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Time：2025-08-22 13:25:16 Reading volume：
Okay, this is a very important and professional power equipment maintenance issue. Water in the insulating oil must be promptly and properly addressed; otherwise, it poses a serious threat to the safe operation of power equipment (such as transformers and instrument transformers).
Treating water in the insulating oil is not a single operation, but a systematic process. The diagram below clearly illustrates the entire process from discovery to resolution:
Below are detailed instructions and precautions for each step:
1. Shut down the equipment (depending on the severity of the situation):
If online monitoring reveals a trace increase in moisture, and electrical test data (such as withstand voltage test and dielectric loss factor) has not significantly deteriorated, strengthen monitoring and arrange for dehydration as soon as possible.
If the moisture content is high, or the oil withstand voltage drops sharply, or if water accumulation is detected within the equipment, shut down the equipment immediately to prevent further damage. Moisture reduces the dielectric strength of the oil, potentially causing internal short circuits or arcing.
2. Isolation and Diagnosis:
Isolate the equipment from the power grid and implement safety measures. Take samples for a comprehensive oil analysis, including moisture content, breakdown voltage, and dielectric loss factor (tan δ), to accurately assess the extent of oil deterioration.
At the same time, make every effort to identify the cause of water ingress. Otherwise, even after oil treatment, the problem will recur.
This is the key to fundamentally resolving the problem. Common causes of water ingress include:
Breathing system failure: The silicone inside the breathing device is deteriorating or not replaced promptly, allowing moisture to enter the oil conservator through the breathing device.
Sealing system failure: Poor seals in equipment flanges, valves, welds, and casing tips allow water or moisture to enter.
Cooling system leaks: Cooler pipes in water-cooled equipment rupture, allowing water to seep into the oil.
During installation or maintenance: During operations such as lifting covers and replacing windings, the device body is exposed to humid air, resulting in incomplete drying or improper seal restoration.
Condensation due to temperature differences: Rapid fluctuations in oil temperature can cause condensation to form within the equipment.
Depending on the degree of water ingress and equipment conditions, ｓｅｌｅｃｔ one or more of the following methods in combination:
1. Vacuum Hot Oil Circulation (the most common and effective method)
Principle: The oil is heated to a certain temperature (usually 50-60°C). A vacuum is then applied in a vacuum tank to lower the boiling point, causing the dissolved and emulsified water in the oil to rapidly vaporize and be removed.
Methods:
Offline Treatment: All oil in the equipment is extracted and injected into a dedicated vacuum oil filter for dehydration. Once qualified, it is returned to the equipment.
Online Treatment: The vacuum oil filter is connected to equipment such as a transformer and dehydrated without shutting down the equipment. This method is suitable for mild water ingress and does not require equipment downtime.
2. Centrifugal Separation
Principle: The difference in density between oil and water creates a strong centrifugal force in a high-speed centrifuge, separating water from the oil.
Features: Primarily used to separate free water (i.e., suspended water droplets visible to the naked eye), it is only marginally effective in removing dissolved water. This is usually used for preliminary dehydration or pretreatment.
3. Adsorption Method
Principle: Oil is passed through a filter filled with a high-efficiency adsorbent (such as silica gel or molecular sieve). The adsorbent removes moisture from the oil by adsorption.
Features: It effectively reduces trace moisture, but the adsorbent easily saturates and requires frequent replacement. It is often used as a deep purification method after vacuum dehydration.
For oil that has been severely waterlogged or severely deteriorated, it may be necessary to completely ｒｅｐｌａｃｅ the oil. However, before replacing the new oil, the internal moisture and water content of the equipment must be thoroughly removed to prevent re-contamination after the new oil is injected.
4. Drying the Equipment Internals
If water has entered the insulating oil, it means that the internal components of the equipment (solid insulation materials, windings, core, etc.) are likely also damp. Simply treating the oil is not enough; the internal components of the equipment must be dried. Common methods include:
Hot Oil Flushing: Dry, high-temperature hot oil is circulated throughout the equipment to remove moisture from the insulation materials. The oil is then passed through an oil filter to remove the moisture. Vacuum Drying: The equipment body is subjected to a high vacuum, supplemented by circulating heated nitrogen or hot oil to efficiently evaporate internal moisture under vacuum.
After oil treatment, sampling and testing must be conducted in strict accordance with standards (such as GB/T 7595 "Quality of Transformer Oil in Operation") to ensure compliance with the following key indicators:
Water Content: 330 kV and above equipment: ≤10 mg/L; 220 kV and below equipment: ≤15/25 mg/L (standards vary slightly).
Breakdown Voltage: Depending on the voltage level, typically ≥40-60 kV is required.
Dielectric Dissipation Factor (90°C): Typically ≤0.5% or 0.7%.
Only after all indicators pass must the equipment be re-commissioned. Oil quality monitoring should be strengthened during the initial period of operation.
In summary, the principles for handling water ingress into insulating oil are: immediate assessment, identification of the cause, coordinated treatment of the oil and equipment, and rigorous acceptance inspection.
