Common Fault Analysis and Operation Maintenance of Power Distribution Transformer Recovery Products:
I. Common Fault Analysis of Power Distribution Transformer Recovery Products
1. Three-phase load imbalance or seasonal overloading
An imbalance in three-phase load distribution is widely prevalent, particularly in rural areas. Most of the electrical load is single-phase, with significant fluctuations. Consequently, many distribution transformers experience an imbalance in three-phase loads, preventing symmetrical operation and generating zero-sequence current. This not only increases transformer losses but also reduces their effective capacity. Both scenarios can lead to overheating, aging of the insulating oil, and a decrease in the insulation level of the windings, ultimately causing transformer damage. Measures that can be taken include:
① Survey the load conditions of the distribution transformer, including loads for all four seasons of the year. Understand the general load situation and adjust the three-phase loads as much as possible to approach symmetrical operation.
② Adjust peak and off-peak electricity usage hours to reduce overloading; at the same time, promptly increase the transformer capacity to prevent long-term overloading.
2. Poor grounding
The lightning protection for transformers struck by lightning generally includes measures, but there are still two issues: ① Poor grounding of lightning arresters; ② Overemphasis on installing lightning arresters on the high-voltage side, while neglecting the need for lightning arresters on the low-voltage side, especially in areas prone to lightning. If the lightning arresters are not properly grounded, during overvoltage events, the arresters cannot ground the current, leading to insulation damage in the transformer; if lightning arresters are not installed on the low-voltage side, when the high-voltage side arresters discharge a large lightning current to the ground, voltage drops occur at the grounding point. This voltage affects both the transformer's casing and the neutral point of the low-voltage winding, which is grounded through the wave impedance of the low-voltage lines. The following measures can be taken:
① Identify and rectify any接地不良 issues related to lightning arresters, and reconnect according to specifications. First, connect the grounding wire of the lightning arrester directly to the transformer's housing and the low-voltage side neutral point, then share the grounding device. The grounding resistance should not exceed 4Ω; ② For areas prone to lightning, an additional low-voltage lightning arrester should be installed on the low-voltage side.
3. Oil leakage
Leakage of transformer oil in distribution transformers is also common. Due to leakage, the oil level inside the transformer decreases, causing air and moisture to seep in, accelerating oil oxidation and deterioration. This increases oil viscosity, reduces convection speed, affects transformer cooling, leading to higher temperature rise, which further accelerates oil deterioration. Additionally, the deteriorated oil becomes more acidic, reducing the insulation resistance of the windings and potentially damaging the insulation. Prolonged exposure will inevitably lead to transformer damage. Measures can be taken as follows: ① Identify and treat the leakage points; ② Check if the transformer oil has deteriorated, and perform a simple analysis. If the transformer oil changes from its initial light yellow to orange, brown, and has a high viscosity, it indicates the oil has deteriorated and must be purified or replaced; ③ When the transformer oil has not deteriorated, check if the oil level is too low. If so, add oil to the marked level in the transformer oil reservoir; ④ Inspect the insulation resistance of the windings.
II. Operation and Maintenance of Distribution Transformer Recycling Products
1. Overload operation of the distribution transformer
Transformer overload operation refers to the load current exceeding the transformer's rated current. Generally, when the transformer operates under low load, its insulation material cannot fully function. However, during continuous overload operation, the transformer generates high temperatures, causing the insulation of the winding to burn hard and fall off, leading to inter-turn short circuits. At the same time, transformer oil produces sludge, which accumulates on the oil tank plates, windings, and cores, resulting in poor oil cooling. This vicious cycle not only severely affects the transformer's lifespan but also causes accidents such as high-voltage breakdown and transformer burnout. Therefore, it is essential to regularly monitor the three-phase load current. The three-phase load currents should strive for consistency, and any deviations should not exceed 10%.
2. Abnormal noises from the distribution transformer
AC current passing through the transformer winding may produce a normal, even "humming" sound due to the iron core's self-vibration. If an abnormal sound occurs, the cause should be investigated and reported to the relevant departments for timely handling. The sound differs when the transformer is no-load and under load. The transformer can only be put into operation after identifying the cause based on the characteristics of the abnormal sound and comparing it with past occurrences.