The term "distribution transformer," often abbreviated as "distribution," refers to a static electrical device that transfers AC energy based on the principle of electromagnetic induction, enabling the conversion of AC voltage and current levels. In certain regions, power transformers with voltage levels below 35 kV (primarily 10 kV and below) are termed "distribution transformers" and commonly referred to simply as "distributions." These transformers are typically installed either on utility poles or on open floors within substations. Detailed explanations regarding their installation methods, safety precautions, power supply distribution approaches, capacity selection, operational procedures, and routine maintenance are available.
So, what are the key aspects of maintaining distribution transformers?
Firstly, overloading a distribution transformer is a major concern. This occurs when the load current exceeds the transformer's rated capacity. Normally, when a transformer operates under light loads, its insulation materials aren't fully utilized. In cases of prolonged overloading, excessive temperatures can develop, damaging the insulation of the windings and leading to turn-to-turn short circuits. Additionally, sludge may accumulate on the tank walls, windings, and cores, hampering the transformer oil’s ability to dissipate heat. This creates a harmful cycle that significantly reduces the transformer's lifespan, potentially resulting in high-voltage breakdowns and transformer failures. Therefore, it's crucial to monitor the three-phase load currents regularly. Ideally, the currents should be balanced, with any deviations kept within 10%.
Secondly, abnormal sounds from the transformer warrant attention. Under normal conditions, the transformer produces a consistent humming noise due to the vibration of the iron core when AC power flows through the windings. However, unusual noises could indicate underlying issues. Depending on whether the transformer is idle or loaded, the sound characteristics change. Once the root cause of the abnormal sound is identified, appropriate action can be taken before putting it back into service.
Thirdly, monitoring the transformer's temperature is essential. Transformer lifespan is closely tied to its operating temperature. Operating at 95°C provides a lifespan of about 20 years, whereas temperatures rising to 110°C reduce this to 7 years, and reaching 130°C cuts it further to just 2 years. Continuous operation at 170°C will render the transformer unusable. If the temperature exceeds acceptable limits, it's imperative to investigate the cause and implement corrective measures promptly.
Fourthly, checking the transformer's oil level is vital. Oil leakage due to poor welding, sealing, or damaged heat pipes, valves, or box edges can lower the oil level. When the oil level drops below the tank cover, increased contact with air leads to oxidation, degradation, and absorption of moisture, reducing the oil's dielectric strength and compromising insulation. Severe oil shortages can decrease insulation between conductive parts and ground, increasing the risk of phase-to-phase or ground faults. Continued use under these conditions risks disrupting normal oil circulation, causing overheating, shortening the transformer's life, and potentially leading to catastrophic failure.
Fifthly, inspecting the insulation bushings for damage, cracks, or discharge marks is important. Neglecting bushing cleanliness or allowing damage can result in increased leakage current during humid conditions, reducing insulation effectiveness and leading to ground flashovers. Heavy contamination can cause flashovers or explosions. Addressing this requires not only cleaning the bushings but also understanding environmental factors like wind direction and surrounding pollution sources to ensure proper maintenance.
Lastly, regular cleaning of the transformer is recommended. Dirt accumulation should be removed, along with checking for flashover discharges, grounding integrity, and ensuring connections remain secure. Grounding resistance should be measured periodically, ensuring it doesn’t exceed 4 ohms for capacities above 100 kVA or 10 ohms for smaller units. Anti-pollution measures and caps might also be installed. When handling lead wires, follow proper procedures to prevent internal breaks.
In conclusion, maintaining a distribution transformer involves careful monitoring of its operational parameters, regular inspections, and prompt corrective actions to ensure longevity and safe operation.
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