Risks of Long-term Transformer Idleness and Re-commissioning Procedures

In general, transformers have a relatively long service life, typically ranging from 20 to 30 years. However, if not used for an extended period, the following issues may arise:

Impact on Windings: When a transformer is not in operation for a long time, the windings can be affected by moisture, dust, or corrosive gases in the environment. The varnish on the windings may harden, leading to a decrease in the insulation capability between windings. Additionally, long-term inactivity may result in winding relaxation or displacement. Any changes in the winding structure can affect the electrical performance of the transformer and may even lead to operational failures.

Impact on the Core: The transformer core, composed of multiple layers of thin steel sheets, plays a key role in enhancing magnetic flux density. If a transformer is idle for an extended period, especially in humid environments, the core is susceptible to rusting due to moisture in the air. This can reduce magnetic flux density, thereby affecting the transformer's efficiency and performance.

Impact on Insulating Oil: Prolonged inactivity can cause the insulating oil to come into contact with air, leading to oxidation. The oxidation of the oil generates acidic substances, which increase the oil's acidity and accelerate its degradation. These acids can also corrode the transformer's internal metal components. Additionally, insulating oil can absorb moisture from the air, increasing its water content. The presence of water reduces the breakdown voltage of the oil, diminishing its insulation performance and increasing the risk of electrical faults. Furthermore, the accumulation of oxidation byproducts and impurities in the oil may form sludge, which reduces heat dissipation efficiency, causing the transformer to overheat during operation and accelerating further oil degradation.

Impact on Mechanical Performance: Tap changer contacts, if not used for a long time, may experience oxidation or corrosion due to moisture, dust, or corrosive gases in the environment. This can lead to poor contact and increased contact resistance, thus affecting the tap changer's adjustment capabilities and operational efficiency. Additionally, several insulating components within the tap changer, such as insulating shafts and insulating supports, may degrade or absorb moisture over time. This reduces their insulating properties, increasing the likelihood of faults.

To prevent these issues, proper storage and maintenance measures should be taken for transformers that are not in use for extended periods. First, the transformer should be stored in a dry, well-ventilated location to effectively avoid excessive humidity problems. Regular inspections and maintenance should also be conducted to check insulation performance and the accumulation of dust, with timely cleaning of any dust buildup. Preventative measures, such as using desiccants or installing dust covers, can also help to prolong the transformer's service life.

Before restarting a transformer that has been idle for an extended period, the following points should be considered:

1.Perform Drying Treatment: Drying the transformer can reduce the impact of moisture ingress into the amorphous alloy, allowing the transformer to operate in a dry state.

2.Remove Internal Dust: Over time, fine dust particles may accumulate inside the transformer due to environmental factors like wind and sand. If this dust accumulates extensively, it can impair the equipment’s performance. Additionally, dust can compromise the equipment's insulation, potentially leading to short circuits. Before re-energizing the transformer, a thorough cleaning should be conducted to ensure there is no dust buildup inside.

3.Pre-Energization Testing: Before putting the transformer back into service, it is necessary to conduct insulation tests, oil quality analysis, and winding resistance measurements. These tests help determine whether the transformer's dielectric strength and leakage current are still within specified standards. Additionally, oil level checks and inspections of buried cable connections should be performed to prevent small issues, such as poor cable connections, from causing major safety incidents upon startup.

In summary, although transformers typically do not deteriorate simply from being idle for extended periods, attention must be paid to moisture and dust accumulation. Regular maintenance and care are essential to ensuring safe, stable, and long-term operation of the transformer.