Analysis Of Common Faults Of Distribution Transformers

1. Three-phase load imbalance or seasonal overload
According to the survey results, there is a large number of three-phase load imbalances in distribution transformers. Especially in rural areas, most of the power loads are single-phase loads, and the loads vary greatly. Therefore, there are many distribution transformers with three-phase load imbalances. The three phases cannot operate symmetrically, resulting in zero sequence current. On the one hand, this increases the loss of the transformer, and on the other hand, it reduces the effective capacity of the transformer. The above two situations will cause the transformer to overheat, the insulating oil to age, and the winding insulation level to decrease, which will eventually lead to damage to the transformer. The following measures can be taken:
① Investigate the load situation of the distribution transformer, including the load 24 hours a day and the load in four seasons a year, find out the general situation of the load, and adjust the three-phase load as much as possible to make it operate as close to symmetrical.
② Adjust the peak and valley time of power consumption to reduce overload; at the same time, increase the capacity of the transformer in time to avoid long-term overload operation of the transformer.
2. Poor grounding
Lightning protection work for distribution transformers that have suffered lightning strikes has generally been done, but there are still two problems: ① Poor grounding of the arrester; ② Only focusing on installing arresters on the high-voltage side, while ignoring the need to install arresters on the low-voltage side (especially Dore area). If the arrester is poorly grounded and overvoltage occurs, the arrester cannot discharge the current well, which will damage the insulation of the transformer; if no arrester is installed on the low-voltage side, when the high-voltage side arrester discharges a large lightning current to the earth, A voltage drop occurs at the grounding position. This voltage passes through the transformer shell and also acts on the neutral point of the low-voltage side winding. The low-voltage side winding is grounded through the wave impedance of the low-voltage line. The following measures can be taken: ① Check the poor grounding related to the arrester and reconnect it as required. Note: First, connect the grounding wire of the arrester directly to the shell of the transformer and the neutral point on the low-voltage side, and then share the grounding device. The grounding resistance should not exceed 4Ω; ② For areas with multiple minefields, a set of low-voltage arresters should be added to the low-voltage side.
3. Oil leakage
Transformer oil leakage is also common in distribution transformers. Due to leakage, the amount of oil in the transformer is reduced, and the oil level is lowered, causing the infiltration of air and water vapor, accelerating the oxidation of the oil and causing its deterioration, increasing the viscosity of the oil, reducing the convection speed, affecting the heat dissipation of the transformer, and causing The temperature rise is higher, which further accelerates the deterioration of the oil. At the same time, the acidity of the deteriorated oil increases, which reduces the insulation resistance of the winding and even damages the insulation. If things go on like this, the transformer will inevitably be damaged. The following measures can be taken: ① Find out where the oil is leaking and deal with it; ② Check whether the transformer oil has deteriorated or deteriorated, and conduct a simple analysis of the oil. If the transformer oil gradually changes from the initial light yellow to orange or brown, and the viscosity of the oil is relatively high, it means that the transformer oil has deteriorated and must be purified or replaced; ③ When the transformer oil has not deteriorated or deteriorated, check the oil level. Too low. If it is too low, add oil to the mark on the transformer oil conservator; ④ Check the insulation resistance of the winding.