The tracking test is a core method to measure the tracking resistance of electrical insulation materials. Its result evaluation directly determines the safety level of materials. Scientific evaluation requires combining physical observation, electrical parameter analysis and standard comparison to verify material resistance from multiple dimensions, providing key basis for safe design of electrical equipment.

1. Key Evaluation Indicators of Tracking Test

Three core indicators focus on tracking test result evaluation. First is the critical tracking value, the voltage or time when the first continuous conductive trace (resistance ≤0.5MΩ) forms on the material surface. It directly reflects the anti-tracking threshold. For example, at 1000V, materials without tracking within 30 minutes have significantly higher resistance than those tracking in 15 minutes.

Second is the erosion degree, evaluated by measuring the area, depth and spread speed of carbonized areas on the sample surface. High-quality insulation materials only show slight local carbonization after testing. Poor materials may form through conductive channels with erosion depth exceeding 50% of material thickness.

Third is electrical parameter stability, including leakage current fluctuation and arc discharge frequency during testing. Stable materials should have current fluctuation ≤5mA without continuous arcs; if current surges over 10mA with continuous arcs, the material has lost insulation capability.

2. Core Evaluation Process and Operating Specifications

The evaluation process follows the three-step logic of "phenomenon observation-parameter verification-standard comparison". Firstly, conduct appearance inspection: observe the sample surface with a 50x microscope, record the shape (dendritic/reticular), distribution range of conductive traces and whether a closed loop is formed. Pay special attention to carbonization near electrodes, the electric field concentration area most prone to tracking.

Secondly, perform electrical performance retesting. Within 24 hours after testing, measure the sample surface resistance with an insulation resistance meter. If resistance ≤1MΩ for over 1 minute, judge as "tracked". Meanwhile, check the dielectric loss factor change; an increase over 20% from the initial value indicates hidden electrical aging.

Finally, conduct standard compliance judgment: classify materials into grades 0-6 according to IEC 60112. For example, materials passing 600V test without tracking are graded 3, suitable for medium and high-voltage electrical equipment; those only passing 100V test are grade 0, prohibited for live part insulation.

3. Common Interference Factors and Elimination Methods

Three interference factors need attention in evaluation. Electrode contamination is the primary hazard: electrolyte crystals on platinum electrodes cause local electric field distortion, forming false tracking. Solution: clean electrodes with anhydrous ethanol after each test and dry with an infrared lamp.

Environmental humidity fluctuations also affect results. When relative humidity exceeds 85%, increased surface water absorption accelerates tracking. Record ambient humidity during evaluation; if deviating from standard conditions (65±5%), calibrate results with humidity correction formulas.

In addition, electrolyte concentration deviation (standard is 0.1% ammonium chloride solution) changes conductivity. It is recommended to test each batch with a conductivity meter, ensuring conductivity within 1.0-1.2mS/cm; otherwise, reconfigure.

4. Practical Significance of Standardized Evaluation

Unified evaluation standards ensure result comparability. IEC requires consistent evaluation criteria across laboratories: tracking is defined as "continuous conductive trace length ≥10mm and resistance ≤0.5MΩ" to avoid deviations from subjective judgment.

For batch testing, use statistical analysis: calculate the standard deviation of 10 samples in the same batch. A standard deviation ≤5% indicates consistent qualification; abnormal data (deviating ±15% from the average) requires checking sample preparation defects (e.g., surface scratches) or equipment failures (e.g., unstable voltage output).

Scientific evaluation not only screens qualified materials but also promotes material improvement through failure mode analysis. For example, frequent tracking at electrode edges can guide manufacturers to optimize formulas, increasing arc-resistant additives in edge areas. This "test-evaluation-improvement" cycle is the core value of tracking tests.