Oil-immersed transformer failures are mainly driven by eight key factors, with line inflow (disturbance) as the primary cause, followed by insulation degradation, insufficient maintenance, and overload. Most failures are avoidable through standardized operation, enhanced maintenance, and quality control—effectively extending the transformer’s service life from the current average 17.8 years to the expected 35–40 years. Below is a detailed breakdown of each failure cause and CHH Power’s targeted solutions.
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1. Primary Failure Cause: Line Inflow (Line Disturbance)
This is the most critical factor leading to transformer failures, encompassing power distribution anomalies and voltage disturbances:
- Key Manifestations:
- Operational errors (e.g., incorrect transformer pairing, misoperation of switches).
- Tap switch lead arcing, resulting in overvoltage, peak voltage surges.
- Line faults (e.g., flashovers) and incorrect phase matching.
- Impact: Directly causes insulation breakdown, winding damage, or core overheating, leading to sudden transformer failure.
2. Secondary Failure Cause: Insulation Degradation
Insulation deterioration is the second leading failure factor, severely shortening the transformer’s service life:
- Key Manifestations:
- Aging of insulating oil, insulating paper, and insulating boards due to long-term operation, temperature fluctuations, or moisture ingress.
- Impact: Reduces the transformer’s average service life to 17.8 years—far below the expected 35–40 years. For transformers failing in 1983, the average life was 20 years, indicating a downward trend in durability.
3. Third Failure Cause: Overload
Overload refers to long-term operation exceeding the nameplate power, common in grids with gradually increasing loads:
- Key Manifestations:
- Small-capacity transformers carrying excessive loads for extended periods (e.g., power stations or power companies with unplanned load growth).
- Impact: Causes excessive temperature rise, accelerating insulation aging. Deteriorated insulation boards and reduced insulating paper strength lead to insulation breakdown when exposed to external faults, triggering failures.
4. Fourth Failure Cause: Insufficient Maintenance
Inadequate maintenance ranks fourth, covering neglect of protective measures and equipment upkeep:
- Key Manifestations:
- Illegal modification or improper use of protection devices.
- Lack of necessary monitoring equipment for transformers.
- Coolant leakage, excessive dirt accumulation, and corrosion of components.
- Impact: Turns minor defects into major failures (e.g., unaddressed coolant leakage leads to overheating; corrosion damages core and windings).
5. Other Failure Causes
(1) Three-Phase Load Imbalance
- Manifestation: Long-term unbalanced three-phase loads lead to partial overload and excessive temperature rise.
- Impact: Deteriorates insulation, causing inter-coil or inter-phase short circuits.
(2) Loose Connections
- Manifestation: Improper tightening of bolted connections, inappropriate use of dissimilar metals (leading to electrochemical corrosion), and loose electrical connections (during manufacturing or maintenance).
- Impact: Causes local arcing, overheating, or poor contact—though the phenomenon has decreased in recent years.
(3) Poor Process/Manufacturing Defects
- Manifestation: A small proportion of failures stem from manufacturing flaws, such as loose sockets, missing supports, loose cushions, poor welding, inadequate core insulation, insufficient short-circuit strength, or foreign objects in the tank.
- Impact: Hidden defects that trigger failures under harsh conditions (e.g., overload, short circuit).
(4) Lightning Strikes
- Manifestation: Fewer direct lightning strike failures than in previous studies; non-obvious lightning impacts are now classified as line inflow (inrush current).
- Impact: Induces overvoltage, damaging insulation and windings.
6. CHH Power’s Targeted Countermeasures
To mitigate these failures, CHH Power recommends a combination of preventive measures and technical optimizations:
- Strengthen Line Disturbance Control:
- Install surge arresters and overvoltage protection devices to suppress peak voltages and inrush currents.
- Standardize operational procedures (e.g., strict switch operation protocols, phase-matching checks before transformer pairing).
- Insulation Condition Monitoring:
- Conduct regular insulation tests (e.g., dielectric strength test for oil, insulation resistance test for windings) and oil chromatographic analysis to detect degradation early.
- Replace aging insulating materials (e.g., insulating paper, boards) periodically, using high-temperature, moisture-resistant materials.
- Standardize Maintenance Practices:
- Establish a regular maintenance schedule (quarterly for coolant leakage checks, semi-annually for dirt cleaning and corrosion inspection).
- Ensure protection devices are correctly configured and functional; install real-time monitoring systems (e.g., temperature, oil level sensors).
- Load Management:
- Monitor load capacity in real time; avoid long-term overload by expanding capacity or adding transformers for growing loads.
- Balance three-phase loads to prevent partial overload, using intelligent load distribution systems.
- Connection Quality Control:
- Use compatible metals for connections; tighten bolts to specified torque during manufacturing and maintenance.
- Conduct regular contact resistance tests to detect loose connections early.
- Manufacturing Process Optimization:
- Implement strict quality inspections (e.g., welding quality checks, core insulation tests) to eliminate defects before delivery.
- Remove foreign objects from the tank and ensure secure installation of supports and cushions.
- Lightning Protection Enhancement:
- Upgrade lightning arresters for transformers in lightning-prone areas; optimize grounding systems to reduce induced overvoltage.
By addressing these failure causes proactively, oil-immersed transformers can operate safely and reliably, approaching their designed service life.
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