What factors affect the electrical strength of insulating boards?

  The factors that affect the electrical strength of insulating boards are as follows. In addition to specific requirements for the frequency, waveform, duration of applied voltage, and geometric dimensions of the electrodes, the following points should be noted:

   (1) Sample thickness: When the insulation material is very thin, the breakdown voltage is directly proportional to the thickness, meaning the electrical strength is independent of thickness. As the thickness of the insulation material increases, heat dissipation becomes difficult, leading to a decrease in electrical strength due to factors such as impurities and air bubbles.

  (2) Temperature: The electrical strength decreases as the temperature rises above room temperature.

  (3) Humidity: The entry of moisture into the insulation material reduces the electrical strength.

  (4) Voltage application time: For most organic materials, the electrical strength decreases with increasing voltage application time. During testing, a fast voltage rise rate results in higher electrical strength, while a step-by-step or slow voltage rise with longer duration better reflects the presence of thermal effects and defects such as internal air gaps in the material. Therefore, generally, test methods prohibit the use of impulse voltage application and instead adopt continuous or step-by-step voltage application.

  (5) Mechanical stress or damage: Mechanical stress or damage to the insulation material leads to a decrease in electrical strength. For laminated samples, it is advisable to avoid strong force damage during processing, using milling instead of cutting, and controlling the feed rate to be small.

  (6) Electrodes: In general, a larger electrode area leads to a decrease in breakdown voltage, as larger areas make it easier to find weak points. Additionally, the electrodes should be flat and smooth, without burrs or unevenness, as these factors reduce the accuracy of the test results.

  (7) Water or carbon residue in transformer oil: If the sample is to be tested for breakdown in transformer oil, the transformer oil should meet the standard requirements. Over time, transformer oil absorbs moisture and contains carbon residue from multiple breakdowns, which can reduce the breakdown voltage of the sample. The transformer oil should be treated or replaced in a timely manner.

  (8) Sample cleanliness: The sample should not be contaminated, and thin insulating paper samples should not have wrinkles, as this can reduce the breakdown voltage.