Dry-type transformer fault monitoring: fault types, cause analysis and monitoring system

Date: November 3, 2025 08:09:26

Dry-type transformers are widely used in high-rise buildings, data centers, subways and other places with high safety requirements due to the advantages of oil-free, fire and explosion-proof, and convenient maintenance. However, its operation is affected by the environment, load, manufacturing process and other factors, prone to various types of faults, accurate identification of fault types, clear causes and build an efficient monitoring system is essential to ensure the stable operation of the power system.

First, dry-type transformer common types of failure

Failures of dry-type transformers are mainly concentrated in the core components and operating systems, and common types include the following categories:
  1. Winding Failure: The most common and hazardous faults include winding overheating, turn-to-turn short circuits, phase-to-phase short circuits, and winding deformation.
  2. Core failure: Mainly manifested as iron core multi-point grounding, iron core loss is too large, iron core loose or vibration abnormality.
  3. Insulation failure: Dry-type transformers are mostly epoxy casting or non-encapsulated insulation, failure forms of insulation aging, insulation moisture, insulation damage discharge.
  4. partial discharge fault: Localized electric field concentration within or on the surface of the insulation triggers local breakdown discharges, which are an important precursor to insulation degradation.
  5. Cooling system failure: For forced air-cooled (AF) dry-type transformers, it is common for fans to be damaged, air speed to be insufficient, and cooling channels to be blocked.

II. Core causes of failure

Dry-type transformer failure is not caused by a single factor, but the design, manufacture, operation, environment and other factors play a joint role in the results:

1. Design and manufacturing defects

  • The winding process is not up to standard, resulting in uneven wire arrangement and insufficient thickness of the insulation layer, which buries the potential danger of turn-to-turn short circuit.
  • Insufficient precision of iron core stacking, insufficient clamping force, vibration and excessive eddy current loss in operation, triggering iron core overheating.
  • Improper selection of insulation materials, temperature resistance level or mechanical strength does not meet the requirements of the working conditions, easy to aging damage.

2. Abnormal operating conditions

  • Long-term overload operation, the winding loss increases significantly, the temperature exceeds the insulation tolerance limit, accelerating insulation aging and winding deformation.
  • Voltage fluctuation is too large or three-phase load imbalance, resulting in iron core magnetic density saturation, loss increase and vibration noise.
  • Frequent start-stop or sudden short-circuit impact, the winding is subjected to huge electromagnetic force, which is easy to cause wire deformation and loose joints.

3. Impact of environmental factors

  • Environmental humidity exceeds the standard, and the insulating material of the non-sealed dry-type transformer absorbs moisture, leading to a drop in insulation resistance and triggering discharge faults.
  • Dust, corrosive gases (such as chemical plants, coastal areas) attached to the winding or core surface, damage to the insulation layer and accelerate the corrosion of components.
  • The ambient temperature is too high, exceeding the cooling system's ability to dissipate heat, resulting in an abnormal overall temperature rise of the equipment.

4. Lack of maintenance management

  • Failure to regularly clean the heat dissipation channel, dust accumulation leads to poor ventilation, reduced cooling efficiency triggers overheating.
  • Preventive tests such as insulation resistance testing and partial discharge detection have not been carried out for a long time, and potential faults cannot be detected in time.
  • Cooling system fans, sensors and other components are not regularly serviced and are not replaced in a timely manner after failure.

Third, dry-type transformer fault monitoring system classification and features

Dry-type transformer fault monitoring system is divided into traditional preventive monitoring and online real-time monitoring of two categories, both complement each other to form a complete monitoring system:

1. Traditional preventive monitoring systems

Periodic manual inspection is the main focus, suitable for scenarios with low failure rates and simple working conditions, and the core approach includes:
  • Insulation resistance test: Measure the insulation resistance of the windings to ground and between phases by shaking table to determine the degree of moisture or aging of the insulation.
  • DC Resistance Test: Detect the DC resistance value of the winding, and troubleshoot problems such as loose winding joints and turn-to-turn short circuits.
  • Partial Discharge Detection: Use ultrasonic detectors or portable partial discharge testers to detect discharge signals on site on a regular basis.
  • infrared thermometry: Scanning the surface of a transformer with an infrared camera to identify areas of overheating in windings, cores, joints, etc.

2. Online real-time monitoring system

Based on sensor technology and data transmission technology, it realizes 24 hours uninterrupted monitoring, suitable for important load places, the core module includes:
  • Temperature monitoring moduleThe temperature of the winding, core and environment is collected in real time by fiber optic temperature sensor or PT100 sensor, and the alarm is automatically generated when the temperature exceeds the limit.
  • Partial Discharge On-Line Monitoring Module: The discharge signal is collected through the built-in coupling sensor, combined with the algorithm to analyze the discharge intensity and location, and warn of insulation failure in advance.
  • Vibration Monitoring Module: Collecting transformer operation vibration signals through vibration sensors to analyze the characteristics of faults such as iron core loosening and winding deformation.
  • Integrated monitoring platform: Integrate all kinds of monitoring data, realize remote monitoring, data storage, fault diagnosis and historical data analysis, and improve the efficiency of operation and maintenance.

Fourth, what are the common problems of fault monitoring of dry-type transformers

  1. Q: What are the common signs of overheating in dry-type transformer windings?A: The main manifestations are abnormal increase in the surface temperature of the equipment, continuous high-speed operation of the cooling fan, odor (insulation aging), the load factor does not exceed the standard but the temperature rise exceeds the standard.
  2. Q: How much does ambient humidity affect dry-type transformer insulation?A: the impact is significant, the relative humidity exceeds 85%, non-encapsulated transformer insulation material is easy to absorb moisture, resulting in decreased insulation resistance, and even triggered partial discharge, it is recommended to control the operating environment humidity in 40%-70%.
  3. Q: What are the advantages of an online monitoring system over traditional manual monitoring?A: Advantages include strong real-time, 24-hour uninterrupted monitoring; the ability to capture transient fault signals (such as sudden partial discharge); reduce the cost of manual inspection; and the realization of remote warning to avoid the expansion of the fault.
  4. Q: Do partial discharges in dry-type transformers necessarily mean insulation failure?A: Not necessarily, slight partial discharge may be caused by temporary environmental factors (such as excessive humidity), but if the discharge intensity continues to rise or occurs frequently, it indicates that the insulation has deteriorated and needs to be dealt with in a timely manner.
  5. Q: What can happen when a forced air-cooled dry-type transformer fan fails?A: Fan failure will lead to a sudden drop in cooling efficiency, if the transformer is running under load, the winding temperature will rise rapidly, which may trigger accelerated aging of the insulation in the short term, and may lead to a short-circuit in the winding in the long term.
  6. Q: How to determine whether there is a multi-point ground fault in the core of a dry-type transformer?A: can be measured by the core to ground insulation resistance, if the resistance value is lower than 1MΩ, the probability of multi-point grounding; at the same time combined with vibration monitoring, multi-point grounding will lead to abnormal vibration of the core, loss increase.
  7. Q: What is the main cause of winding deformation in dry-type transformers?A: The main reasons include sudden short-circuit shock, long-term overload operation, impact during transportation or installation, and insufficient clamping force during winding.
  8. Q: Do the sensors in an online monitoring system require regular maintenance?A: Yes, it is recommended to check the sensor wiring for loose wires, fiber optic sensor for breakage, and temperature sensor calibration accuracy every 6-12 months to ensure accurate monitoring data.
  9. Q: Can dry-type transformers be operated in dusty environments?A: It is not recommended to run for a long time, dust accumulation will block the heat dissipation channel, resulting in poor heat dissipation, while dust may contain conductive impurities, attached to the insulation surface will reduce the insulation performance, need to be regularly cleaned up and good dust control measures.
  10. Q: What is the relationship between preventive testing and online monitoring?A: The two are complementary, online monitoring focuses on real-time early warning, preventive testing (such as annual insulation test, DC resistance test) focuses on in-depth investigation of potential faults, the combination of the use of transformers can be comprehensive to ensure safe operation.