quantify the humidity and aging state.
3. Countermeasures
Replace or regenerate the deteriorated insulating oil, and strictly control the oil injection process and vacuum degree.
Conduct hot oil circulation drying on the damp insulation to restore its dielectric performance.
Install an online monitoring system to track the oil temperature, humidity, and partial discharge quantity in real-time.
III. Discharge Faults
According to the energy density, discharge faults can be divided into partial discharge, spark discharge, and high-energy arc discharge, mostly caused by insulation defects or structural abnormalities, accounting for 20% to 25% of the fault cases.
1. Fault Mechanisms
Partial Discharge: The ionization of air bubbles in the oil or cavities inside the solid insulation under the electric field generates low-energy repetitive discharges. Long-term accumulation leads to insulation degradation.
Spark Discharge: Intermittent discharges occur between the floating potential components (such as loose iron core clamping parts) and the grounding body, which is common in transformers with more impurities in the oil.
Arc Discharge: The insulation between winding turns or the lead wire to the ground breaks down, releasing high-energy arcs, which may cause explosions and fires.
2. Characteristics and Hazards
Gas Generation: Characteristic gases such as hydrogen (H₂) and acetylene (C₂H₂) are generated during the discharge process and can be identified through chromatographic analysis.
Abnormal Temperature Rise: The local temperature at the discharge point rises sharply, accelerating the decomposition of the oil and triggering a chain reaction.
Equipment Damage: High-energy discharges can burn out the winding, melt through the iron core, and even cause the oil tank to burst.
3. Prevention and Control Measures
Structural Optimization: Eliminate sharp corners and burrs, ensure single-point grounding of the iron core, and avoid floating potentials.
Oil Quality Management: Regularly filter and purify the oil to remove metal particles and fiber impurities and maintain the oil's dielectric strength.
Intelligent Monitoring: Deploy ultraviolet imaging devices and ultra-high frequency sensors to achieve early warning of discharges.
Conclusion
The winding, insulation, and discharge faults of power transformers are the main risk sources threatening the safety of the power grid. Through accurate diagnostic technologies (such as oil chromatography analysis and partial discharge monitoring) and preventive maintenance (such as insulation enhancement and structural optimization), the failure rate can be significantly reduced. In the future, with the popularization of intelligent sensing and AI prediction technologies, transformer fault management will develop towards automation and precision, further improving the reliability of the power system.
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