Distribution transformers frequently face overheating issues during their daily operations. Prolonged overheating can lead to severe damage, potentially causing the transformer to burn out and jeopardizing the entire power supply system. To prevent such failures, it is crucial to identify the root causes of overheating and address existing problems promptly, thereby reducing the risk of further damage and ensuring the safe and stable operation of the power grid.
I. Analysis of Overheating Causes in Distribution Transformers
Overheating in distribution transformers is not a normal part of operation. Under normal conditions, the temperature rise comes from the windings and core. However, overheating faults typically originate from hot spots within the solid insulation, which can lead to insulation degradation and even pyrolysis. These hot spots often develop gradually, starting at lower temperatures and escalating over time—sometimes rapidly turning into arcs that cause catastrophic failure. The nature and location of these hot spots vary, and so do the underlying causes.
Common causes of overheating in distribution transformers include:
1. Winding Overheating: After years of operation, the insulation may expand, blocking oil channels between winding sections. This poor oil flow reduces cooling efficiency, and prolonged electromagnetic vibration can cause the insulation to degrade and fall off, leading to short circuits between turns or layers, ultimately resulting in transformer failure.
2. Tap-Changer Issues: Long-term use of the tap-changer can result in mechanical wear, electro-corrosion, and contact contamination, leading to poor contact and overheating at the joints.
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 heat buildup.
4. Transformer Leads: Loose connections, broken leads, or improperly secured conductive rods can all contribute to overheating at the connection points.
5. Foreign Objects Inside the Transformer: During maintenance or assembly, foreign materials may remain inside, causing short circuits or local overheating due to induced currents.
6. Cooling System Failures: Damage to cooling components, clogged silica gel, silt blockages, or oil flow restrictions can all impair the cooling system, leading to overheating.
II. Mitigation Measures
Each overheating issue requires specific handling based on its cause. Here are some effective measures:
1. For internal component-related overheating, inspect the transformer’s interior for signs of overheating, increase insulation clearance, ensure unobstructed oil flow, repair exposed wires, check for foreign objects inside the tank, confirm proper grounding, and maintain appropriate distances between internal parts and the casing. Filtering the transformer oil to improve dielectric strength is also essential.
2. When dealing with lead wires or tap-changers, ensure proper connections and tighten all fastening screws securely to prevent overheating caused by loose contacts.
3. For magnetic leakage-related overheating, locate and fix the leakage points (such as worn rods or misaligned components), reinforce and insulate all core parts, and install magnetic shields inside the transformer tank to guide the leakage flux through the shield rather than the tank walls, thus avoiding excessive losses and local overheating.
4. If the cooling system is faulty or blocked, replace damaged fans and regularly clean the cooling tubes using compressed air or water to restore efficient cooling.
5. Strengthen daily inspections and monitoring. Check the color change of silica gel, monitor oil levels, and top up if necessary. Use the "look, smell, ask, cut" method or instrument testing to assess the transformer’s condition, perform preventive tests, and make a comprehensive judgment about its operational status.
By implementing these strategies, utility companies can significantly reduce the risk of transformer failures, ensuring reliable power delivery and minimizing downtime.
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