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Views: 0 Author: Site Editor Publish Time: 2026-08-11 Origin: Site
Transformers play a crucial role in power systems by performing voltage conversion and power distribution, and their operating condition directly affects the reliability of power supply. Whether it is an oil-immersed transformer or a dry-type transformer, problems may occur after long-term operation. Some faults develop gradually, with only slight abnormalities in parameters at the beginning. If they are not detected in time, they may gradually worsen and eventually lead to equipment shutdown or even burnout.
For power companies, EPC contractors, and industrial customers, understanding common transformer faults, how to identify them, and how to handle them can help detect problems in time during the operation phase of a project and reduce losses caused by unplanned outages.
Zisheng Electric has been deeply involved in transformer R&D, manufacturing, and project supporting services for many years, accumulating certain fault analysis and operation & maintenance experience in different application environments. Based on common issues encountered in actual operation, this article analyzes the main types of transformer faults, diagnostic methods, and corresponding treatment measures.
From the perspective of fault location, transformer faults mainly occur in windings, cores, insulation systems, tap changers, bushings, and cooling systems. From the perspective of fault characteristics, they can be classified into electrical faults, thermal faults, mechanical faults, and oil-related faults.
The winding is one of the parts of a transformer most prone to failure. Common faults mainly include inter-turn short circuits, layer-to-layer short circuits, and winding deformation.
When an inter-turn or layer-to-layer short circuit occurs, a large circulating current will form in the short-circuited section, causing the winding temperature to rise rapidly. The symptoms include: abnormally high oil temperature, an increase in current on the power supply side, and unbalanced DC resistance between phases. In severe cases, abnormal noises may also be heard from the oil tank.
The main causes of short circuits generally include: insulation aging or moisture absorption, which reduces insulation strength; hidden problems left during manufacturing, such as damage to the inter-turn insulation itself; and impacts from short-circuit currents during operation, which cause winding deformation and subsequent insulation damage.
Winding deformation is mostly caused by electromagnetic forces generated during external short-circuit faults. After a transformer experiences an outlet short circuit or a nearby short circuit, the winding may undergo irreversible deformation. Although the transformer may continue operating at that time, the insulation may already have been damaged, making it highly likely to develop into a short circuit later.
The diagnosis of winding faults mainly relies on the following methods:
DC resistance test. Measure the DC resistance of each phase winding. If the three-phase unbalance rate exceeds the standard (generally 2%), it can basically indicate the presence of an inter-turn short circuit or poor contact.
Turns ratio test. Measure the voltage ratio at each tap position. If the deviation exceeds the allowable range, there may be an inter-turn short circuit in the winding.
Short-circuit impedance test. Changes in short-circuit impedance can indicate whether the winding has experienced deformation.
Dissolved Gas Analysis (DGA) of transformer oil. Overheating or discharge in the winding will generate specific gases. By analyzing the gas composition in the oil, the fault type and severity can be determined.
The treatment of winding faults depends on the specific fault type and severity.
For minor inter-turn short circuits, oil filtration and drying treatment can be attempted first. For serious winding faults, the transformer must be taken out of service for maintenance. The active part must be lifted out for inspection, and the damaged winding should be replaced or rewound. If winding deformation is severe, the winding or the entire transformer may need to be replaced.
For prevention: avoid long-term overload operation; perform winding deformation tests promptly after short-circuit faults occur in the system; and regularly carry out preventive tests to monitor the changing trend of winding insulation conditions.
The core is the magnetic circuit of the transformer. The main faults are multi-point grounding and local overheating.
During normal operation, the core is only allowed to have one grounding point. Once two or more grounding points appear, a closed circuit will be formed. Under an alternating magnetic field, circulating currents will be generated, causing local overheating of the core.
Another common problem is damage to the insulation between silicon steel sheets, usually caused by mechanical damage or long-term operational aging. Local short circuits between silicon steel sheets increase eddy current losses, resulting in a rise in local temperature.
The diagnostic methods for core faults include:
Grounding current measurement. Install an ammeter in series with the core grounding line. A significant increase in measured current indicates a possible multi-point grounding fault.
Dissolved Gas Analysis (DGA) of transformer oil. Core overheating generates characteristic gases, and DGA can determine whether the core has experienced overheating.
Partial discharge detection. Multi-point grounding of the core is often accompanied by partial discharge, which can be used as an auxiliary confirmation method.
For multi-point grounding of the core, a current-limiting resistor can be temporarily connected in the grounding circuit to limit the grounding current. Ultimately, the transformer must be taken out of service for maintenance. The active part should be lifted out, the core grounding condition inspected, and unnecessary grounding points removed.
If the insulation between silicon steel sheets is damaged, the active part also needs to be lifted out. The damaged areas should be repaired with insulation treatment, or the damaged silicon steel sheets should be replaced.
The insulation system is the key to the long-term reliable operation of a transformer. The main insulation-related faults are insulation aging and insulation moisture absorption.
Insulation aging. This is an unavoidable issue during operation. Under the combined effects of electrical, thermal, mechanical, and environmental factors, the performance of insulation gradually deteriorates over time. The aging rate is directly related to operating temperature. According to thermal aging principles, the service life of insulation materials decreases significantly as operating temperature increases. In engineering design, relevant thermal aging models are usually referenced for evaluation. DGA can detect characteristic gases generated during the aging process.
Insulation moisture absorption. This is a major cause of sudden deterioration in insulation performance. The insulation system mainly includes winding insulation, inter-layer insulation, and inter-turn insulation. Long-term high-temperature operation accelerates the aging of insulation materials, reducing their mechanical strength and electrical performance. Common causes of moisture absorption include: aging or damage of sealing components, a low oil level that increases the contact area between insulating oil and air, and failure of the breather to prevent moisture from entering.
Insulation resistance test. Use a megohmmeter to measure the insulation resistance between windings and ground as well as between windings. A significantly low resistance value indicates that the insulation may have absorbed moisture or aged.
Dielectric loss factor (tanδ) test. Measure the dielectric loss factor of the insulation material. An increase in value indicates a decline in insulation performance.
Moisture analysis in oil. Measure the water content in the insulating oil. The acceptable moisture level should be evaluated according to the equipment voltage level and operating condition. High-voltage equipment generally has stricter moisture requirements. Excessive moisture indicates that the insulation system has absorbed water.
Oil quality test. This includes breakdown voltage testing, acid value measurement, and interfacial tension measurement, which can comprehensively evaluate the condition of insulating oil.
For insulation moisture absorption, vacuum drying treatment can be carried out to remove moisture from the insulation materials. Pressure vacuum oil filtration can also effectively remove water and gases from the insulating oil.
If insulation aging is severe, oil replacement or insulating oil regeneration treatment is required. In extreme cases, aged insulation materials must be replaced.
The key prevention measures are: regularly performing insulation performance tests and establishing a trend analysis of insulation condition changes; maintaining the sealing system in good condition to prevent moisture ingress; ensuring the breather operates properly and replacing desiccant regularly.
The tap changer is one of the transformer components with a relatively high failure rate. Common problems include poor contact of contacts, contact erosion, and switching mechanism failures.
When poor contact occurs, the contact resistance increases, causing severe local heating. Over time, the contacts may become burned or even welded together. Symptoms include: increased oil temperature, abnormal output voltage, and increased DC resistance unbalance.
The main causes include: insufficient contact spring pressure, resulting in poor contact; oxidation or contamination on the contact surface, increasing contact resistance; contact wear caused by frequent switching; and mechanical failures in the switching mechanism, preventing proper switching.
DC resistance test. Measure the DC resistance at each tap position. If the resistance at a certain position is significantly higher, it indicates poor contact at that position.
Infrared temperature measurement. During operation, use an infrared thermal imaging camera to observe the temperature distribution around the tap changer area and identify local overheating points.
Switching test. Perform step-by-step switching operations to check whether the operation is smooth and whether the tap changer reaches the correct position.
For poor contact, the transformer can first be taken out of service. The tap changer can be switched back and forth several times to remove the oxide film on the contact surface through mechanical action. If the problem remains, the active part must be lifted out for inspection. The contacts should be repaired by polishing or replaced if severely burned.
For prevention: avoid frequent operation of no-load tap changers under load conditions; regularly inspect the operating mechanism and contact condition.
Oil-immersed transformers rely on insulating oil for both insulation and heat dissipation. Once oil quality deteriorates, the transformer’s operating performance and service life will be affected.
Oil quality deterioration is indicated by: darker oil color, increased acid value, increased dielectric loss factor, and reduced breakdown voltage. The causes include oxidation of insulating oil during long-term operation. In oil-immersed transformers, insulating oil performs both insulation and cooling functions. Deteriorated oil quality reduces heat dissipation capability and lowers the overall insulation level.
Oil leakage is a very common external fault in oil-immersed transformers. Oil leakage not only reduces the oil quantity but also allows moisture and impurities to enter the oil tank, accelerating oil quality deterioration.
Oil quality analysis. Regularly collect oil samples for testing, including breakdown voltage, moisture content, acid value, and dielectric loss factor.
Oil level inspection. Check the oil level indicator. A continuous decrease in oil level indicates possible leakage.
Visual inspection. Check the oil tank, welds, valves, sealing gaskets, and other areas for signs of oil leakage.
For oil quality deterioration, filtration and regeneration treatment can be performed to remove moisture, impurities, and degradation products. Severely deteriorated oil should be replaced directly.
The treatment of oil leakage depends on the leakage location and cause: replace sealing components if the gasket is leaking; repair welds if leakage occurs at weld joints; repair or replace valves if they are leaking.
For prevention: regularly perform oil quality inspections; maintain a normal oil level and avoid excessively low oil levels; ensure the breather operates properly.
The transformer cooling system is responsible for dissipating the heat generated during operation. Once the cooling system fails, the transformer’s temperature rise may exceed the allowable limit, accelerating insulation aging.
Common cooling system faults include: blocked radiators that reduce heat dissipation efficiency; oil pump failures that interrupt oil circulation; fans not operating or running at insufficient speed; and leakage in cooler pipelines.
Oil temperature monitoring. Check the transformer’s top oil temperature. If the oil temperature is significantly higher than normal under the same load and ambient temperature conditions, it indicates that the cooling system may have a problem.
Cooling equipment inspection. Check the operating status of oil pumps and fans to confirm whether they are running properly.
Radiator inspection. Check whether the radiator surface has accumulated excessive dust, which may affect heat dissipation.
If the radiator is blocked, clean or blow it out to restore heat dissipation capacity. If the oil pump or fan is damaged, repair or replace it. If the cooler is leaking, locate and repair the leakage point.
For prevention: regularly clean radiators; regularly inspect oil pumps and fans; and conduct a comprehensive inspection and maintenance of the cooling system before the high-temperature season begins.
Fault Location | Common Fault Types | Diagnostic Methods | Treatment Measures |
|---|---|---|---|
Winding | Inter-turn short circuit, layer-to-layer short circuit, winding deformation | DC resistance test, turns ratio test, short-circuit impedance test | Repair the winding or replace damaged components |
Core | Multi-point grounding, local overheating | Grounding current detection, DGA | Eliminate abnormal grounding points |
Insulation | Aging, moisture absorption | Insulation testing, oil sample analysis | Drying treatment and restoration of insulation performance |
Tap changer | Poor contact, contact erosion, switching mechanism failure | DC resistance test, infrared temperature measurement, switching test | Remove oxide film through switching operations; polish or replace burned contacts |
Oil quality | Oil deterioration, insulating oil moisture absorption | Oil quality analysis, oil level inspection, visual inspection | Filtration and regeneration treatment; replace oil in severe cases; repair leakage points |
Cooling system | Radiator blockage, oil pump failure, fan failure | Oil temperature monitoring, cooling equipment inspection, radiator inspection | Clean radiators; repair or replace oil pumps and fans |
Preventive testing is an important method for identifying early potential faults in transformers. The main test items include:
Insulation resistance test
DC resistance test
Turns ratio test
Dielectric loss factor test
Dissolved Gas Analysis (DGA) of transformer oil
Partial discharge detection
Infrared thermal imaging detection
By regularly carrying out these tests and accumulating historical data for trend analysis, potential fault signs can be identified before they develop into serious failures.
DGA is currently one of the most widely used transformer fault diagnosis methods. When thermal faults or electrical faults occur inside a transformer, insulating oil and solid insulation materials decompose and generate specific gases. By analyzing the composition and concentration of dissolved gases in the oil, the fault type (such as overheating, discharge, insulation aging, etc.) and severity can be determined.
Different fault types produce different combinations of characteristic gases. Methods such as the three-ratio method can be used for preliminary fault identification. Regular DGA testing of important transformers and establishing gas content trend analysis can achieve early fault warning.
Infrared thermal imaging can detect the temperature distribution on the surface of equipment without shutting down the transformer and identify local overheating points. This method is suitable for detecting faults such as poor contact in tap changers, overheating of bushing connections, and local overheating of the core. It does not require shutdown or physical contact, making it relatively convenient.
With the rapid development of sensor and communication technologies, transformer online monitoring systems are becoming increasingly common. By continuously monitoring parameters such as oil temperature, winding temperature, dissolved gases in oil, and partial discharge, the operating condition of transformers can be monitored in real time.
Transformer common faults involve multiple aspects, including windings, cores, insulation, tap changers, oil quality, and cooling systems. Most faults actually show warning signs at an early stage — such as abnormal increases in oil temperature, changes in gas content, and DC resistance imbalance. If these signals can be detected and addressed in time, fault escalation can generally be avoided.
For transformer users, establishing a standardized preventive testing system, equipping necessary testing equipment, accumulating operating data, and conducting trend analysis are reliable measures to reduce fault risks and extend equipment service life.
Zisheng Electric has been engaged in the R&D and manufacturing of transformers and power equipment for many years. Its products cover oil-immersed transformers, dry-type transformers, amorphous alloy transformers, and switchgear. The company provides customized production according to standards such as IEC 60076 and GOST, serving markets in the Middle East, South America, Africa, and Russia. For inquiries regarding transformer operation and maintenance, fault diagnosis, or equipment selection, customers are welcome to send project parameters through Zisheng Electric’s official channels for technical communication.
Zisheng Electric — years of experience in power equipment R&D and manufacturing. Its products include dry-type transformers, oil-immersed transformers, amorphous alloy transformers, and switchgear, with customized production available according to international standards such as IEC 60076 and GOST. The company serves customers in the Middle East, South America, Africa, and Russia. For support related to transformer fault diagnosis, operation and maintenance, or equipment selection, please send project parameters through Zisheng Electric’s official channels to receive technical assistance.
