1. Sample Preparation
Pour the transformer oil sample into a standard test cell. Ensure the oil is representative and free of air bubbles. The oil fills the space between two spherical electrodes.

2. Electrode Configuration
Two spherical electrodes are placed horizontally with a precise gap of 2.5 mm (or 1 mm per standard). Both electrodes are fully immersed in the oil sample.

3. Voltage Ramp
Apply AC voltage (50/60 Hz) at a constant rate (e.g., 2 kV/s). The electric field builds between the spherical electrodes, causing oil molecules to polarize and align.

4. Breakdown Phenomenon
When voltage reaches the oil's dielectric strength limit, oil molecules ionize and form a conductive channel. A visible arc discharge occurs with spark and current surge.

5. Result Recording
The instrument records the breakdown voltage. Typically 6 tests are performed, and the average value is taken as the final result with standard deviation calculated.

6. Oil Quality Assessment
• ≥50 kV: New or reclaimed oil, excellent condition
• 35-50 kV: Acceptable in-service oil
• 25-35 kV: Caution, recommend treatment
• <25 kV: Failed, must replace or regenerate

• Moisture: Trace water significantly reduces breakdown voltage

• Particles: Fibers and metal particles form conductive bridges

• Dissolved Gas: Affects insulating performance

• Temperature: Influences viscosity and water solubility

• Acid Number: Oxidation products degrade insulation