Oil Tan Delta Testing

Oil tan delta testing, also known as dissipation factor testing, is a powerful method used to evaluate the quality and condition of insulating oils. In electrical systems and equipment, ensuring the integrity and reliability of insulating oils is significant for maintaining optimal performance.

Transformer Oil and its Key Parameters

The conventional technology and formulation used in insulating fluids have remained largely unchanged for nearly 100 years. The composition is characterized by:

• Wide range of applications, suitable for various types and models of transformers as well as other power equipment.
• High electrical insulating properties that ensure reliable performance.
• Low viscosity and excellent thermal conductivity, contributing to efficient cooling of electrical units.
• Low pour point, allowing for use in all climatic regions.

Dielectric fluids are intended to perform the following basic functions:

Insulating: dielectric fluids are used to provide insulation between various pieces of electrical equipment such as wires, coils, and transformers. They prevent short circuits and current leaks, which can lead to overheating and equipment damage.

Cooling: dielectric fluids provide effective cooling of electrical equipment by transferring heat from hot components to cooler ones. This helps maintain a stable operating temperature and extends the service life of equipment.

Lubricating: insulating oils serve as lubricants for moving parts of electrical equipment such as fans and pumps. It helps reduce friction and wear, and prevents corrosion of metal components.

Sealing: oils are used as sealing materials in electrical units such as transformers and capacitors to prevent moisture and contaminants from entering the equipment.

Dielectric Strength: oils have a high dielectric strength, meaning they can withstand high voltages without dielectric breakdown. This ensures reliable insulation performance and protection against electrical discharges and overvoltages.

Transformer oil is produced according to strict technical regulations, with defined grades that conform to standardized formulations. The chemical composition and performance requirements have remained consistent for nearly a century, ensuring reliability across various types of transformers and other power equipment. It offers a wide range of applications, excellent electrical insulation, low viscosity for efficient heat dissipation, and a low pour point, making it suitable for use in different climates. Furthermore, its cost-effectiveness makes it a widely used choice in the power sector.

Dielectric Loss Tangent: Physical Meaning and Quality Assessment of Transformer Oil

The oil tan delta value (tgδ) is a key criterion for evaluating the dielectric properties of oils and their compatibility when mixed. It is also used to assess the degree of aging and to detect the presence of various chemical contaminants, including insulation degradation and aging products.

The tan delta value (tgδ) is highly sensitive to impurities, such as colloidal formations, dissolved metal-organic compounds, and various oxidation products.

An increase in dielectric losses occurs due to the presence of asphaltic and resinous substances that form colloidal solutions in the oil, as well as soaps, water (except when fully dissolved at a molecular level), acids that become active at elevated temperatures, and dissolved transformer varnishes. These constituents typically increase the acid number.

Types of Colloidal Contaminants

Colloidal substances in transformer oil may include:

• Constituents of transformer winding varnish and aged sludge deposits.
• Soaps formed due to reactions between acidic degradation products and transformer metals.
• Acidic sludge-like compounds that contain no metals, such as poorly soluble acids, resins, asphaltenes, and other oxidation products.

For new transformer oil, the tan delta value (tgδ) reflects the quality of purification at the production stage. During operation, it indicates contamination levels and aging effects. The advantage of oil tan delta testing resides in its ability to detect even minimal changes in oil properties that might go unnoticed during standard chemical tests.

The way the tan delta value (tgδ) changes with temperature provides essential insights into the type of contaminants present. If the tan delta value (tgδ) is high at indoor temperature, but acceptable at elevated temperatures, this suggests the presence of polar impurities, such as suspended water droplets. If the tan delta value (tgδ) remains high across a wide temperature range, it indicates more extensive contamination. The presence of water in oil leads to a characteristic U-shaped tangent delta vs temperature curve, which exhibits a minimum at approximately 50 °C.

By analyzing oil tan delta and its temperature dependence, it is possible to identify early signs of oil degradation and take timely measures to maintain the reliability of transformer insulation.

Procedure of oil tan delta testing

Oil tan delta testing is typically conducted at 194 °F, but it may also be performed at different temperatures (e.g., 68 °F, 122 °F, and 158 °F) when required. At 50 Hz, the tan delta value (tgδ) is primarily determined by electrical conductivity of oil. The factors affecting the tan delta value include contaminants that increase electrical conductivity, such as colloid particles, dissolved organometallic compounds (soaps), and resinous substances formed due to oil aging, oxidation, and polymerization reactions.

Oil tan delta testing allows for detecting even minimum contamination levels that cannot be identified by chemical methods. Furthermore, analyzing the temperature dependence of tan delta helps determine the nature of contaminants, providing valuable insights into oil degradation and its impact on equipment reliability.

Advantages of the FLD T Tester

At present, oil tan delta testing with periodic monitoring usually involves the use of portable devices.

The FLD T tester is an advanced device for testing the tan delta, permittivity, and electrical resistivity of transformer oils and other dielectric fluids. It operates in full compliance with international standards such as IEC 60247-2004-02, ASTM D924-08, and ASTM D1169-02. This tester offers several advantages for monitoring the quality of high-voltage insulation.

One of the key features of FLD T oil tan delta testers is automatic measurement of insulation condition. This ensures early detection of potential issues, alerting the operators when the insulation is close to failure. This compact unit enables analyzing an important parameter — the dielectric loss tangent of transformer oil — at a standard industrial frequency, in full compliance with IEC 60247. It features built-in volatile memory. The FLD T tester also allows for PC connectivity with the use of dedicated software.

Key Specifications:

• Measurement range for dielectric loss tangent: 0.0001 to 4.0
• Applied AC voltage: sinusoidal, 500–2,000 V
• Measurement range for electrical capacitance: 20–1,000 pF
• Oil temperature range: 68–230°F

Сombining high precision, ease of use, and integration capabilities, the FLD T tester provides a reliable solution for assessing the condition of transformer oils and dielectric fluids, which helps ensure the operational life and safety of electrical equipment.