Electrode Layout Techniques

Electrode type selection

Select electrode type based on sample shape and testing standards:

Spherical flat electrode: suitable for sheet type specimens (such as 100mm × 100mm × 3mm), the contact pressure between the Φ 6.4mm spherical electrode and the specimen is controlled at (0.8 ± 0.1) N to ensure uniform distribution of the electric field.

Columnar electrode: For thin film or fiber materials, copper cylindrical electrodes (diameter 20mm) are used, with an outer layer wrapped in 2mm thick ceramic dielectric to enhance high temperature and high voltage resistance while reducing electrical discharge effects.

Safety distance: The distance between the high-voltage electrode and the test chamber wall must meet safety standards (such as 100kV equipment ≥ 270mm). During the test, personnel should maintain a distance of at least 1.2m from the equipment to avoid the risk of arc breakdown.

Contact pressure control

Use specialized fixtures to fix the electrodes, ensuring a tight fit with the surface of the sample and avoiding air gaps. Air gaps can cause local electric field distortion, resulting in lower breakdown voltage test values. For example, the contact pressure of a spherical electrode needs to be accurate to 0.8N, which can be calibrated through a pressure sensor.

Sample pretreatment techniques

Cleaning and drying

Cleaning: Dip a silk cloth in a non corrosive solvent (such as ethanol) to wipe the surface of the sample, remove oil stains, dust and other impurities, and prevent the formation of local conductive channels.

Drying: For hygroscopic materials such as polymers, dry at 80 ℃ for 24 hours, then cool to room temperature in a standard environment (temperature 23 ± 2 ℃, humidity 50 ± 5%) to eliminate the influence of moisture on insulation performance. Moisture can lower the breakdown voltage of materials, for example, the breakdown voltage of an undried polyethylene sample may decrease by 30%.

Size and shape control

Thickness uniformity: The thickness of the sample should meet the testing standards (such as 0.1-5mm), with an error controlled within ± 0.1mm. Uneven thickness can lead to electric field concentration, affecting the accuracy of the results.

Edge treatment: Ensure smooth edges and remove burrs and cracks when cutting the sample. For sheet samples, it is recommended to use laser cutting or sandpaper polishing to reduce the risk of partial discharge.

Shape regularity: Priority should be given to circular or square specimens to avoid electric field distortion caused by irregular shapes. For example, the electric field distribution at the electrode edge of a circular sample is relatively uniform, resulting in more stable test results.