Distribution transformers often face overheating issues during normal operation, which can lead to serious failures if not addressed promptly. Prolonged overheating may result in transformer burnout, posing a direct threat to the stability and safety of the power supply system. Therefore, it is crucial to identify the root causes of overheating and take immediate corrective actions to minimize failure risks and prevent further damage.
**I. Analysis of Overheating Causes in Distribution Transformers**
Overheating in distribution transformers is different from normal temperature rise, which primarily comes from winding and core losses. However, overheating faults typically occur due to localized hotspots within the solid insulation, leading to insulation degradation or even pyrolysis. These hotspots often develop gradually from low temperatures to high temperatures, and in severe cases, they may lead to arcing, ultimately causing transformer failure. The causes of these hotspots vary depending on the specific conditions inside the transformer.
Common causes of overheating include:
1. **Winding Overheating**: After years of operation, the insulation materials in the windings may expand, blocking oil channels between winding layers. This reduces oil flow and weakens cooling effectiveness. Long-term electromagnetic vibrations can cause insulation to age and break off, leading to inter-turn or segment short circuits and eventual burning of the transformer.
2. **Tap-Changer Issues**: The tap-changer may suffer mechanical wear, electro-corrosion, or contamination over time, resulting in poor contact and loose connections that generate excessive heat.
3. **Magnetic Circuit Faults**: Magnetic flux leakage from the silicon steel sheets can cause localized overheating. Additionally, iron core clamps or foreign objects may create short circuits or multiple grounding points, leading to circulating currents and overheating.
4. **Transformer Leads**: Damaged or poorly connected leads, as well as loose conductive rods, can cause overheating at connection points.
5. **Foreign Objects Inside**: During maintenance or assembly, foreign materials left inside the transformer can cause winding short circuits or local overheating due to current circulation.
6. **Cooling System Failures**: Damage to cooling components such as fans, silica gel blockage, silt accumulation, or oil clogging can all contribute to overheating.
**II. Measures for Handling Overheating Issues**
The treatment methods depend on the specific cause of the overheating:
1. **Internal Component Issues**: If overheating is caused by internal components like windings, it's necessary to inspect the transformer’s interior, increase insulation spacing, ensure unobstructed oil flow, repair exposed wires, check for foreign objects, and maintain proper clearance between the core and the tank. Filtering the transformer oil can also improve its dielectric strength.
2. **Lead and Tap-Changer Connections**: Ensure proper connections for leads and tap-changers, and tighten all fastening screws with double caps to prevent loosening and subsequent heating.
3. **Magnetic Leakage Problems**: Identify and address leakage points (e.g., worn rods touching the tank), reinforce core insulation, and install magnetic shields inside the tank to guide the leakage flux through the shield instead of the tank walls, reducing local overheating.
4. **Cooling System Maintenance**: Replace damaged fans and regularly clean the cooling tubes using compressed air or water to prevent blockages.
5. **Routine Monitoring and Inspection**: Enhance daily inspections by monitoring the discoloration of silica gel, oil level changes, and promptly refilling oil when needed. Use the “look, smell, ask, cut†method or instrument testing to assess the transformer’s condition and perform preventive tests for comprehensive evaluation.
By implementing these measures, the risk of overheating-related failures can be significantly reduced, ensuring the long-term reliability and safety of distribution transformers.
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