Factors Affecting the Breakdown Voltage of Transformer Oil: Considerations for Equipment Procurement

It's essential to understand how the breakdown voltage of transformer oil influences equipment selection, especially from a procurement perspective. Breakdown voltage is a critical parameter that reflects the oil's ability to withstand electrical stress without failure, making it a vital factor when specifying equipment for transformers.

Here are the key factors affecting the breakdown voltage of transformer oil and how they impact equipment selection:
 

1. Moisture Content
Moisture is one of the most sensitive factors that influence the breakdown voltage of transformer oil. Water in the oil, either as free water, dissolved water, or in an emulsified state, can significantly lower the oil's dielectric strength. This happens because water molecules are polar, and when aligned in an electric field, they can form a conductive bridge between electrodes, causing the oil to break down at a lower voltage.

Procurement Consideration:

Oil Treatment Equipment: For high-voltage transformers, procurement should focus on specifying oil treatment systems that effectively remove moisture (dehydration units, vacuum dehydration processes) to ensure the oil maintains a high breakdown voltage.
Moisture Monitoring Systems: It is crucial to procure transformers equipped with moisture detection systems or moisture-in-oil analyzers to monitor and maintain optimal oil condition throughout the equipment’s lifecycle.

2. Air Bubbles in the Oil
Even a small amount of air bubbles in the oil can drastically reduce its breakdown voltage. Air bubbles lower the dielectric strength because they act as weak points where electrical discharges can occur more easily.

Procurement Consideration:

Degassing Systems: Transformers or oil treatment equipment with degassing systems should be specified to ensure the removal of entrained air or gas from the oil.
Oil Handling Procedures: Proper handling and filtration equipment should be part of the procurement to prevent air bubbles from being introduced during oil filling or maintenance.

3. Temperature
Temperature has varying effects on breakdown voltage, depending on the presence of impurities and moisture. In pure oil, temperature increases can lead to molecular ionization, which can reduce breakdown voltage. If impurities or moisture are present, a rise in temperature can increase bubble formation and decrease the oil’s dielectric strength.

Procurement Consideration:

Temperature Management: Equipment with advanced temperature control systems should be procured to manage oil temperature effectively. Transformers should include monitoring and cooling systems designed to minimize the risk of thermal degradation of the oil.
Thermal Stability: When procuring oil and insulation materials, look for specifications that offer high thermal stability to reduce the risk of ionization and maintain dielectric strength at elevated temperatures.

4. Impurities and Free Carbon
If the oil contains impurities such as carbon particles or other solid contaminants, its breakdown voltage will be reduced. Carbon particles, especially, form conductive paths under an electric field, lowering the oil's ability to insulate properly.

Procurement Consideration:

Oil Purification Systems: Transformers should include purification systems or processes (e.g., oil filtration and centrifugation) to remove impurities and suspended particles.
High-Quality Oil: Specify high-quality transformer oils from reputable suppliers that adhere to strict cleanliness and purity standards. Procurement should prioritize oil that meets international standards like IEC 60296.

5. Oil Aging and Acidity
As transformer oil ages, it can produce acidic by-products that affect its ability to maintain dielectric strength. While acids themselves may not immediately lower the breakdown voltage, they contribute to the emulsification of water, which can decrease the oil’s dielectric strength over time. In aged oil, the dielectric loss factor may rise, affecting overall transformer performance.

Procurement Consideration:

Monitoring Systems for Aging Indicators: Equipment with oil aging monitoring, including acidity and dielectric loss factor measurement systems, should be part of the procurement process. These features allow for proactive maintenance and oil replacement strategies.
Preventive Maintenance Programs: In procurement contracts, ensure there is a robust preventive maintenance program, including oil testing services that focus on dielectric strength, acidity, and other oil degradation markers.

 

Conclusion

From a procurement perspective, understanding the factors that affect the breakdown voltage of transformer oil is crucial for selecting the right equipment. Transformers need to be specified with features such as advanced oil treatment systems, moisture and impurity control, temperature regulation, and aging monitoring. These considerations ensure not only the reliable performance of the transformer but also reduce long-term maintenance costs and extend the life of both the oil and the transformer. Ensuring the procurement of high-quality transformer oil and equipment designed to maintain optimal oil conditions is key to maintaining high dielectric strength and ensuring the operational safety and efficiency of the electrical system.