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Root cause investigation and Handling Solutions for Transformer Malfunctions in Humid Environments
2026-07-07
Analysis of the causes of transformer leakage and insulation deterioration in humid environments and a complete treatment plan
In scenarios such as outdoor control boxes, underground machine rooms, outdoor security equipment, coastal salt-spray environments, greenhouse sheds, underground control devices, etc., low-frequency transformers are constantly exposed to high humidity, condensation, and water vapor penetration. The most common faults are a continuous decline in insulation resistance, leakage of windings to ground, failure of withstand voltage tests, and in severe cases, creeping discharge, inter-turn breakdown, and overall machine tripping and short circuit. Many devices operate normally when there is sunlight, but they frequently experience leakage protection trips during rainy weather. Despite repeated repairs, the root cause remains elusive.
The moisture infiltration of transformer insulation is a progressive fault. Water vapor gradually seeps into the coil gaps, the core layers, the inner parts of the insulation paper and the framework. Initially, it only causes a slight decrease in insulation value. As the water vapor accumulates over time, it will gradually develop into local leakage and eventually lead to a short circuit and burnout of the coil. What are the core reasons for the deterioration of insulation caused by a humid environment? By distinguishing between surface moisture and deep water ingress, a comprehensive solution is provided, including on-site drying and dehumidification, insulation reinforcement, structural sealing, and material upgrading. This solution takes into account both the rework and rectification of finished products and the early protection of new products, aiming to solve the problem of transformer leakage in high-humidity environments from the root cause.
- The core reason for insulation degradation and leakage in humid environments
1. Water vapor penetrates into the winding interior, causing the insulation material to get wet.
Open-type transformers do not have a sealed casing. Water vapor in the air will enter the transformer through the lead-in ports, the gaps between the coils, and the gaps between the laminations of the iron core. The outer insulation paint layer of the enameled wire, the interlayer insulation paper, the frame plastic, and the insulation bushing all have hygroscopic properties. Once they absorb water vapor, the dielectric insulation strength will drop sharply. In a dry state, the insulation resistance between the winding and the ground can reach hundreds of megohms. After getting wet, it will quickly drop to several megohms or even several thousand ohms, failing to meet the safety regulations' voltage withstand requirements. Especially for products with insufficient vacuum impregnation, there are a large number of cavities inside the coil, and water vapor is trapped in the gaps. Simple baking with electricity can only dry the surface moisture, while the deep moisture cannot be discharged. Once exposed to humid weather, the failure will immediately recur.
Open-type transformers do not have a sealed casing. Water vapor in the air will enter the transformer through the lead-in ports, the gaps between the coils, and the gaps between the laminations of the iron core. The outer insulation paint layer of the enameled wire, the interlayer insulation paper, the frame plastic, and the insulation bushing all have hygroscopic properties. Once they absorb water vapor, the dielectric insulation strength will drop sharply. In a dry state, the insulation resistance between the winding and the ground can reach hundreds of megohms. After getting wet, it will quickly drop to several megohms or even several thousand ohms, failing to meet the safety regulations' voltage withstand requirements. Especially for products with insufficient vacuum impregnation, there are a large number of cavities inside the coil, and water vapor is trapped in the gaps. Simple baking with electricity can only dry the surface moisture, while the deep moisture cannot be discharged. Once exposed to humid weather, the failure will immediately recur.
2. Condensation forms liquid water droplets, causing arcing and leakage.
Outdoor equipment with large temperature differences between day and night experiences a decrease in the internal temperature at night. Water vapor in the air condenses into droplets, adhering to the coil surface, terminal connectors, and edge of the frame. These water droplets form conductive paths, creating arcing channels between high and low voltage windings and between the windings and the iron core housing, resulting in a weak leakage current. The coastal environment is also accompanied by salt fog, which dissolves in the water droplets, further enhancing their conductivity. This not only reduces insulation but also corrodes copper pins, causing copper green deposits to accumulate, continuously exacerbating the leakage problem. This is also the main reason why the insulation failure of transformers in coastal areas occurs much faster than in inland, dry regions.
3. The insulation process has inherent deficiencies and poor moisture-proofing capabilities.
Most low-priced transformers only undergo surface painting and do not undergo vacuum pressure immersion treatment. There are numerous air cavities inside the coils, making them prone to water and moisture accumulation; the insulation paper used is ordinary kraft paper, lacking moisture-proofing ability; the connection points are not sealed, allowing water vapor to penetrate easily. These transformers can be used in indoor environments for a while, but once placed in a humid outdoor environment, they will fail to meet insulation standards within just two or three months. Additionally, B-level ordinary insulation materials have poor moisture resistance. In long-term high-humidity environments, they will accelerate aging and cracking of the paint film, further exacerbating the risk of leakage.
4. The structure has no sealed design and lacks a moisture-proof barrier.
The outlet holes of the open EI type transformer are exposed, and the casing is unsealed. The entire machine has no waterproof and dustproof structure. Rainwater, fog, and condensate can freely enter and exit the transformer chamber. Even if the moisture is temporarily dried out, as long as the environmental humidity remains high, it will re-moisten within a few days, falling into a vicious cycle of "drying - moisture absorption - leakage".
- Differentiate between surface moisture and deep water ingress, and avoid ineffective repairs
Before making the rectification, it is necessary to first determine the degree of moisture absorption. The handling methods for the two situations are completely different.
The first type: surface moisture. It is only that the surface of the coil and the terminals are adsorbing moisture, and the insulation resistance fluctuates between high and low. It returns to normal on a sunny day, but leaks electricity on a rainy day. There is no water accumulation inside the winding. The treatment only requires heating and drying, and then performing surface insulation protection to repair it.
The second type: deep water ingress. Moisture seeps into the coil cavity and the interior of the insulating paper. The insulation resistance remains low for a long time. After drying, it improves temporarily, but soon deteriorates again. This situation cannot be completely eradicated by simple baking alone. It is necessary to re-impregnate with paint and seal the pores to completely seal the moisture outside the winding. Simple determination method: Let the transformer stand at room temperature for 24 hours, and measure the insulation resistance twice consecutively. If the values fluctuate greatly, it belongs to surface moisture; if the insulation remains low continuously, it can basically be determined that water has entered the interior.
- Drying and Dehumidification Process for Moist Transformers (Core Step of Repair)
1. Pre-treatment Cleaning
Remove the external rubber coating and the fixed casing of the transformer, and clean the dust, salt deposits, and copper rust on the terminals. Use isopropyl alcohol to wipe the contact posts and the outer surface of the coil, removing conductive impurities to prevent the formation of conductive dust after drying, which could create a new leakage path. For models with coastal salt spray, the salt residue must be thoroughly cleaned; otherwise, there will still be weak leakage after drying.
Remove the external rubber coating and the fixed casing of the transformer, and clean the dust, salt deposits, and copper rust on the terminals. Use isopropyl alcohol to wipe the contact posts and the outer surface of the coil, removing conductive impurities to prevent the formation of conductive dust after drying, which could create a new leakage path. For models with coastal salt spray, the salt residue must be thoroughly cleaned; otherwise, there will still be weak leakage after drying.
2. Stepped Temperature Increase Drying (Key, to prevent insulation from cracking due to sudden heating)
Do not use intense high-temperature roasting directly. Rapid temperature increase will cause the water vapor inside the coil to expand rapidly, bursting the insulation layer of the enameled wire and causing irreversible inter-turn damage.
Standard drying process:
1) Low-temperature pre-drying: 80°C for 2-3 hours, slowly evaporating surface free water vapor;
2) Medium-temperature dehydration: Increase temperature to 110°C, continuously maintaining for 6-12 hours, gradually extracting the deep moisture in the insulation paper and the gap between the coil;
3) High-temperature curing: Increase temperature to 130°C, maintaining for 3 hours, thoroughly drying the residual water vapor. After drying, cool naturally in a dry environment to room temperature immediately and measure the insulation resistance. If the insulation value returns to the qualified range, it indicates that the moisture has been completely removed; if it is still low, it means that the insulation has been broken by moisture, and there is hidden damage inside the coil, which cannot be repaired solely by drying and can only be replaced by rewinding the winding.
3. Vacuum Impregnation and Reinforcement, Sealing Capillary Pores
After reaching the drying standard, to prevent re-moisture absorption, a second vacuum impregnation must be carried out. The insulating paint fully penetrates every tiny gap of the coil in a vacuum environment, solidifying to form a dense waterproof sealing layer, completely isolating water vapor from invading again. For batch repair products, moisture-resistant epoxy insulating paint should be preferred; for small batch repair parts, two coats of insulating clear paint can be applied on the outer surface of the coil to seal the exposed gaps. The root of the leads and the terminal positions should be thickly coated to prevent water vapor from penetrating inward through the outlet.
- Long-term Moisture Prevention Solution: Structural Sealing Modification, Blocking the Water Vapor Entry Path
Drying and dehumidification can only solve the current moisture-related problems. To achieve stable operation in a humid environment for a long time, it is necessary to ensure the complete sealing of the entire machine and build multiple layers of moisture-proof barriers.
1. Sealing Treatment of Lead-out Ports: The transformer lead-out holes are completely sealed with epoxy glue and silicone sealant, leaving no gaps, to prevent fog and condensation from entering the coil through the gaps in the wires. The outlet ports of multiple leads are fully encapsulated, without leaving any air vents.
2. Whole Machine Encapsulation and Bonding Treatment: In high-humidity, outdoor, and salt spray environments, an open structure is abandoned and epoxy resin is used for overall encapsulation. The iron core and coil are sealed together in the rubber body, preventing water vapor from contacting the winding. The insulation resistance can be maintained stably for a long time, completely eliminating leakage. Encapsulation is the most cost-effective renovation solution for outdoor humid conditions and is widely used in outdoor security power supplies and underwater control transformers.
3. Installing an Enclosure and Doing Box Moisture Prevention: If the transformer is installed in an electrical control box, the box should have a waterproof sealing ring, and a drainage hole should be reserved at the bottom to avoid water accumulation. Dryers and dehumidification modules should be added inside the box to control the humidity inside the cavity. At the same time, avoid the transformer being in close contact with the metal base plate and install an insulating base to prevent condensation from directly soaking the bottom of the transformer.
4. Reasonably Avoiding Temperature Difference Condensation: Avoid excessive temperature differences between day and night. If conditions permit, a small heater should be installed to keep the box temperature above the dew point, preventing condensation water droplets from forming at the source. Many outdoor equipment leaks are not caused by rainwater infiltration, but by night-time condensation.
- Upgrading materials for new products in the early stage, enhancing insulation performance against moisture from the source
If it is a custom transformer for a new project, optimize the materials and processes in advance to significantly improve the moisture resistance level, avoiding repeated rectification later. First, upgrade the insulation materials. Select F-class and H-class moisture-resistant insulation materials, and replace ordinary kraft paper with polyester film insulation paper, which has significantly improved water resistance and anti-humidification capabilities; the enameled wire uses direct welding polyurethane moisture-resistant enameled wire, with a dense paint film that is not easily eroded by water vapor. Second, adopt the forced vacuum pressure immersion coating process. Reject ordinary brushing, and conduct overall vacuum immersion coating of the coils, allowing the insulating paint to fill all the winding gaps, solidifying the entire coil into a solid structure, cutting off the water vapor penetration path. Third, increase the creepage distance of the windings. According to safety standards, widen the initial and secondary winding spacing, increase the insulation isolation between the windings and the iron core, preventing cross-layer creepage leakage in humid environments. Fourth, categorize product selection based on different conditions: for ordinary indoor humid environments, droplet immersion treatment can be performed; for open-air, seaside salt fog environments, directly adopt the full epoxy encapsulation structure; for underground, high condensation scenarios, additional three-proof coatings (moisture-proof, mold-proof, salt fog-proof) are added.
- Daily Insulation Testing and Preventive Maintenance
In a humid environment, the insulation of transformers will gradually deteriorate. Regular testing can help predict faults in advance. Every month, use an ohmmeter to measure the insulation resistance between the windings and ground, as well as between the primary and secondary sides. The normal insulation resistance of a dry transformer should be greater than 100 MΩ; if it is lower than 10 MΩ, it indicates slight moisture absorption and timely drying maintenance should be arranged; if it is lower than 1 MΩ, insulation damage has occurred and the equipment must be shut down for maintenance. Before the rainy season arrives, conduct a comprehensive dehumidification and drying of outdoor equipment in advance, clean the oxide layer on the terminals, apply insulating sealant, and eliminate potential hazards at the initial stage. Do not wait until an electrical leakage trip occurs and then carry out emergency repairs; reduce equipment downtime losses.
In a humid environment, transformers may experience leakage and a decline in insulation. The apparent cause is moisture absorption, but the root cause can be divided into two layers: short-term faults are caused by water vapor entering the coils, resulting in a decrease in insulation; long-term recurrence is due to the lack of sealing in the process, the absence of waterproof structure, and insufficient moisture resistance of the materials. The handling process must be carried out in two steps: first, through stepwise drying to remove the internal moisture, and then repair the current leakage fault; second, through dip coating sealing, sealing filling, and blocking the water vapor from penetrating again through the box body's moisture-proof measures. Simply relying on electrical drying can only provide temporary relief; only by completely sealing the winding pores, ensuring the entire machine has waterproof isolation, and combining with high moisture-resistant insulation materials, can the problem of insulation decline during rainy weather and frequent tripping be truly solved. Whether it is after-sales repair and rectification or new product development, implementing the three-in-one solution of "moisture removal + sealing + material upgrade" is necessary to ensure that transformers can operate stably for a long time in high humidity, condensation, and salt spray environments, and to prevent leakage breakdown accidents.
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