Transformers are the heart of the power system, and the quality of the insulating oil inside them directly affects the stability and safety of the entire power grid. The traditional non-vacuum oil injection method is highly prone to retaining air bubbles, which can lead to partial discharge and insulation faults.
I. Why must "vacuum oil injection" be adopted?
Before answering "How to do it", we must first understand "why it must be done this way". The intricate insulating components and interlayer gaps inside the transformer can easily trap air when oil is injected at normal pressure, forming bubbles that are difficult to expel. These bubbles are lurking "killers" :
Reduce insulation strength: Under high-voltage electric fields, bubbles are prone to ionization, causing partial discharge and gradually eroding the insulation material.
Accelerating oil aging: Partial discharge can generate ozone and nitrogen oxides, polluting transformer oil.
Cause thermal failure: Poor thermal conductivity at the bubble area may lead to local overheating.
Vacuum oil injection is precisely the process of evacuating the transformer body before oil injection to remove the air and moisture inside the tank. In a vacuum environment, oil has stronger permeability and can fully fill every tiny gap, thereby preventing the formation of bubbles and ensuring the absolute safety and long service life of the transformer after it is put into operation.
Ii. Core Steps of Vacuum Oil Injection
A successful vacuum oil injection operation cannot do without a rigorous process and sophisticated equipment. The following is our professional operation process:
The first step: Preliminary preparation and inspection
Oil quality inspection: Conduct a comprehensive laboratory analysis on the newly injected transformer oil to ensure that its key indicators such as breakdown voltage, micro-water content, and dielectric loss factor fully comply with national standards.
Equipment positioning: Connect and inspect the entire system including the vacuum unit, precision oil filter, oil storage tank, vacuum gauge, pipelines and valves, etc., to ensure good sealing and normal operation.
Transformer preparation: Confirm that the valve between the transformer body and the oil storage tank is closed, and reliably connect the dedicated interface for vacuuming the body to the vacuum unit.
Step Two: Vacuuming stage
Start vacuuming: Start the vacuum pump and perform slow and continuous vacuuming on the transformer body.
Achieve and maintain vacuum degree: According to the transformer model and regulations, evacuate the vacuum degree inside the tank to the specified value (usually an extremely high vacuum level, such as <133Pa), and maintain it at this vacuum degree for the specified time (such as 24 hours) to fully remove moisture and gas from the insulation material of the tank.
Step 3: Vacuum oil injection stage
Oil injection: Under the condition of maintaining a high vacuum degree, start the oil filter and inject the qualified oil that has been precisely filtered and degassed through the oil injection valve at the bottom of the transformer.
Key point: Oil must be injected from the bottom! This enables the oil to rise smoothly, facilitating the expulsion of air bubbles adhering to the vessel as the oil surface ascends, rather than being drawn into the oil.
Control the oil injection speed: The oil injection process should be smooth and slow to avoid the oil flow impacting the body. It is generally recommended that the flow rate be controlled at 3000-5000 L/h.
Step 4: Break the vacuum and add oil
Fill the oil to the specified oil level: Stop filling the oil when the oil level approaches the normal oil level in the oil storage tank.
To break the vacuum: Turn off the vacuum pump and slowly inject dry and clean air into the transformer through a dry air filter to break the vacuum state. This step is of vital importance as it can prevent moisture from being sucked back into the tank.
After the oil injection is completed, the transformer needs to be left to stand for a sufficient period of time (usually no less than 24 hours) to allow the extremely trace residual gases in the oil to fully escape. Only then can subsequent tests and operations be carried out.
Vacuum oil injection for transformers is by no means a simple "oiling" process; it is a crucial procedure to ensure the core insulation performance of power equipment. Entrusting it to a professional team is the greatest responsibility for the security of your assets and the stable operation of your power grid.