Oil-immersed transformers are critical for power transmission and distribution, but issues like core multipoint grounding, moisture ingress, and oil leakage can disrupt their normal operation. As a professional manufacturer and maintenance service provider, CHH Power has developed standardized solutions for these common problems, ensuring the transformer’s safety, efficiency, and long service life. Below is a detailed breakdown of CHH Power’s handling methods for core grounding issues and moisture/oil leakage faults.
1. Core Grounding Issues: Risks & CHH Power’s Resolution Methods
The iron core of an oil-immersed transformer should be single-point grounded to avoid forming current loops. Multipoint grounding (unintended additional grounding points) creates closed current circuits, leading to severe consequences: core overheating, insulating oil decomposition, silicon steel sheet deformation, and even transformer failure. CHH Power addresses this issue through two proven methods.
(1) Out-of-Box Inspection & Repair (Direct Troubleshooting)
This method is suitable for scenarios where multipoint grounding is suspected to be caused by damaged insulation or foreign objects. CHH Power’s on-site maintenance team follows these steps:
- Transformer Shutdown & Oil Drainage: Safely disconnect the transformer from the grid, drain the insulating oil (store in a clean, sealed container to avoid contamination), and remove the tank cover.
- Core Connection Point Check: Locate the core’s designated grounding point (usually a copper strip connected to the tank) and inspect for loose connections or corrosion.
- Insulation Board Paper Inspection: Examine the insulation materials between the core and the tank (e.g., insulation boards, paper gaskets) for damage, moisture, or foreign objects (e.g., metal shavings) that may cause unintended grounding.
- Repair & Replacement: Replace damaged insulation boards/paper with CHH Power’s high-temperature-resistant insulating materials (complying with IEC 60641 standards). Ensure all components are clean and properly installed to restore single-point grounding.
(2) DC Current Pulse Method (Non-Destructive Troubleshooting)
For hidden multipoint grounding (e.g., internal core insulation breakdown), CHH Power uses the DC current pulse method to eliminate redundant grounding points without disassembling the transformer:
- Equipment Connection: Connect a specialized DC pulse generator to the transformer’s core grounding terminal and the tank (ground).
- Pulse Application: Apply DC current pulses with an intensity of 4–5 times the transformer’s rated no-load current. The heating effect of the pulse current burns off weak, unintended grounding paths (e.g., tiny metal bridges or moist insulation).
- Verification: After 3–5 pulse cycles, measure the core insulation resistance using a 2500V megohmmeter. A resistance value ≥100MΩ indicates successful elimination of multipoint grounding.
- Post-Treatment: Re-inject filtered insulating oil and perform a dielectric strength test to ensure the oil meets operational standards before restarting the transformer.
2. Moisture Ingress: Causes & CHH Power’s Preventive Measures
Moisture in oil-immersed transformers degrades insulation performance, increases partial discharge, and risks short circuits. CHH Power first identifies the root causes of moisture ingress, then implements targeted solutions.
(1) Main Causes of Moisture Ingress
- Internal Leakage: Seals on the transformer’s bushings, valve covers, or flange connections degrade over time, allowing moisture to enter the tank.
- External Water Ingress: Damaged external cooling pipes, loose inspection covers, or improper storage (e.g., exposure to rain during maintenance) lead to water mixing with insulating oil.
(2) CHH Power’s Moisture Handling & Prevention
- Moisture Detection: Use a Karl Fischer moisture meter to test the water content in insulating oil (standard requirement: ≤15ppm for new oil, ≤25ppm for in-service oil). If moisture exceeds the limit, proceed with drying.
- Oil Drying Treatment:
- Circulate the insulating oil through a vacuum oil purifier (operating at ≤-0.095MPa vacuum) to remove moisture and impurities.
- For severe moisture (water content >50ppm), heat the oil to 60–70°C during vacuum treatment to accelerate moisture evaporation.
- Seal Replacement & Reinforcement:
- Replace aging seals (e.g., nitrile rubber gaskets) with CHH Power’s high-temperature, oil-resistant fluorine rubber seals.
- Apply a layer of sealant (compatible with insulating oil) to flange connections and valve covers to prevent future leakage.
3. Oil Leakage: Classification & CHH Power’s Welding Repair Techniques
Oil leakage wastes insulating oil, pollutes the environment, and reduces the transformer’s insulation performance. CHH Power classifies oil leakage by location and applies tailored welding treatments.
(1) Oil Leakage Classification & Corresponding Repairs
CHH Power’s maintenance team uses different welding methods based on the leakage area and crack type:
| Leakage Location/Type | CHH Power’s Welding Repair Method | Key Notes |
|---|---|---|
| Flat Surface Cracks (e.g., tank sidewalls) | Direct Arc Welding: Use low-hydrogen electrodes (E5015) to weld the crack directly. Preheat the area to 150–200°C to avoid cold cracks. | After welding, grind the weld to a smooth finish and perform a pressure test (0.03MPa air pressure, 30-minute hold) to confirm no leakage. |
| Cracks on Different Planes (e.g., tank corner joints) | Iron Plate Reinforcement Welding: Cut a steel plate (same material as the tank, thickness 3–5mm) to match the joint shape, place it over the crack, and weld the plate to the tank. | The plate must fully cover the crack and extend 50mm beyond the crack ends to enhance structural strength. |
| Tank Flat Area Leakage (e.g., bottom of the tank) | Continuous Welding: Clean the leakage area (remove rust, oil stains), then perform continuous welding along the leak path. | Use a welding current of 120–150A to ensure full penetration without burning through the tank. |
| Corner Cracks (e.g., tank top-angle joints) | Hole Location First: Use a magnetic particle flaw detector to locate the exact end of the crack (drill a 3–5mm hole at the end to prevent crack extension), then weld the crack. | After welding, perform a dye penetrant test to confirm no hidden cracks remain. |
(2) Post-Repair Verification
- After all welding repairs, clean the tank surface and apply anti-corrosion paint (compatible with transformer oil) to prevent rust.
- Re-inject insulating oil, perform an oil level check, and run the transformer at 70% load for 24 hours to monitor for re-leakage.
By adhering to these standardized troubleshooting and repair methods, CHH Power ensures oil-immersed transformers recover from core grounding, moisture, and oil leakage issues efficiently—minimizing downtime and extending the equipment’s service life.
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