1. Overload Operation of Distribution Transformers
Transformer overload operation refers to the load current exceeding the rated current of the transformer. Generally, when a transformer is operating at low load, its insulation material cannot fully function. However, during continuous overload operation, the transformer generates high temperatures, causing the winding insulation to burn and fall off, resulting in inter-turn short circuits. Furthermore, transformer oil forms sludge, which accumulates on the oil tank plate, windings, and core, impairing heat dissipation.
2. Abnormal Sounds from Distribution Transformers
When AC current passes through the transformer windings, a normal, uniform "humming" sound is produced due to the core's self-vibration. If an abnormal sound occurs, the cause must be identified and promptly reported to the relevant authorities for action. Transformers also sound differently when unloaded and loaded. Compare the characteristics of the abnormal sound with previous sounds to determine the cause before resuming operation.
3. Temperature Inspection of Distribution Transformers
The operating temperature of a transformer has a significant impact on its lifespan. A transformer operating at a normal temperature below 95°C has a lifespan of 20 years. If it rises to 110°C, its lifespan is shortened to 7 years; if it rises to 130°C, its lifespan is reduced to 2 years; and if the temperature rises to 170°C, the transformer will fail in about 2 days. If the temperature exceeds the transformer's allowable limit, the cause must be identified and corrective measures implemented promptly.
4. Check the oil level in the distribution transformer for any seepage, leakage, or abnormal oil color.
There are many reasons for a low oil level. Poor welding and sealing can lead to oil seepage and leakage in heat pipes, valves, and casing edges. When the oil level drops below the transformer's upper cover, the oil's contact surface with the air increases, making it susceptible to oxidation and deterioration, as well as absorption of moisture from the air. This reduces the oil's compressive strength, thereby damaging the winding's insulation. Severe oil deficiency reduces the insulation between the transformer's conductive parts and the ground, as well as between each other, causing phase-to-phase or phase-to-ground breakdown discharges. If the transformer continues to be used at this point, the transformer oil will not circulate properly, causing the transformer oil temperature to rise, shortening its lifespan, or even burning out.
5. Check the distribution transformer's insulating bushing for damage, cracks, or signs of discharge.
If the insulating bushing is not cleaned for a long time or has signs of damage, cracks, or discharge, the leakage current of the bushing will increase due to humidity in rainy or foggy weather, reducing insulation and causing flashover to ground. Additionally, severe fouling, large debris, or cracks on the bushing can also cause flashover or explosion. To address this issue, in addition to inspecting the bushing itself, it's also important to pay attention to the pattern of contamination, such as wind direction and surrounding conditions, to ensure proper cleaning.
6. Regular Cleaning of Distribution Transformers
Clean dirt from distribution transformers regularly. Check bushings for flashover discharges, ensure proper grounding, and check for broken wires, desoldering, or fractures. Regularly measure ground resistance, ensuring it is no greater than 4 Ω (for capacity 100 kV·A and above) or 10 Ω (for capacity less than 100 kV·A). Alternatively, implement anti-fouling measures such as installing bushing anti-fouling caps. When connecting and disconnecting distribution transformer leads, strictly follow procedures to avoid internal fractures.