What are the factors that cause dielectric loss of insulating oil filter
2018/5/17 Viewers:
The main factors affecting the dielectric loss factor of oil are the following factors.
(1) in relation to the applied voltage and frequency, when the dielectric loss factor is measured, the voltage has no doubt on the dielectric loss factor when the dielectric loss factor is measured. But when the test voltage is increased, the dielectric loss is caused by the dipole transfer under high voltage, and the loss of the dielectric will increase obviously. Therefore, dielectric loss factor increases with the increase of voltage. Therefore, when measured, the voltage should be added to the rated voltage. It is introduced that when the dielectric loss factor is measured, the voltage must be added to 3kV to 10kV before the true value can be detected, otherwise the error will be larger. The dielectric loss factor is also related to the frequency of the applied voltage, because the change of the tangent value of the dielectric loss angle is the function of the frequency, that is, the loss angle of the medium varies with the frequency. Therefore, when the dielectric loss factor is generally measured, the AC voltage of 50Hz is adopted, which also conforms to the actual use of the electrical equipment.
(2) temperature has a great influence on the measurement results of dielectric loss factor. If the temperature difference between measurements is several degrees, the result of parallel test is not consistent. Because the conductance of the medium varies with temperature. Therefore, when the temperature increases, the conductance of the dielectric will increase, and the leakage current will also increase, so the dielectric loss factor will also increase. Practice has proved that the higher the temperature, the better the difference between good oil and bad oil. If there is almost no difference between the oil samples at 60, and the difference between them will be apparent at 100C, so the measurement of the loss factor of the oil medium should be carried out from 80 to 100C. Therefore, in the "GB test method", the test temperature is changed from the original "70C" to "90C". Of course, the higher the temperature is, the greater the loss factor of the medium, but the higher the temperature can promote the aging of the oil, it will also affect the test results, so the temperature must not be unrestricted.
(3) because of the strong polarity of water, polarization is easily induced by electric field, and the conductance current of oil increases, which causes the dielectric loss factor of oil to increase obviously. At the same time, the humidity is also related to the measurement. Normally, the increase of humidity will increase the dissolved water of oil sample (oil induced by moisture) and increase the medium loss factor. Therefore, the determination should be carried out under the specified relative humidity.
(4) it is related to the degree of oil purification and the depth of aging. The magnitude of the dielectric loss factor of the oil indicates that it is independent of the chemical composition of the oil, but is related to the degree of purification of the oil. If the oil is refined or regenerated, because of the incomplete purification, the remaining organic acids and metal soaps are retained in the oil, which can easily polarize under the action of the electric field, increase the conductivity of the oil, and increase the dielectric loss factor of the oil. The dielectric loss factor of oil is also related to the aging depth of oil. The deeper the aging degree of oil is, the more organic acids and other aging products in the oil are found. These aging products will increase the conductivity current of the oil under the action of electric field, and increase the dielectric loss of oil.
(1) in relation to the applied voltage and frequency, when the dielectric loss factor is measured, the voltage has no doubt on the dielectric loss factor when the dielectric loss factor is measured. But when the test voltage is increased, the dielectric loss is caused by the dipole transfer under high voltage, and the loss of the dielectric will increase obviously. Therefore, dielectric loss factor increases with the increase of voltage. Therefore, when measured, the voltage should be added to the rated voltage. It is introduced that when the dielectric loss factor is measured, the voltage must be added to 3kV to 10kV before the true value can be detected, otherwise the error will be larger. The dielectric loss factor is also related to the frequency of the applied voltage, because the change of the tangent value of the dielectric loss angle is the function of the frequency, that is, the loss angle of the medium varies with the frequency. Therefore, when the dielectric loss factor is generally measured, the AC voltage of 50Hz is adopted, which also conforms to the actual use of the electrical equipment.
(2) temperature has a great influence on the measurement results of dielectric loss factor. If the temperature difference between measurements is several degrees, the result of parallel test is not consistent. Because the conductance of the medium varies with temperature. Therefore, when the temperature increases, the conductance of the dielectric will increase, and the leakage current will also increase, so the dielectric loss factor will also increase. Practice has proved that the higher the temperature, the better the difference between good oil and bad oil. If there is almost no difference between the oil samples at 60, and the difference between them will be apparent at 100C, so the measurement of the loss factor of the oil medium should be carried out from 80 to 100C. Therefore, in the "GB test method", the test temperature is changed from the original "70C" to "90C". Of course, the higher the temperature is, the greater the loss factor of the medium, but the higher the temperature can promote the aging of the oil, it will also affect the test results, so the temperature must not be unrestricted.
(3) because of the strong polarity of water, polarization is easily induced by electric field, and the conductance current of oil increases, which causes the dielectric loss factor of oil to increase obviously. At the same time, the humidity is also related to the measurement. Normally, the increase of humidity will increase the dissolved water of oil sample (oil induced by moisture) and increase the medium loss factor. Therefore, the determination should be carried out under the specified relative humidity.
(4) it is related to the degree of oil purification and the depth of aging. The magnitude of the dielectric loss factor of the oil indicates that it is independent of the chemical composition of the oil, but is related to the degree of purification of the oil. If the oil is refined or regenerated, because of the incomplete purification, the remaining organic acids and metal soaps are retained in the oil, which can easily polarize under the action of the electric field, increase the conductivity of the oil, and increase the dielectric loss factor of the oil. The dielectric loss factor of oil is also related to the aging depth of oil. The deeper the aging degree of oil is, the more organic acids and other aging products in the oil are found. These aging products will increase the conductivity current of the oil under the action of electric field, and increase the dielectric loss of oil.
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