What are the common faults of oil-immersed transformers, and what are the best solutions?

1. Overview of Oil-immersed Transformers and Significance of Fault Research

As a key equipment in power systems, oil-immersed transformers undertake the important tasks of voltage transformation and electric energy transmission. Their stable operation is directly related to the safe and reliable power supply of power systems. However, during long-term operation, transformers will inevitably face various fault challenges, which affect their performance and even lead to system paralysis. According to statistics, transformer faults account for approximately 15%-20% of all equipment faults in power systems, and oil-immersed transformers have more complex fault types due to their structural characteristics and operating environment.

The early identification and effective handling of oil-immersed transformer faults are crucial for ensuring grid safety. In-depth research on transformer fault types, causes and solutions can not only improve the reliability and service life of transformers, but also provide scientific fault diagnosis and handling guidance for operation and maintenance personnel, reducing power outage time and maintenance costs. With the advancement of smart grid construction, higher requirements are put forward for the fault diagnosis and handling technology of oil-immersed transformers, and systematic research and summary are urgently needed.

1.1 Basic Structure and Working Principle of Oil-immersed Transformers

An oil-immersed transformer is mainly composed of an iron core, windings, oil tank, insulating oil, cooling system, protection device and other components. Its basic working principle is based on the law of electromagnetic induction, realizing the transmission of electric energy and voltage transformation through electromagnetic coupling between windings.

• Iron Core: As the magnetic circuit part of the transformer, it is usually made of laminated silicon steel sheets with insulating paint coated on the surface to reduce eddy current loss. The iron core forms a closed magnetic circuit, enabling the effective transmission of magnetic flux generated in the windings.
• Windings: As the circuit part of the transformer, they are usually made of copper or aluminum wires, divided into high-voltage windings and low-voltage windings. The windings are isolated from each other by insulating materials and kept insulated from the iron core.
• Insulating Oil: As the insulation and cooling medium of the transformer, it has good electrical insulation performance and heat conduction performance, which can absorb and transfer heat during operation and participate in insulation protection at the same time.
• Cooling System: It includes radiators, fans, oil pumps and other components, responsible for dissipating the heat generated during transformer operation to the surrounding environment, ensuring that the temperature of each part of the transformer is within the allowable range.
• Protection Device: It includes gas relays, pressure relief valves, thermometers, etc., used to monitor the operating status of the transformer and issue alarm signals or trip protection in case of abnormalities.

2. Analysis of Main Fault Types and Characteristics of Oil-immersed Transformers

Oil-immersed transformers have various fault types. According to the nature and location of faults, they can be divided into five categories: winding faults, iron core faults, insulation faults, oil quality faults and accessory faults. Each type of fault has its unique characteristics and cause mechanisms.

2.1 Analysis of Winding Faults

Winding faults are one of the most common fault types of oil-immersed transformers, accounting for about 30%-40% of total transformer faults. Winding faults mainly include turn-to-turn short circuits, winding grounding, wire breakage and other forms, which seriously affect the normal operation of the transformer.

• Turn-to-turn Short Circuit: It is the most common type of winding fault, manifested as a short circuit between adjacent turns of the same phase in the winding. A slight turn-to-turn short circuit may only cause local overheating, while a severe one may lead to winding burnout or even transformer explosion.
• Winding Grounding: It refers to the damage of insulation between the winding and the iron core or oil tank, resulting in a conductive path between the winding and the ground. Winding grounding faults usually trigger the action of protection devices, causing the transformer to trip.
• Winding Wire Breakage: It refers to the breakage of winding wires due to mechanical stress, overheating or corrosion, resulting in circuit interruption. Wire breakage faults will cause abnormal output voltage of the transformer and affect power supply quality.

The main characteristics of winding faults are as follows:

• Abnormal rise of transformer oil temperature, especially the significant rise of top oil temperature
• Dissolved Gas Analysis (DGA) in oil shows abnormal increase in the content of gases such as hydrogen (H₂), methane (CH₄) and ethylene (C₂H₄)
• Abnormal measured value of winding DC resistance, with increased three-phase unbalance rate
• Abnormal operation sound of the transformer, which may have a heavier “buzzing” sound or accompanied by “cracking” discharge sound

2.2 Analysis of Iron Core Faults

Iron core faults are another important type of oil-immersed transformer faults, accounting for about 15%-20% of total transformer faults. Iron core faults mainly include multi-point grounding of the iron core, iron core short circuit and other forms.

• Multi-point Grounding of Iron Core: Under normal circumstances, the transformer iron core should be grounded at only one point to avoid the formation of circulating current. When there are two or more grounding points in the iron core, a closed loop will be formed between the grounding points, generating circulating current and causing local overheating of the iron core.
• Iron Core Short Circuit: It refers to the damage of insulation between silicon steel sheets of the iron core, resulting in direct contact between adjacent silicon steel sheets and forming a short circuit. Iron core short circuit will increase eddy current loss, cause local overheating of the iron core, and may burn the iron core in severe cases.

The main characteristics of iron core faults are as follows:

• Abnormal rise of transformer oil temperature, especially the significant rise of temperature at the iron core part
• Dissolved Gas Analysis (DGA) in oil shows increase in the content of gases such as hydrogen (H₂) and methane (CH₄)
• Significant decrease in the measured value of iron core insulation resistance
• Abnormal operation sound of the transformer, which may have increased vibration noise

2.3 Analysis of Insulation Faults

Insulation faults are serious fault types of oil-immersed transformers, which directly threaten the safe operation of the transformer. Insulation faults mainly include main insulation breakdown, bushing flashover, winding insulation aging and other forms.

• Main Insulation Breakdown: It refers to the breakdown of main insulation between windings, between windings and iron core or oil tank, resulting in direct contact between conductors of different potentials. Main insulation breakdown is usually a sudden process, which will cause short-circuit current and lead to the rapid action of protection devices.
• Bushing Flashover: It refers to the discharge phenomenon on the surface or inside of the transformer bushing, which may lead to bushing insulation breakdown in severe cases. Bushing flashover is usually related to bushing surface pollution, cracks or internal insulation deterioration.
• Winding Insulation Aging: It refers to the gradual deterioration of the performance of winding insulation materials under the action of heat, electricity, mechanical stress and other factors during long-term operation. Insulation aging will lead to the decrease of insulation resistance and increase of dielectric loss, and may eventually cause insulation breakdown.

The main characteristics of insulation faults are as follows:

• Dissolved Gas Analysis (DGA) in transformer oil shows abnormal increase in the content of gases such as hydrogen (H₂), carbon monoxide (CO) and carbon dioxide (CO₂)
• Significant decrease in insulation resistance measured value, with abnormal absorption ratio or polarization index
• Significant increase in partial discharge measured value
• Discharge marks or cracks may appear on the bushing surface
• Obvious discharge sound may be heard during operation

2.4 Analysis of Oil Quality Faults

Oil quality faults are important factors affecting the performance and service life of oil-immersed transformers, mainly including excessive oil temperature, excessive gas content in oil, oil deterioration and other forms.

• Excessive Oil Temperature: It refers to the transformer operating oil temperature exceeding the specified allowable value. Excessive oil temperature will accelerate insulation aging, reduce the insulation performance of oil, and may cause damage to winding insulation in severe cases.
• Excessive Gas Content in Oil: It refers to the dissolved gas content in transformer oil exceeding the specified value, especially the excessive content of gases such as hydrogen (H₂) and oxygen (O₂). Excessive gas content in oil will reduce the insulation strength of oil and increase the risk of partial discharge.
• Oil Deterioration: It refers to the gradual deterioration of transformer oil performance due to oxidation, thermal decomposition, impurity pollution and other reasons during long-term operation. Oil deterioration will lead to the decrease of oil breakdown voltage, increase of acid value and dielectric loss, affecting the insulation and heat dissipation performance of the transformer.

The main characteristics of oil quality faults are as follows:

• Abnormal rise of transformer oil temperature, exceeding the specified operating limit
• Dissolved Gas Analysis (DGA) in oil shows abnormal gas content, especially the increase of gases such as oxygen (O₂) and carbon dioxide (CO₂)
• Abnormal physical and chemical performance indicators of oil, such as decreased breakdown voltage, increased acid value and darkened color
• Precipitates or suspensions may appear in the oil

2.5 Analysis of Accessory Faults

Accessory faults mainly refer to faults occurring in auxiliary equipment of the transformer, such as tap changers, cooling systems and protection devices, accounting for about 20%-30% of total transformer faults.

• Tap Changer Faults: They include faults of no-load tap changers and on-load tap changers. Tap changer faults are usually manifested as poor contact of contacts, inaccurate tap position, poor sealing, etc., which will cause abnormal output voltage of the transformer or burnout of the tap changer.
• Cooling System Faults: They include radiator blockage, fan faults, oil pump faults, cooling pipe leakage and other forms. Cooling system faults will cause poor heat dissipation of the transformer, increase oil temperature and accelerate insulation aging.
• Protection Device Faults: They include misoperation or refusal of protection devices such as gas relays, pressure relief valves and thermometers. Protection device faults may cause the transformer to fail to get timely protection when a fault occurs, expanding the fault scope.

The main characteristics of accessory faults are as follows:

• In case of tap changer faults, the transformer output voltage is abnormal, with three-phase voltage unbalance
• In case of cooling system faults, the transformer oil temperature rises, with abnormal operation sound of cooling equipment
• In case of protection device faults, abnormal alarm signals or protection inaction may occur

3. In-depth Analysis of Causes of Oil-immersed Transformer Faults

The formation of oil-immersed transformer faults is the result of the combined action of multiple factors. In-depth analysis of fault causes is of great significance for fault prevention and handling.

3.1 Design and Manufacturing Factors

• Design Defects: Unreasonable factors in the transformer design process are potential causes of faults. For example, insufficient insulation design margin, unreasonable heat dissipation design, insufficient mechanical strength and other problems may lead to insulation breakdown, overheating or mechanical damage of the transformer during operation.
• Material Quality Problems: The quality of materials used in the transformer directly affects its operation reliability. Poor quality of iron core silicon steel sheets, impure winding wire materials, poor performance of insulation materials, unqualified quality of insulating oil and other problems may lead to various faults of the transformer during operation.
• Manufacturing Process Defects: Process defects in the manufacturing process are important causes of transformer faults. For example, irregular winding of windings, improper insulation treatment, loose iron core lamination, poor welding quality and other problems may lead to winding deformation, insulation damage, iron core overheating and other faults of the transformer during operation.
• Inadequate Quality Control: Inadequate quality control in the manufacturing process may lead to unqualified products entering the market. For example, insufficient factory testing, substandard inspection standards and other problems may put transformers with potential defects into operation, increasing the risk of faults.

3.2 Installation and Commissioning Factors

• Installation Quality Problems: Non-standard operation during transformer installation may lead to faults. For example, uneven foundation, unstable fixation, wrong wiring, poor sealing and other problems may cause excessive vibration, partial discharge, oil leakage and other faults during transformer operation.
• Improper Insulation Treatment: Problems such as too long exposure time of the transformer body to the air, incomplete vacuum drying, improper oil filling process may lead to insulation dampness or residual air bubbles, reducing insulation performance and increasing the risk of partial discharge.
• Improper Commissioning of Protection Devices: Improper commissioning of protection devices such as gas relays, pressure relief valves and thermometers may lead to misoperation or refusal of protection, affecting the safe operation of the transformer.
• Influence of Installation Environment: The influence of the transformer installation environment is also an important factor that cannot be ignored. For example, severe pollution, high humidity, excessively high or low temperature at the installation site may accelerate the aging and damage of the transformer.

3.3 Operation and Maintenance Factors

• Overload Operation: Long-term overload operation of the transformer will cause the temperature of windings and iron core to rise, accelerate insulation aging and reduce service life. According to statistics, for every 8-10℃ increase in transformer operating temperature, the insulation aging rate is approximately doubled.
• Inadequate Maintenance of Cooling System: The cooling system is the key to transformer heat dissipation. If the cooling system is not properly maintained, such as radiator blockage, fan faults, oil pump failure, it will cause poor heat dissipation of the transformer, increase oil temperature and increase the risk of faults.
• Inadequate Maintenance of Oil Quality: Transformer oil is an important medium for insulation and cooling. If the oil quality is not properly maintained, such as not conducting regular testing, not handling oil deterioration in time, not changing oil according to the specified cycle, it will lead to the decrease of oil insulation performance and accelerate insulation aging.
• Inadequate Regular Maintenance: Regular maintenance of the transformer is an important means to detect and handle potential faults. If regular maintenance is inadequate, some initial faults may not be detected and handled in time, eventually developing into serious faults.
• Untimely Handling of Abnormal Working Conditions: The transformer may encounter abnormal working conditions such as short circuit, lightning strike and overvoltage during operation. If not handled in time or properly, it may cause damage to the transformer.

3.4 Environmental and External Factors

• Influence of Atmospheric Environment: Factors such as pollution, humidity, temperature and altitude in the atmospheric environment will all affect the operation of the transformer. For example, transformer bushings in severely polluted areas are prone to flashover; high humidity environment will increase the risk of insulation dampness; extreme temperature will affect the heat dissipation and insulation performance of the transformer.
• Influence of Natural Disasters: Natural disasters such as earthquakes, floods, lightning strikes and typhoons may directly damage the transformer or destroy its operating environment, leading to transformer faults. For example, lightning strikes may cause overvoltage and break down the transformer insulation; floods may cause water inflow into the transformer and damage the insulation.
• Influence of External Short Circuit: When a short circuit fault occurs at the transformer outlet or in the nearby area, huge short-circuit current and electrodynamic force will be generated, which may cause winding deformation and insulation damage. The heat generated by the short-circuit current may also cause the winding temperature to rise sharply and damage the insulation.
• Influence of Electromagnetic Interference: Electromagnetic interference around may affect the normal operation of the transformer, especially the control of on-load tap changers and protection devices.

3.5 Insulation Aging and Service Life Factors

• Natural Aging Process: Transformer insulation materials will undergo natural aging under the action of heat, electricity, mechanical stress and other factors during long-term operation. Insulation aging will lead to the gradual decline of insulation performance, and may eventually cause insulation breakdown faults.
• Inadequate Service Life Management: The service life of the transformer is limited. If the service life is not properly managed, such as over-service, not conducting timely service life assessment, not carrying out technical transformation according to regulations, the risk of faults will increase.
• Aging Accelerating Factors: In addition to natural aging, some factors will accelerate insulation aging, such as long-term high-temperature operation, overvoltage action, mechanical vibration. The combined action of these factors will significantly shorten the service life of the transformer.

4. Fault Diagnosis Methods and Technologies for Oil-immersed Transformers

Timely and accurate fault diagnosis is the premise and basis for handling oil-immersed transformer faults. With the development of technology, transformer fault diagnosis methods are also constantly enriched and improved.

4.1 Dissolved Gas Analysis (DGA) Technology in Oil

Basic Principle

Dissolved Gas Analysis (DGA) in oil is one of the most commonly used and effective methods for diagnosing internal faults of oil-immersed transformers at present. Its basic principle is: when faults such as overheating and discharge occur inside the transformer, insulation materials (oil-paper) will decompose, generating various gases which dissolve in the transformer oil. By analyzing the composition and content of dissolved gases in the oil, it can be judged whether there is a fault inside the transformer, as well as the type and severity of the fault.

Main Detection Gases

Dissolved Gas Analysis (DGA) in oil mainly detects seven gases: hydrogen (H₂), methane (CH₄), ethane (C₂H₆), ethylene (C₂H₄), acetylene (C₂H₂), carbon monoxide (CO) and carbon dioxide (CO₂).

Analysis Methods

Commonly used Dissolved Gas Analysis (DGA) methods in oil include:

• Characteristic Gas Method: Judge the fault type according to the content of specific gases in the oil and their change trends. For example, a significant increase in acetylene content usually indicates an arc discharge fault; high content of methane and ethylene usually indicates an overheating fault.
• Three-Ratio Method: It is a fault diagnosis method recommended by the International Electrotechnical Commission (IEC). By calculating the ratios of three groups of gas contents: C₂H₂/C₂H₄, CH₄/H₂ and C₂H₄/C₂H₆, the fault type is judged according to the ratio code.
• David Triangle Method: It is a fault diagnosis method based on a triangular coordinate system. The percentage content of three main gases is taken as the three coordinates of the triangle, and the fault type is judged according to the position of the point in the triangle.
• Improved Rogers Method: It is a fault diagnosis method based on gas content and gas production rate, which considers the absolute content of gas and relative growth rate, improving the accuracy of diagnosis.

Application Value

Dissolved Gas Analysis (DGA) technology in oil has the advantages of high detection sensitivity, early detection of internal faults, no impact on the normal operation of the transformer, and has become an important means for transformer condition monitoring and fault diagnosis.

4.2 Electrical Test Diagnosis Technology

• Insulation Resistance Measurement: It is a simple and effective method for detecting insulation status. By measuring the insulation resistance between the transformer windings and the ground, and between windings, defects such as insulation dampness, aging and local damage can be found. Insulation resistance measurement is usually carried out with a megohmmeter. During measurement, temperature and humidity should be recorded to facilitate result analysis and comparison.
• Leakage Current Measurement: It is a more sensitive method for detecting insulation status than insulation resistance measurement. By measuring the leakage current under DC voltage, some defects that are difficult to find by insulation resistance measurement can be detected. Leakage current measurement is usually carried out with a DC high-voltage generator and a microammeter.
• Dielectric Loss Factor Measurement: It is an important method for evaluating the overall insulation status. By measuring the dielectric loss factor of insulation medium under AC electric field, defects such as insulation dampness, aging and partial discharge can be found. Dielectric loss factor measurement is usually carried out with a Schering bridge or a dielectric loss tester.
• Winding DC Resistance Measurement: It is an important method for checking whether the winding connection is good and whether there is wire breakage or short circuit. By measuring the DC resistance of the winding, defects such as loose winding wire joints, winding turn-to-turn short circuits and poor contact of tap changers can be found. Winding DC resistance measurement is usually carried out with a DC resistance tester, and the unbalance rate of three-phase measured values should not exceed 2%.
• Transformation Ratio Measurement: It is an important method for checking whether the number of winding turns is correct and whether the tap changer position is correct. By measuring the transformation ratio of the transformer at each tap position, defects such as wrong number of winding turns and tap changer faults can be found. Transformation ratio measurement is usually carried out with a transformation ratio bridge or a transformation ratio tester.
• Short-Circuit Impedance Measurement: It is an important method for evaluating winding deformation. By measuring the short-circuit impedance of the transformer and comparing it with the factory value or historical data, it can be judged whether the winding is deformed or displaced. Short-circuit impedance measurement is usually carried out with a short-circuit impedance tester, and the deviation from the factory value should not exceed ±2%.

4.3 Partial Discharge Detection Technology

Hazards of Partial Discharge

Partial discharge refers to the local breakdown phenomenon occurring inside the insulation under the action of electric field. Partial discharge will gradually erode the insulation material, leading to the decline of insulation performance, and may eventually cause insulation breakdown faults. Therefore, timely detection and location of partial discharge is of great significance for preventing transformer insulation faults.

Conventional Partial Discharge Measurement

Conventional partial discharge measurement is usually carried out when the transformer is out of service. By measuring the partial discharge quantity and discharge phase distribution, the insulation status can be evaluated. Conventional partial discharge measurement is usually carried out with a partial discharge detector, and attention should be paid to eliminating external interference during measurement.

Online Partial Discharge Monitoring

Online partial discharge monitoring is the detection of partial discharge when the transformer is in operation, which can monitor the insulation status of the transformer in real time. Online partial discharge monitoring usually adopts multiple detection methods such as high-frequency current sensors, ultra-high frequency sensors and ultrasonic sensors to realize multi-dimensional and all-round monitoring.

Partial Discharge Location Technology

Partial discharge location is a technology to determine the location of partial discharge sources, which is of great guiding significance for fault diagnosis and maintenance. Common partial discharge location technologies include time difference method, direction method, area location method, etc. In recent years, partial discharge accurate location technology based on multi-sensor fusion has been widely used.

Ultra-High Frequency Partial Discharge Detection

Ultra-high frequency partial discharge detection is a new type of partial discharge detection technology, which uses electromagnetic wave signals in the ultra-high frequency band (300MHz-3GHz) for detection. It has the advantages of strong anti-interference ability and high location accuracy. Ultra-high frequency partial discharge detection technology is especially suitable for online monitoring and on-site detection.

4.4 Fluorescent Optical Fiber Detection Technology

4.4.1 Basic Principle of Fluorescent Optical Fiber Detection

4.4.2 Application of Fluorescent Optical Fiber Detection in Transformers

• Winding Hot Spot Monitoring: Embed fluorescent optical fiber probes at key positions of the winding (such as the middle and end of the high-voltage winding) to monitor the temperature of winding conductors in real time. Abnormal temperature rises here usually indicate faults such as turn-to-turn short circuits or poor conductor contact.
• Iron Core Temperature Monitoring: Attach probes to iron core laminations, especially at joints and areas prone to multi-point grounding. Excessive local temperature in the iron core may signal insulation damage between laminations or residual magnetic flux concentration.
• Tap Changer Contact Monitoring: Install probes near the dynamic and static contacts of on-load tap changers. Temperature spikes at contacts often reflect poor contact (e.g., oxidized or contaminated contacts) or incomplete switching, which can lead to arcing if left unaddressed.
• Cooling System Efficiency Monitoring: Place probes at the oil inlet/outlet of radiators or cooling pipes to track the temperature difference of transformer oil before and after cooling. A reduced temperature difference may indicate blockages in cooling pipes or faulty fans/pumps.

4.4.3 Key Technical Points for Fluorescent Optical Fiber Detection

1. Sensor Material Selection: Choose fluorescent probes and optical fibers that are high-temperature resistant (≥150℃) and oil-resistant (compatible with transformer oil). Common materials include ceramic-coated fluorescent powder (for probes) and perfluorinated polymer optical fibers (for transmission), which avoid material degradation or signal attenuation in long-term immersion.
2. Installation Process Control: During probe installation, ensure close contact between the probe and the monitored surface (e.g., use heat-conducting silicone to enhance thermal transfer) to prevent temperature measurement errors caused by air gaps. Avoid excessive bending of optical fibers (bending radius ≥20mm) to prevent signal loss.
3. Signal Calibration: Regularly calibrate the detection system using a standard temperature source (e.g., a high-precision thermostatic bath) to correct deviations in fluorescence lifetime/intensity caused by long-term use (e.g., aging of fluorescent powder). Calibration intervals are typically 6–12 months.
4. Interference Suppression: Although optical fibers are EMI-resistant, ambient light (e.g., sunlight or equipment indicator lights) may interfere with fluorescence signals. Use light-shielding sleeves for optical fibers and add optical filters in the signal processor to isolate the excitation light wavelength from ambient light.
5. Data Fusion Analysis: Combine fluorescent optical fiber temperature data with other monitoring data (e.g., DGA results or partial discharge signals) for comprehensive fault diagnosis. For example, a sudden rise in winding temperature accompanied by increased acetylene (C₂H₂) in oil strongly indicates an internal arcing fault.

5. Solutions for Main Faults of Oil-immersed Transformers

Corresponding solutions should be adopted for different fault types of oil-immersed transformers to ensure the safe and reliable operation of the transformer.

5.1 Solutions for Winding Faults

Handling of Winding Turn-to-turn Short Circuit

• Slight turn-to-turn short circuit: If the short-circuit point is easily accessible, the transformer oil tank can be opened after power failure, the short-circuit point can be found, the short-circuited turns can be isolated with insulating materials, and the insulation can be strengthened. After handling, tests such as insulation resistance, winding DC resistance and partial discharge should be carried out to ensure that the fault is eliminated.
• Severe turn-to-turn short circuit: If there are many short-circuit points or they are difficult to access, the entire winding should be considered for replacement. Winding replacement is a complex work that requires professional technology and equipment, and is usually undertaken by transformer manufacturers or professional maintenance units. After winding replacement, comprehensive tests such as insulation resistance, winding DC resistance, transformation ratio, short-circuit impedance and partial discharge should be carried out.
• Preventive measures: To prevent winding turn-to-turn short circuits, the quality control of winding manufacturing should be strengthened to avoid insulation damage; the winding DC resistance should be tested regularly to detect potential problems in time; long-term overload operation of the transformer should be avoided to prevent insulation aging.

Handling of Winding Grounding Faults

• Winding grounding faults usually require power failure for handling. First, the location of the grounding point should be determined. For high-voltage winding grounding, high-voltage DC method or AC withstand voltage method can be used for location; for low-voltage winding grounding, low-voltage AC method or bridge method can be used for location.
• After finding the grounding point, the insulation damage should be checked. If the insulation damage is not serious, the grounding point can be cleaned and the insulation can be strengthened; if the insulation damage is serious, the winding or related insulation components should be considered for replacement.
• After handling, tests such as insulation resistance, leakage current and withstand voltage test should be carried out to ensure that the grounding fault is eliminated.
• Preventive measures: The quality control of winding insulation should be strengthened to avoid insulation damage; the winding insulation resistance should be tested regularly to detect insulation defects in time; water inflow and dampness of the transformer should be prevented to avoid the decline of insulation performance.

Handling of Winding Wire Breakage Faults

• Winding wire breakage faults require power failure for handling. First, the location of the wire breakage point should be determined, which can usually be located by methods such as visual inspection and winding DC resistance measurement.
• After finding the wire breakage point, corresponding handling measures should be taken according to the wire breakage situation. If there is no serious burn at the wire breakage end, the broken end can be cleaned, reconnected and the insulation can be strengthened; if there is serious burn at the wire breakage end or the wire breakage location is difficult to handle, part of the winding or the entire winding should be considered for replacement.
• After handling, tests such as winding DC resistance and insulation resistance should be carried out to ensure that the wire breakage fault is eliminated.
• Preventive measures: The quality control of winding manufacturing should be strengthened to avoid wire damage; the transformer should be prevented from being subjected to short-circuit impact to reduce mechanical stress; the winding connection parts should be checked regularly to ensure firm connection.

5.2 Solutions for Iron Core Faults

Handling of Iron Core Multi-point Grounding Faults

• Iron core multi-point grounding faults are usually manifested as a decrease in iron core insulation resistance, which may cause local overheating of the iron core in severe cases. The key to handling iron core multi-point grounding faults is to find the grounding points and eliminate the redundant grounding points.
• For slight iron core multi-point grounding faults, after the transformer is powered off, the iron core can be disconnected from the ground, and the insulation resistance between the iron core and the ground can be measured point by point with a megohmmeter to find and eliminate the grounding points. Methods for eliminating grounding points include grinding rust spots, removing foreign objects, replacing insulation gaskets, etc.
• For more serious iron core multi-point grounding faults, it may be necessary to lift the core for inspection to directly observe whether there are metal foreign objects, insulation damage and other conditions on the iron core surface. If grounding points are found, corresponding handling measures can be taken, such as removing foreign objects, repairing insulation, strengthening insulation, etc.
• After handling, the iron core insulation resistance should be measured to ensure that the iron core is grounded at a single point and the insulation resistance meets the requirements. For large transformers, the iron core grounding current should also be measured to ensure that the grounding current is within the specified range (usually not exceeding 0.1A).
• Preventive measures: The quality control during transformer manufacturing and maintenance should be strengthened to avoid metal foreign objects entering the transformer; the iron core insulation resistance and grounding current should be tested regularly to detect potential problems in time; the transformer should be prevented from being subjected to short-circuit impact to reduce the impact of mechanical vibration on the iron core insulation.

Handling of Iron Core Short Circuit Faults

• Iron core short circuit faults usually refer to the damage of insulation between silicon steel sheets of the iron core, resulting in direct contact between adjacent silicon steel sheets and forming a short circuit. Iron core short circuit will increase eddy current loss and cause local overheating of the iron core.
• Handling iron core short circuit faults usually requires lifting the core for inspection to directly observe whether there are insulation damage, short circuit points and other conditions on the iron core silicon steel sheets. For slight insulation damage, the short circuit points can be eliminated, insulating paint can be coated to restore the insulation between silicon steel sheets; for more serious insulation damage, part of the silicon steel sheets or the entire iron core may need to be replaced.
• After handling, tests such as iron core insulation resistance measurement and no-load loss measurement should be carried out to ensure that the iron core short circuit fault is eliminated.
• Preventive measures: The quality control of iron core manufacturing should be strengthened to ensure that the surface insulation of silicon steel sheets is intact; the transformer should be prevented from being subjected to short-circuit impact to reduce the impact of mechanical vibration on the iron core insulation; long-term overload operation of the transformer should be avoided to prevent insulation aging caused by iron core overheating.

5.3 Solutions for Insulation Faults

Handling of Main Insulation Breakdown

• Main insulation breakdown is a serious fault, which usually causes the transformer to trip and requires power failure for handling. First, the location of the breakdown point should be determined. For insulation breakdown between the high-voltage winding and the iron core or oil tank, high-voltage DC method or AC withstand voltage method can be used for location; for insulation breakdown between high-voltage and low-voltage windings, methods such as insulation resistance measurement and dielectric loss measurement can be used for location.
• After finding the breakdown point, corresponding handling measures should be taken according to the insulation damage situation. For slight insulation damage, the breakdown point can be cleaned and the insulation can be strengthened; for serious insulation damage, the relevant insulation components or the entire winding should be considered for replacement.
• After handling, tests such as insulation resistance, leakage current and withstand voltage test should be carried out to ensure that the insulation performance is restored.
• Preventive measures: The quality control of insulation materials should be strengthened to avoid insulation defects; the insulation performance should be tested regularly to detect potential problems in time; long-term overload operation of the transformer should be avoided to prevent insulation aging; overvoltage protection devices such as lightning arresters should be installed to prevent insulation breakdown caused by overvoltage.

Handling of Bushing Flashover

• Handling of bushing flashover faults should take different measures according to the severity of flashover. For slight surface flashover, the bushing surface can be cleaned after power failure, and the bushing should be checked for cracks or damage. If the bushing surface is polluted, it should be wiped clean with a clean cloth or special cleaning agent; if there are slight cracks on the bushing surface, insulating paint or silicone rubber coating can be coated; if there are serious cracks or damage on the bushing surface, the bushing should be replaced.
• For internal flashover of the bushing, the bushing usually needs to be replaced. Bushing replacement is a work with high technical requirements, which requires professional technology and equipment. After bushing replacement, tests such as insulation resistance, dielectric loss and withstand voltage should be carried out to ensure that the bushing performance meets the requirements.
• Preventive measures: The bushing surface should be cleaned regularly to prevent pollution flashover; the bushing should be checked regularly for cracks or damage to detect potential problems in time; anti-pollution flashover coatings or creepage extenders should be installed to improve the anti-pollution flashover ability of the bushing; in severely polluted areas, anti-pollution type bushings or composite insulation bushings can be considered.

Handling of Winding Insulation Aging

• Handling of winding insulation aging should take different measures according to the aging degree. For slight aging, the oil quality management can be strengthened, and oil treatment can be carried out regularly to slow down the aging speed; for serious aging, the winding insulation or the entire winding should be considered for replacement.
• Handling of winding insulation aging usually requires lifting the core for inspection to evaluate the insulation aging degree. For windings with serious insulation aging, replacing the insulation is the most thorough solution. Insulation replacement is a complex work that requires professional technology and equipment, and is usually undertaken by transformer manufacturers or professional maintenance units.
• After handling, tests such as insulation resistance, dielectric loss and partial discharge should be carried out to ensure that the insulation performance is restored.
• Preventive measures: Long-term overload operation of the transformer should be avoided to control the transformer operating temperature; the transformer oil quality should be tested regularly to handle oil deterioration in time; online monitoring devices should be installed to monitor the transformer operating status in real time; for transformers with long service life, insulation monitoring and evaluation should be strengthened to detect insulation aging problems in time.

5.4 Solutions for Oil Quality Faults

Handling of Excessive Oil Temperature

• Handling of excessive oil temperature should first determine the cause, and then take corresponding measures. If it is caused by excessive load, the load should be adjusted to avoid long-term overload operation of the transformer; if it is caused by cooling system faults, the cooling system should be checked, and the faulty components should be repaired or replaced; if it is caused by excessively high ambient temperature, heat dissipation measures can be increased, such as adding fans and improving ventilation conditions.
• For transformers with excessive oil temperature, monitoring should be strengthened and the oil temperature change should be recorded. If the oil temperature continues to be too high, the load should be reduced or the transformer should be shut down to prevent insulation damage.
• Preventive measures: The transformer capacity should be reasonably configured to avoid long-term overload operation; the cooling system should be checked regularly to ensure its normal operation; the transformer installation environment should be improved to ensure good ventilation conditions; oil temperature monitoring devices should be installed to monitor the oil temperature change in real time.

Handling of Excessive Gas Content in Oil

• Handling of excessive gas content in oil usually adopts vacuum degassing treatment. Vacuum degassing treatment is to heat the transformer oil under vacuum conditions to make the gases in the oil escape, and then extract the gases through a vacuum pump. Vacuum degassing treatment can effectively reduce the gas content in the oil and improve the insulation performance of the oil.
• For transformers in operation, online vacuum oil filters can be used for degassing treatment; for transformers out of service, offline vacuum oil filters can be used for degassing treatment. After treatment, the gas content in the oil should be tested to ensure that the gas content meets the standard requirements.
• Preventive measures: The transformer sealing management should be strengthened to prevent air from entering; the gas content in the oil should be tested regularly to detect problems in time; long-term contact between the transformer oil and air should be avoided to reduce gas dissolution; oil conservators and breathers should be installed to prevent direct contact between the oil and air.

Handling of Oil Deterioration

• Handling of oil deterioration should take different measures according to the deterioration degree. For slight deterioration, methods such as filtration and adsorption can be used for regeneration treatment to remove impurities, moisture and acidic substances in the oil; for serious deterioration, new oil should be considered for replacement.
• Filtration treatment is to remove solid impurities and moisture in the oil through an oil filter to improve the oil cleanliness. Adsorption treatment is to use adsorbents (such as silica gel, activated alumina, etc.) to adsorb acidic substances, colloids, pigments and other substances in the oil to improve the oil performance. Regeneration treatment can be carried out when the transformer is in operation or out of service.
• Replacing new oil is an effective method for handling serious oil deterioration. When replacing new oil, the old oil in the transformer should be completely drained, and the inside of the transformer should be flushed with new oil to ensure internal cleanliness. After replacing new oil, the oil quality should be tested to ensure that the oil quality meets the standard requirements.
• Preventive measures: The oil quality management should be strengthened, and the oil quality should be tested regularly to detect problems in time; long-term overload operation of the transformer should be avoided to prevent accelerated oil deterioration; water inflow and dampness of the transformer should be prevented to avoid oil deterioration; oil protection devices such as oil purifiers and oil conservator breathers should be installed to slow down the oxidation and deterioration of the oil.

5.5 Solutions for Accessory Faults

Handling of Tap Changer Faults

• Poor contact of tap changer contacts: If the poor contact is caused by oxidation or dirt on the contact surface, the tap changer can be opened after power failure, the contact surface can be cleaned, the oxide layer can be polished, the contact pressure can be adjusted to ensure good contact. After handling, the winding DC resistance should be measured to ensure that the contact resistance of the contacts meets the requirements.
• Poor sealing of tap changers: If the poor sealing is caused by aging or damage of sealing parts, the sealing parts should be replaced. When replacing sealing parts, attention should be paid to selecting appropriate materials, such as oil-resistant rubber sealing parts (such as nitrile rubber), and standardizing the installation process to ensure the sealing effect. After handling, the tap changer should be checked for oil leakage.
• Mechanical faults of tap changers: If the fault is caused by damage or jamming of tap changer mechanical components, the mechanical components should be checked, and the damaged components should be repaired or replaced. After handling, the tap changer action test should be carried out to ensure that the tap changer acts flexibly and in place.
• On-load tap changer faults: On-load tap changers are complex equipment, and their fault handling usually requires professional technology and equipment. For on-load tap changer faults, it is recommended to be handled by professional maintenance units. After handling, tests such as tap changer action characteristic test and transition resistance test should be carried out to ensure that the tap changer performance meets the requirements.
• Preventive measures: The quality control of tap changer manufacturing should be strengthened to ensure good contact of contacts; the contact resistance of tap changer contacts should be checked regularly to detect potential problems in time; the sealing condition of tap changers should be checked regularly to prevent oil leakage; the tap changer operation should be standardized to avoid frequent switching; online monitoring devices should be installed on on-load tap changers to monitor the tap changer status in real time.

Handling of Cooling System Faults

• Radiator blockage: If the radiator is blocked externally, the dust and debris on the radiator surface can be cleaned with high-pressure water gun or compressed air after power failure; if the radiator is blocked internally, chemical cleaning or high-pressure water flushing methods should be used for cleaning. After cleaning, the heat dissipation effect of the radiator should be checked to ensure normal heat dissipation.
• Fan faults: If the fan motor is damaged, the motor should be replaced; if the fan blades are damaged, the blades should be replaced; if the fan control circuit is faulty, the control circuit should be checked, and the faulty components should be repaired or replaced. After handling, the fan operation test should be carried out to ensure that the fan operates normally.
• Oil pump faults: If the oil pump motor is damaged, the motor should be replaced; if the oil pump impeller is damaged, the impeller should be replaced; if the oil pump sealing is poor, the sealing parts should be replaced. After handling, the oil pump operation test should be carried out to ensure that the oil pump operates normally and the oil pressure meets the requirements.
• Cooling pipe leakage: If the cooling pipe leaks at the weld, welding repair or sealing with polymer materials can be used; if the cooling pipe is corroded and perforated, the cooling pipe should be replaced. After handling, the pressure test should be carried out to ensure that the cooling pipe has no leakage.
• Preventive measures: The radiator should be cleaned regularly to ensure the heat dissipation effect; the operation status of fans and oil pumps should be checked regularly to detect and handle faults in time; the sealing condition of the cooling system should be checked regularly to prevent leakage; the maintenance management of the cooling system should be strengthened and a detailed maintenance plan should be formulated; temperature monitoring devices should be installed on the cooling system to monitor the cooling effect in real time.

Handling of Protection Device Faults

• Gas relay faults: If the gas relay malfunctions, it should be checked whether the setting of the gas relay is correct, whether the secondary circuit is faulty, and whether there is a slight fault inside the transformer; if the gas relay refuses to act, it should be checked whether the gas relay is jammed, whether the secondary circuit is broken, and whether the heavy gas trip connecting piece is put into use. After handling, the gas relay should be calibrated to ensure that its action characteristics meet the requirements.
• Pressure relief valve faults: If the pressure relief valve malfunctions, it should be checked whether the set pressure of the pressure relief valve is correct and whether the secondary circuit is faulty; if the pressure relief valve refuses to act, it should be checked whether the pressure relief valve is jammed and whether the valve core is rusted. After handling, the pressure relief valve should be calibrated to ensure that its action pressure meets the requirements.
• Thermometer faults: If the thermometer indication is inaccurate, it should be checked whether the thermometer sensor is damaged, whether the secondary circuit is faulty, and whether the indicating instrument is calibrated. After handling, the thermometer should be calibrated to ensure accurate indication.
• Preventive measures: The regular calibration and maintenance of protection devices should be strengthened to ensure their accurate and reliable action; the secondary circuit of protection devices should be checked regularly to ensure firm wiring and no looseness or short circuit; online monitoring devices should be installed on protection devices to monitor the status of protection devices in real time; the training of operation and maintenance personnel should be strengthened to improve their operation and maintenance level of protection devices.

6. Fault Prevention and Maintenance Strategies for Oil-immersed Transformers

Preventing transformer faults is the key to ensuring the safe and reliable operation of transformers, and comprehensive and multi-level prevention and maintenance strategies should be adopted.

6.1 Preventive Measures in the Design and Manufacturing Stage

Optimizing the Design Scheme

• In the transformer design stage, insulation materials, winding structures and cooling methods should be reasonably selected according to the use environment and load characteristics to ensure that the transformer has sufficient insulation margin and heat dissipation capacity.
• For special environmental conditions (such as high temperature, high humidity, pollution, etc.), corresponding protective designs should be adopted, such as strengthening insulation, increasing heat dissipation area, and adopting anti-pollution flashover measures.
• Factors facilitating maintenance and overhaul should be considered in the design, such as setting necessary maintenance channels, maintenance holes, sampling valves, etc., to facilitate future maintenance and overhaul.

Improving Manufacturing Quality

• The quality control of raw materials should be strengthened to ensure that the used silicon steel sheets, wires, insulation materials, transformer oil and other materials meet the standard requirements.
• The manufacturing process specifications should be strictly implemented to ensure the quality of key processes such as winding, iron core assembly, insulation treatment and general assembly.
• The quality inspection in the manufacturing process should be strengthened to strictly control each process and detect and eliminate manufacturing defects in time.
• The factory test items and standards should be improved to ensure that each transformer undergoes strict tests and all performance indicators meet the requirements.

Adopting Advanced Technologies and Materials

• High-quality insulation materials and wires should be adopted to improve the electrical and mechanical performance of windings.
• Vacuum drying and vacuum oil filling processes should be adopted to reduce air gaps and moisture in insulation and improve insulation performance.
• On-line oil filtering devices for on-load tap changers should be adopted to extend the service life of tap changer oil.
• Intelligent components and online monitoring devices should be adopted to realize real-time monitoring and fault early warning of transformer status.

6.2 Preventive Measures in the Installation and Commissioning Stage

Ensuring Installation Quality

• The transformer installation should be carried out in strict accordance with the design requirements and installation specifications to ensure a flat foundation, stable fixation and correct wiring.
• The exposure time of the transformer body to the air should be strictly controlled to avoid insulation dampness. For large transformers, the exposure time of the body should generally not exceed 16-24 hours (varies with ambient humidity).
• The transformer should be tightly sealed, and qualified gaskets should be used at all flange connections, and the bolts should be tightened evenly to prevent oil leakage.
• The installation of the cooling system should meet the design requirements to ensure correct connection of cooling pipelines and no blockage or leakage.

Standardizing the Commissioning Process

• After the transformer installation is completed, comprehensive commissioning and tests should be carried out, including insulation resistance, winding DC resistance, transformation ratio, short-circuit impedance, no-load loss, load loss and other tests, to ensure that all indicators meet the requirements.
• The commissioning of protection devices should be carried out in strict accordance with the design requirements to ensure correct protection setting values and sensitive and reliable action. Protection devices such as gas relays and pressure relief valves should be calibrated to ensure that their action characteristics meet the requirements.
• The cooling system should be put into trial operation to check whether the fans, oil pumps and other equipment operate normally and whether the oil temperature and oil pressure meet the requirements.
• The tap changer action test should be carried out to ensure that the tap changer acts flexibly and in place, and the contact resistance meets the requirements.

Doing a Good Job in Handover Acceptance

• After the transformer installation and commissioning are completed, strict handover acceptance should be carried out to ensure that the installation quality and commissioning results meet the requirements. Handover acceptance should include appearance inspection, installation quality inspection, test report review and other contents.
• During handover acceptance, the technical data should be carefully checked, including product qualification certificates, factory test reports, installation and operation instructions, as-built drawings, etc., to ensure the completeness and accuracy of the data.
• Problems found during acceptance should be handled in time until they meet the requirements. Transformers that have not passed acceptance or failed acceptance shall not be put into operation.

6.3 Preventive Measures in the Operation and Maintenance Stage

Reasonable Operation Management

• The transformer operation should be carried out in strict accordance with the rated parameters to avoid long-term overload operation. The transformer load should not exceed 105% of the rated capacity. In special cases where overload operation is required, the overload time and overload multiple should be controlled in accordance with relevant regulations.
• The transformer operating voltage should not exceed 105% of the rated voltage, and the maximum should not exceed 110% of the rated voltage. Excessively high operating voltage will cause iron core saturation, increase iron loss and temperature rise; excessively low operating voltage will reduce the transformer output capacity.
• The transformer operating oil temperature should be controlled within the specified range, and the top oil temperature should generally not exceed 85℃ (for Class A insulation). Excessively high oil temperature will accelerate insulation aging and reduce service life.
• The operation mode of the cooling system should be adjusted in time according to the changes of load and ambient temperature to ensure that the transformer operates under the optimal temperature conditions.

Improving Monitoring Means

• Necessary monitoring equipment should be equipped, such as thermometers, oil level gauges, gas relays, etc., to monitor the transformer operating status in real time.
• Tests such as Dissolved Gas Analysis (DGA) in oil, winding DC resistance measurement and insulation resistance measurement should be carried out regularly to detect potential problems in time.
• For important transformers, online monitoring devices should be installed to monitor parameters such as transformer oil temperature, oil level, winding temperature, partial discharge and vibration in real time, realizing fault early warning and early diagnosis.
• A transformer operation file should be established to record the transformer operation data, test data, maintenance records, etc., providing a basis for status evaluation and fault diagnosis.

Regular Maintenance and Overhaul

• The appearance of the transformer should be checked regularly, including the bushing, oil level, oil temperature, sound, oil leakage and other conditions, to detect abnormalities in time.
• The operation status of the cooling system should be checked regularly, including the operation status of fans, oil pumps, radiators and other equipment, and the dust and debris on the radiator surface should be cleaned in time.
• The operation status of the tap changer should be checked regularly, including the tap position, contact resistance of contacts, sealing condition, etc., to detect and handle potential problems in time.
• The operation status of protection devices should be checked regularly, including gas relays, pressure relief valves, thermometers, etc., to ensure sensitive and reliable action of protection devices.
• Oil quality testing and treatment should be carried out regularly, including tests such as Dissolved Gas Analysis (DGA) in oil, oil breakdown voltage, acid value and dielectric loss, to detect oil deterioration problems and handle them in time.
• Electrical tests should be carried out regularly, including insulation resistance, winding DC resistance, transformation ratio, short-circuit impedance, no-load loss and other tests, to evaluate the electrical performance of the transformer.

Strengthening Fault Management

• A sound fault management system should be established to record and analyze transformer faults in a timely and accurate manner, and summarize fault rules and lessons.
• Slight faults should be handled in time to prevent them from developing into serious faults; detailed handling plans should be formulated for serious faults to ensure handling quality.
• Comprehensive tests and inspections should be carried out after fault handling to ensure that the fault is eliminated and the transformer performance is restored.
• Corresponding preventive measures should be taken according to the fault analysis results to prevent similar faults from occurring again.

6.4 Condition-based Maintenance Strategy for Oil-immersed Transformers

Condition-based Maintenance Concept

• Condition-based maintenance is a maintenance method based on equipment status and aimed at predicting equipment faults. Compared with traditional periodic maintenance, condition-based maintenance can more accurately grasp the maintenance timing, improve the pertinence and effectiveness of maintenance, and reduce unnecessary maintenance work.
• The premise of implementing condition-based maintenance is to establish a sound condition monitoring system, obtain transformer status information through various monitoring means, and evaluate the health status of the transformer.
• Condition-based maintenance should formulate differentiated maintenance strategies according to factors such as the importance of the transformer, operating environment and historical status, so as to realize the optimal allocation of maintenance resources.

Condition Evaluation Methods

• Condition evaluation based on Dissolved Gas Analysis (DGA) in oil: Judge whether there is a fault inside the transformer and the type and severity of the fault by analyzing the composition and content of dissolved gases in the oil.
• Condition evaluation based on electrical tests: Evaluate the electrical performance and insulation status of the transformer through test data such as insulation resistance, winding DC resistance, transformation ratio, short-circuit impedance and dielectric loss.
• Condition evaluation based on partial discharge detection: Evaluate the overall insulation status and local defects by detecting the partial discharge quantity and discharge characteristics.
• Condition evaluation based on infrared thermography detection: Detect local overheating defects inside by detecting the temperature distribution on the transformer surface.
• Condition evaluation based on vibration analysis: Evaluate the mechanical status of windings and iron core by detecting the transformer vibration signal.
• Condition evaluation based on multi-source information fusion: Conduct comprehensive analysis of various monitoring and test data to realize comprehensive and accurate evaluation of transformer status.

Maintenance Decision Support

• A transformer condition evaluation index system should be established to quantitatively evaluate various status parameters of the transformer and determine the health level of the transformer.
• Corresponding maintenance strategies should be formulated based on the condition evaluation results: for transformers in good health status, the maintenance cycle can be appropriately extended; for transformers with potential problems, monitoring should be strengthened and maintenance should be arranged in a timely manner; for transformers with existing faults, maintenance or replacement should be arranged in a timely manner.
• Artificial intelligence technologies such as neural networks, expert systems and fuzzy theory should be used to establish transformer fault diagnosis and maintenance decision models to provide support for maintenance decisions.
• A transformer maintenance knowledge base should be established to collect and organize various fault cases and maintenance experiences to provide reference for maintenance decisions.

7. Latest Progress in Oil-immersed Transformer Fault Research

With the continuous development of power technology, a series of new progresses have been made in oil-immersed transformer fault research, providing new methods and means for transformer fault diagnosis and handling.

7.1 New Fault Diagnosis Technologies

Fault Diagnosis Based on Deep Learning

• Deep learning is a machine learning technology based on neural networks, which can automatically learn features and rules from a large amount of data and has strong pattern recognition ability. In recent years, deep learning has been widely used in the field of transformer fault diagnosis.
• Transformer fault diagnosis methods based on deep learning usually take the content of dissolved gases in oil, electrical test data, partial discharge signals, etc. as input, and the fault type as output, and establish the mapping relationship between input and output through the training of a large number of sample data.
• Studies have shown that fault diagnosis methods based on deep learning have obvious advantages in accuracy and reliability, and can effectively improve the accuracy and efficiency of fault diagnosis.

Fault Diagnosis Based on Multi-sensor Fusion

• Multi-sensor fusion is to comprehensively analyze the data obtained by various types of sensors (such as dissolved gas sensors in oil, partial discharge sensors, temperature sensors, vibration sensors, etc.) to realize the comprehensive evaluation of transformer status.
• Multi-sensor fusion diagnosis technology can make full use of the advantages of various sensors and improve the accuracy and reliability of diagnosis. For example, combining Dissolved Gas Analysis (DGA) in oil with partial discharge monitoring can more comprehensively evaluate the transformer insulation status; combining temperature monitoring with vibration analysis can more accurately judge the mechanical status of windings and iron core.
• Multi-sensor fusion diagnosis technology usually adopts multiple fusion methods such as data-level fusion, feature-level fusion and decision-level fusion to realize multi-level and all-round evaluation of transformer status.

Fault Diagnosis Based on Big Data and Cloud Computing

• Big data and cloud computing technologies provide new ideas and methods for transformer fault diagnosis. By collecting and analyzing a large amount of transformer operation data, test data, maintenance data, etc., the rules and trends of transformer faults can be found, realizing fault prediction and early diagnosis.
• A transformer fault diagnosis system based on big data and cloud computing is usually composed of a data acquisition layer, a data processing layer, a data analysis layer and an application layer, which can realize real-time collection, storage, processing and analysis of data, providing support for transformer condition evaluation and fault diagnosis.
• A transformer fault diagnosis system based on big data and cloud computing can realize cross-regional and cross-equipment data analysis and comparison, find abnormalities of individual transformers and common problems of group transformers, providing reference for transformer fault diagnosis and prevention.

7.2 New Insulation Materials and Technologies

Nano-composite Insulation Materials

• Nano-composite insulation materials are new composite materials formed by dispersing nano-scale fillers into traditional insulation materials. Nano-composite insulation materials have excellent electrical performance, thermal performance and mechanical performance, which can effectively improve the insulation level and service life of transformers.
• Common nano-fillers include nano-SiO₂, nano-Al₂O₃, nano-TiO₂, etc. These nano-fillers can improve the corona resistance, partial discharge resistance and thermal conductivity of insulation materials, and improve the service life of insulation materials.
• Nano-composite insulation materials have broad application prospects in transformer winding insulation, bushing insulation, tap changer insulation and other aspects, and can improve the reliability and service life of transformers.

High Flash Point Insulating Oil

• High flash point insulating oil is a type of transformer oil with a flash point higher than 300℃, which has good fire resistance and insulation performance. High flash point insulating oil can effectively reduce the risk of transformer fire and explosion, and is especially suitable for places with high fire protection requirements.
• Common high flash point insulating oils include silicone oil, ester oil, synthetic hydrocarbon oil, etc. These high flash point insulating oils have excellent oxidation stability, thermal stability and electrical performance, and can extend the service life of transformers.
• The application of high flash point insulating oil can reduce the maintenance workload and operation cost of transformers, and improve the safety and reliability of transformers.

Environmentally Friendly Insulation Materials

• Environmentally friendly insulation materials are insulation materials that are environmentally friendly, degradable or recyclable. With the enhancement of environmental protection awareness, the application of environmentally friendly insulation materials in transformers has received more and more attention.
• Environmentally friendly insulation materials include degradable cellulose materials, recyclable synthetic materials, etc. These materials have good electrical performance and mechanical performance, and have less impact on the environment at the same time.
• The application of environmentally friendly insulation materials can reduce the impact of transformers on the environment and meet the requirements of sustainable development.

7.3 Intelligent Operation and Maintenance Management System

Transformer Intelligent Operation and Maintenance Platform

• The transformer intelligent operation and maintenance platform is a transformer operation and maintenance management system based on the Internet of Things, big data and artificial intelligence technologies, which can realize real-time monitoring, fault diagnosis, predictive maintenance and full life cycle management of transformer status.
• The transformer intelligent operation and maintenance platform is usually composed of a perception layer, a network layer and an application layer. The perception layer is responsible for collecting various status data of the transformer; the network layer is responsible for data transmission and processing; the application layer is responsible for data analysis and display, providing support for operation and maintenance decisions.
• The transformer intelligent operation and maintenance platform can realize comprehensive perception, in-depth analysis and intelligent decision-making of transformer status, improve operation and maintenance efficiency and accuracy, and reduce operation and maintenance costs and risks.

Transformer Operation and Maintenance Technology Based on Digital Twin

• Digital twin is a virtual model corresponding to a physical entity, which can reflect the status and behavior of the physical entity in real time. Transformer operation and maintenance technology based on digital twin combines the physical model, mathematical model and operation data of the transformer to establish a digital twin model of the transformer, realizing accurate simulation and prediction of the transformer status.
• Transformer operation and maintenance technology based on digital twin can realize functions such as virtual commissioning, fault simulation and service life prediction of the transformer, providing comprehensive support for the design, manufacturing, installation, operation and maintenance of the transformer.
• Transformer operation and maintenance technology based on digital twin can improve the reliability and operation efficiency of the transformer, reduce operation and maintenance costs and risks, and is an important development direction of future transformer operation and maintenance.

Remote Operation and Maintenance and Expert Diagnosis System

• The remote operation and maintenance and expert diagnosis system is a system that uses modern communication technology and computer technology to realize remote monitoring, remote diagnosis and remote guidance of transformers. This system can connect transformers scattered in different locations to a centralized monitoring center, and a team of experts will conduct unified monitoring and diagnosis.
• The remote operation and maintenance and expert diagnosis system is usually composed of a remote monitoring terminal, a communication network and an expert diagnosis center. The remote monitoring terminal is responsible for collecting transformer status data; the communication network is responsible for data transmission; the expert diagnosis center is responsible for data analysis and diagnosis, providing support for operation and maintenance decisions.
• The remote operation and maintenance and expert diagnosis system can make full use of expert resources, improve the accuracy and efficiency of fault diagnosis, reduce the blindness and workload of on-site maintenance, and is especially suitable for the operation and maintenance of transformers in remote areas and important transformers.

8. Conclusions and Prospects

8.1 Research Conclusions (Continued)

• Targeted Solutions: Corresponding solutions should be adopted for different fault types. For winding faults, measures such as repair or winding replacement should be taken according to the severity of the fault; for iron core faults, targeted treatments should be implemented for issues such as multi-point grounding or short circuits; for insulation faults, insulation repair or replacement should be carried out based on the degree of insulation damage; for oil quality faults, filtration, adsorption, or oil replacement should be used according to the degree of oil deterioration; for accessory faults, appropriate handling methods should be adopted for different accessory types.
• Importance of Preventive Measures: Preventing transformer faults is crucial for ensuring the safe and reliable operation of transformers. By strengthening quality control in design and manufacturing, ensuring installation and commissioning quality, optimizing operation management, improving monitoring methods, and conducting regular maintenance and overhaul, transformer faults can be effectively prevented, and the service life of transformers can be extended.

8.2 Future Outlook

8.2.1 Intelligent Fault Diagnosis Technologies

8.2.2 New Insulation Materials and Technologies

8.2.3 Intelligent Operation and Maintenance (O&M) Management Systems

8.2.4 Condition-Based Full-Life Cycle Management

8.2.5 Green Environmental Protection and Sustainable Development

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