Insulating oil breakdown voltage tester, also known as insulating oil dielectric strength tester, transformer oil withstand voltage tester, etc., is an instrument for measuring the dielectric strength of insulating oil. To analyze the test results of the oil withstand voltage tester, start with how the insulating oil is broken down:
With the current world's purification equipment after multiple treatment of insulating oil, its water content is often greater than 2mg/kg, and the length of more than 5um impurity particles per 100ml of oil is not less than thousands; in addition, in the process of sampling and measuring, the oil sample is also inevitably in contact with the surrounding atmosphere, and the moisture and dust in the atmosphere will inevitably be immersed in the oil. The impurities in these oils and the water molecules dissolved in the close combination of the oil well and the oil molecules, in the pure oil molecules, far before the polarization and ionization between the electrodes, are arranged and gathered along the electric field strength, and then ionized to form tiny pathways, the so-called "small bridges", the small pathways connect through the two stages, resulting in rapid oil breakdown. The more impurities in the oil, the easier it is to form small bridges and the lower the breakdown voltage. Measuring the breakdown voltage of insulating oil is actually measuring the amount of impurities in insulating oil, that is, judging the degree of contamination of insulating oil.
The breakdown process of oil is actually random and closely related to the instantaneous state of the oil gap electric field. The inhomogeneity of the distribution of impurities in the oil and the movement of the impurity particles cause the distribution of the oil gap impurity particles to change with time, so the position of the bridge in the electric field is unpredictable. Especially for flat chamfered electrodes, the relatively uniform electric field occupies much larger space volume than the electric field of the same intensity formed by spherical and spherical cover electrodes, and the location of small bridges is more unpredictable and the probability of formation is much greater. This is the fundamental reason why the breakdown voltage value of the oil measured by the plate chamfered electrode is lower than that measured by the other two electrodes.
From the above breakdown mechanism analysis, we can know that although the breakdown of the oil gap is a short moment, the process is complex, even if it is a cup of sample, the measured value in multiple breakdown tests is very dispersed, so various test standards are required to take the average of 6 tests as the test results.
Analyze and judge the test results of oil withstand pressure tester:
1. Dispersion of test data
The dispersion of the measured value of 6 breakdown voltage tests of an insulating oil sample is large, and the fundamental reason is that the electric field distribution state between the two electrodes and the distribution state of the impurities contained in the insulating oil at the moment of breakdown are random. In data processing, it is recommended to resample and measure regardless of the standard deviation of 6 data S≥ 10 kV (electrode distance 2.5mm). More precisely, the breakdown voltage value we measured only indicates the probability of electrical breakdown of the insulating oil near the average value, and the probability of electrical breakdown with more high and too low values that deviate from this point is low, not that the insulating oil must be broken down at this point. It is more reasonable to choose the range where the breakdown voltage value is more concentrated, and take the average of no less than 6 measured values as the measurement result, so as to more realistically reflect the average contamination level of the insulating oil.
2. Accuracy of test data
Obtaining accurate and reliable insulating oil breakdown voltage value is the ultimate goal of breakdown voltage test. If there is doubt about the test results, it is recommended to deal with the following methods:
2.1. Check the output voltage waveform and amplitude of the boost device. This work has generally been done by the manufacturer, and the possibility of changes in normal use is not large, and the error caused by no obvious damage in use is very small.
2.2. When the measurement is between qualified and unqualified, the method of comparative test is used to verify the influence of oil cup and electrode on the result, that is, at the same time in different laboratories, different electrodes and oil cups are used to determine the same oil sample, under the premise of ensuring that the distance between the two pairs of electrodes is (2.5±0.1) mm, the higher measured value should be closer to the true value. This is because only the distance between the electrodes is too large will make the error of the breakdown voltage measurement value of the insulating oil positive, and the remaining various influencing factors, including the shape of the electrode, processing accuracy and surface state, the material and shape of the oil cup, etc., will make the measured value have a negative error, that is, the measured result is less than the true value.
After analysis, the main factors affecting the test results of the oil breakdown voltage tester are as follows:
1. Environmental impact
Dust and water vapor in the atmosphere are inevitably immersed in the oil sample to be measured, so that the measured value is low, so the standard has an oil cup plus dust cover and as soon as possible to complete the measurement of the mention, if possible, should be as far as possible in the air conditioning and clean, dry laboratory for measurement, especially in the south of our country wet and rainy season and northern sand and dust season, to prevent environmental conditions on the impact of the measurement results.
2. The influence of test instruments
Oil breakdwon voltage tester includes booster device (manual or automatic), oil cup and electrode, stirring device (manual or automatic), data output device (analog instrument or digital display printer), timing device, etc., each part of the abnormality will make the measurement results error, automatic instrument is better, in the measurement process basically eliminate the influence of factors considered.
2.1. Oil cup and electrode
The shape of the electrode is different, the electric field of the space around the electrode is also completely different, the electric field between the plate chamfered electrode can be roughly regarded as a uniform electric field, and the electric field between the spherical and spherical cover electrodes is an inhomogeneous electric field, and the insulating oil behaves almost differently in different electric fields. The capacity of the oil cup and the depth of immersion of the electrode in the insulating oil will affect the measurement results, which are clearly specified in the relevant standards. Practice has proved that the processing and assembly level of the electrode, the shape and material of the oil cup and other differences will bring obvious differences to the measurement results.
2.2. Booster device
Whether the output voltage waveform of the boost device is similar to a sine wave, whether the output voltage is displayed with the output, has a great impact on the accuracy of the results, and the performance of the booster device of different test instruments must ensure that it meets the provisions of the standard. This performance of the booster device should be guaranteed by the manufacturer in the design and production of the instrument.
Kingrun model JY6611 insulation oil breakdown voltage tester (oil BDV tester,oil dielectric strength tester), 80KV and 100KV available, Electromagnetic compatibility concept,follows standard IEC 156 ,ASTM D877,ASTM
D1816,VDE0370.
The unique advantage of this instrument is that the built-in electronic boost system makes the measured data more
accurate and efficient.Built-in advanced insulating material and the heat dissipation system protects the safety of
operators and prolongs the service life of the instrument.
