Common Fault Analysis and Operation & Maintenance of Distribution Transformer Recycling Products:
I. Common Fault Analysis of Distribution Transformer Recycling Products
1. Three-phase load imbalance or seasonal overloading
An imbalance in three-phase loads is widely prevalent, especially in rural areas, where a significant portion of the power load is single-phase and experiences considerable fluctuations. As a result, many distribution transformers suffer from unbalanced 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 of transformers, 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 Investigate the load conditions of the distribution transformer, including loads across the 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 times to reduce overloading; simultaneously, promptly increase the transformer capacity to prevent long-term overloading operation.
2. Poor grounding
The lightning protection work for transformer substations struck by lightning is generally in place, 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 them on the low-voltage side, especially in areas prone to lightning strikes. If the lightning arresters are not properly grounded, during overvoltage events, the arresters cannot ground the current, potentially damaging the transformer's insulation. 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, while affecting the transformer's casing, also acts on the neutral point of the low-voltage winding, which is grounded through the wave impedance of the low-voltage lines. Measures that can be taken include:
① Identify and rectify any poor grounding issues related to the lightning arresters, and re-wire according to specifications. Note to first connect the grounding wire of the lightning arrester directly to the transformer's casing and the neutral point of the low-voltage side, then share the grounding system. The grounding resistance must 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, allowing air and moisture to seep in, which accelerates oil oxidation and degradation. This increases oil viscosity and reduces convection speed, affecting the transformer's heat dissipation, leading to higher temperature rise, which further speeds up oil degradation. Additionally, degraded oil becomes more acidic, reducing the insulation resistance of windings and potentially damaging the insulation. Prolonged exposure will inevitably lead to transformer failure. Measures can be taken as follows: 1. Identify and properly address the leakage sites; 2. Check if the transformer oil has degraded, and perform a simple analysis. If the oil changes from its initial light yellow to orange and brown, and has a high viscosity, it indicates that the transformer oil has degraded and must be purified or replaced; 3. When the transformer oil has not degraded, check if the oil level is too low. If it is, add oil to the marked level in the transformer's oil reservoir; 4. Inspect the insulation resistance of the windings.
Section II: Operation and Maintenance of Power Distribution Transformer Recycling Products
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 deviation should not exceed 10%.
2. Abnormal sound from the distribution transformer
When alternating current passes through the transformer winding, a normal, even "humming" sound is produced due to the iron core's natural vibration. If an abnormal sound occurs, the cause should be investigated and reported to the relevant departments for immediate action. The sound differs when the transformer is no-load and under load. The transformer should only be put into operation after identifying the cause based on the characteristics of the abnormal sound and comparing it with previous occurrences.