Strictly speaking, pure transformer oil containing no impurities such as moisture, dust, and fibers, breakdown begins with the polarization and ionization of individual oil molecules in the electric field, and its chemical composition has little effect on the breakdown voltage.
Different grades and origins
The transformer oil should have approximately the same breakdown voltage, and the dispersion of the parallel test results of the same sample is not large, but the transformer oil and the “purified transformer oil” in actual applications are quite different, even though the world’s most advanced.
The transformer oil after several purifications of the purification equipment often has a moisture content of more than 2 mg/kg, and there are not less than several thousand impurity particles with a length greater than 5 μm per 100 mL of oil; in addition, the transformer oil sample is inevitable during sampling and determination. In contact with the surrounding atmosphere, moisture and airborne dust in the atmosphere are inevitably mixed in. The impurities in these transformer oils and the water molecules dissolved in the transformer oil and tightly bound to the oil molecules are far from the electrode in pure oil molecules. Before polarization and ionization, they are arranged and concentrated along the direction of the electric field strength, and then ionized to form tiny paths, the so-called “small bridges” and small passes. The connection penetrates through both poles and causes rapid oil breakdown.
The more impurities in the transformer oil, the easier it is to form a small bridge and the lower the breakdown voltage. The breakdown voltage of the transformer oil is actually a measure of the impurity content of the transformer oil. That is to say the degree of contamination of the transformer oil.
The JY6611 transformer oil breakdown voltage tester provided by Kingrun Instruments has a stable voltage regulator power supply. Its waveform quality is good and its electromagnetic compatibility design is perfect. This avoids the influence of grid voltage fluctuations, so the test results are more accurate.