I have been using the insulation oil tester for several years, and many colleagues say they know the operation process, but they are not quite sure what happened inside the instrument. Understanding the principle is not about showing off skills, but about being able to determine whether the problem is with the instrument, the oil sample, or the operation when there is a real issue.

Basic principles of testing

The breakdown voltage test of insulating oil is to apply gradually increasing AC voltage to the oil sample under standard conditions until insulation breakdown occurs in the oil film between the two electrodes, and record the voltage value at this time. At the moment of breakdown, the oil film resistance suddenly drops, and a large current rushes through the gap. The instrument automatically detects this sudden change and records the breakdown voltage, then cuts off the high voltage to prevent continuous arc damage to the electrode.

Why use AC instead of DC

The breakdown mechanism of insulation oil by AC voltage is closer to the actual working conditions of transformers (power frequency AC operation), and the reference significance of the test results is stronger. The national standards GB/T507-2002 and IEC 60156 both stipulate the use of AC voltage at 50Hz for testing the dielectric strength of insulating oil. The boost frequency of HZJQ-X1 is accurate to 50Hz, with a voltage distortion rate of<3%, ensuring that the testing conditions are consistent with the standard.

Standard regulations for boost speed and electrode spacing

These two parameters directly affect the test results and cannot be set arbitrarily. The boost speed of HZJQ-X1 can be adjusted between 0.5kV/s and 5.0kV/s, and different execution standards correspond to different boost speed requirements. The electrode spacing is usually 2.5mm, and it needs to be adjusted with a randomly attached standard gauge - if the electrode spacing is too large, the breakdown voltage will be higher; The spacing is too small, the result is too low, and the error directly affects the judgment.

Why do we need to measure multiple times and take the average

The results of breakdown voltage measurement for the same cup of oil sample are not completely the same each time, because each breakdown will produce trace carbon particles in the oil, changing the local state of the oil; The random distribution of bubbles in the oil also affects each result. HZJQ-X1 supports 1 to 10 cycles of testing and automatically calculates the average value. Industry standards usually require taking the average of 6 cycles in order for the results to have statistical significance. The reference value of a single result is limited.

The function of stirring

Between two breakdowns, the instrument automatically stirs the oil sample to evenly disperse the carbon particles and bubbles generated by the breakdown, allowing the oil sample to return to a relatively uniform state before the next test and reducing the low results caused by local carbon particle accumulation. The stirring time can be adjusted from 0 to 120 seconds to meet the requirements of different standards.