ASTM D924 Standard Test Method for Dissipation Factor (or Power Factor) and Relative Permittivity (Dielectric Constant) of Electrical Insulating Liquids

Get Certified ASTM D924 Testing for Reliable Insulating Liquid Assessment

The performance and reliability of electrical insulating liquids are related to the dissipation factor and relative permittivity. ASTM D924 certification provides a quality control test for insulating liquids used in electrical apparatus. Qualified laboratory testing provides accurate, repeatable data for quality control, condition monitoring, and contamination/deterioration. This testing supports maintenance decisions and helps ensure reliable operation of transformers, cables, and circuit breakers. 

 The scope of ASTM D924 includes:

• Material type: This is for electrical insulating liquids (mineral insulating oil, silicone liquids, or other liquid dielectrics used in electrical apparatus).
• Purpose: ASTM D924 determines the dielectric loss characteristics and permittivity of insulating liquids to evaluate their quality and condition.
• Property measured: Dissipation factor/power factor, relative permittivity/dielectric constant.
• Method: This test determines the loss characteristics and permittivity at commercial frequencies with an appropriate test cell and measuring equipment (ASTM D924). 
• Result: The testing laboratory obtains dissipation factor and relative permittivity values from the liquid samples it tests.
• Test Limitations: Reference procedures at 45 Hz to 65 Hz. Some changes are allowed for standard determinations that do not need high accuracy.
• Environmental conditions: Test conditions comprise controlled laboratory conditions for accurate measurements of the dielectric. 
• Applications: ASTM D924 is used for quality control of new insulating liquids, condition monitoring of in-service liquids, and to assess changes due to contamination or deterioration. 

What are the Uses of ASTM D924 Testing?

ASTM D924 testing provides reliable dielectric property data to assess an insulating liquid’s quality. Manufacturers and engineers use these results for quality control, condition monitoring, and maintenance decisions.

This standard-

• New electrical insulating liquids quality control
• In-service insulating liquids: condition monitoring of in-service insulating liquids
• Locating faults in transformers, cables and circuit breakers
• Assessing  the effectiveness of liquid treatment processes
• Supporting working practices for maintenance/replacement of electrical apparatus
• Providing data for dielectric loss assessment and permittivity measurement 

Which materials can be tested under ASTM D924?

ASTM D924 covers the following electrical insulating liquids: mineral insulating oils, Silicone liquids, and other liquid dielectrics. It applies to new liquids and liquids used in cables, transformers, oil circuit breakers, and other electrical apparatus.

Why is ASTM D924 Important?

ASTM D924 is the standard test for the dissipation factor and relative permittivity of electrical insulating liquids. Dissipation factor measures dielectric loss and serves as a quality-control indicator that may signal deterioration, processing issues, or contamination. Relative permittivity influences the electrical properties of an insulation system or a capacitor dielectric. This standard enables accurate condition assessment, supports maintenance decisions, and helps ensure reliable operation of electrical apparatus.

ASTM D924 Testing Process and Data Collection

Testing follows Practice D923 and involves taking a representative sample of the insulating liquid. Technicians clean and fill the test cell, ensuring no contamination affects the data. The sample is brought to the required test temperature, and the technicians take measurements at a commercial frequency range of 45Hz to 65Hz. The measuring equipment measures the dissipation factor and relative permittivity of the liquid. The data acquisition system is used to record the values and the laboratory report results for quality control or condition assessment. 

Common Challenges and Troubleshooting in ASTM D924

Due to the complexity of ASTM D924, the handling of test samples and preparation of the test cell are critical to obtaining accurate results. Contamination from the cell or sample affects measurements. The method includes all the steps necessary to clean and fill the test cell, particularly in the context of avoiding contamination. Accurate measurements of the dielectric properties require temperature control. Laboratories obtain consistent data if they prepare samples carefully, use calibrated equipment, as per practice D2865, and have standardized test conditions and trained technicians working under standardized procedures. 

• Test results report dissipation factor or power factor as a decimal value or percentage (%) to indicate the dielectric loss characteristics of the insulating liquid.
• Analysts report relative permittivity, also called dielectric constant, as a dimensionless value that characterizes the liquid’s ability to store electrical energy.
• The laboratory interprets lower dissipation factor values as lower dielectric losses under the specified test conditions, while considering the applicable insulating-liquid requirements.
• Analysts compare dissipation factor and relative permittivity with baseline or previous measurements to identify changes that may indicate contamination, degradation, or processing effects.
• Engineers compare the measured dielectric properties with applicable specifications for the insulating liquid and use the results to support quality-control and condition-monitoring decisions for electrical apparatus.

Link to ASTM D924