1. Overload Operation of Distribution Transformers
Transformer overload operation occurs when the load current exceeds the transformer's rated current. Generally, when a transformer operates under light load, its insulation materials are not fully utilized; however, during sustained overload operation, the transformer generates high temperatures that cause winding insulation to harden and flake off, potentially leading to inter-turn short circuits. Simultaneously, transformer oil produces sludge that accumulates on tank walls, windings, and the core, impairing heat dissipation. This vicious cycle not only severely impacts the transformer's lifespan but can also lead to accidents such as high-voltage breakdown and transformer burnout. Therefore, three-phase load currents should be monitored regularly; they should be kept as balanced as possible, with any deviation not exceeding 10%.
2. Abnormal Sounds in Distribution Transformers
When alternating current flows through transformer windings, a normal, uniform "humming" sound is produced due to core vibration. If abnormal sounds occur, the cause must be identified, and the issue reported to the relevant department for handling. Sound characteristics differ between no-load and loaded states. The transformer should only be put into operation after the cause of any abnormal sound has been identified and compared against historical data.
3. Temperature Checks for Distribution Transformers
A transformer's operating temperature is closely linked to its lifespan. Operating at a normal temperature below 95°C yields a lifespan of 20 years; rising to 110°C shortens the lifespan to 7 years; rising to 130°C reduces it to 2 years; and continuous operation at 170°C renders the unit unusable in a very short time. If the temperature exceeds the permissible limit, the cause must be investigated and corrective measures taken promptly.
4. Checking Oil Levels and Inspecting for Seepage, Leaks, or Abnormal Oil Color
There are many reasons for a drop in oil level. Poor welding quality and inadequate sealing often lead to oil seepage or leakage at locations such as cooling tubes, valves, and tank rims. When the oil level drops below the transformer's top cover, the contact area between the oil and air increases, making the oil prone to oxidative deterioration and moisture absorption. This reduces the oil's dielectric strength, thereby compromising the insulation performance of the windings. In cases of severe oil deficiency, insulation between conductive parts and ground-or between phases-deteriorates, potentially leading to phase-to-phase or phase-to-ground breakdown and discharge. Continued operation under these conditions prevents normal oil circulation and convection, causing the oil temperature to rise, which shortens the transformer's service life or even leads to burnout .
5. Inspection of distribution transformer bushings for damage, cracks, and discharge marks
If bushings are not cleaned regularly or exhibit cracks and discharge marks, high humidity during rainy or foggy weather increases leakage current and reduces insulation performance, potentially causing flashover to ground. Furthermore, heavy accumulation of contaminants, as well as large fragments or cracks on the bushings, can lead to flashover or explosion accidents. Addressing this issue requires not only inspecting the bushings themselves but also understanding the patterns of contamination accumulation-such as the influence of wind direction and the surrounding environment-to ensure effective cleaning.
6. Periodic cleaning of distribution transformers
Dirt and contaminants on distribution transformers must be cleaned regularly. Inspections should cover the presence of flashover discharge, the integrity of the grounding connection, and the condition of leads (checking for broken wires, unsoldered joints, or fractures). Grounding resistance must be measured periodically to ensure it does not exceed 4 Ω (for capacities of 100 kVA and above) or 10 Ω (for capacities below 100 kVA); alternatively, anti-pollution measures, such as installing anti-pollution caps on bushings, should be adopted. When connecting or disconnecting transformer leads, strict adherence to operational procedures is required to prevent internal breakage of the leads.
