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A measurement of dielectric loss tangent of TG what is the significance?
Dielectric loss tangent of dielectric loss and dielectric loss factor or. Measurement of dielectric loss factor is a very high sensitivity test project, it can be found that the insulation of power equipment as a whole is affected by moisture, deterioration of mass and small volume of test equipment through and not through the local defect. For example: the casing of a transformer, the normal TG value is 0.5%, and when the TG value is 3.5%, 7 times the difference between the two data, and the measurement of insulation resistance, moisture before and after the numerical difference is not.
The measurement of dielectric loss factor has high sensitivity to the reflection of the defects, so it has been widely used in electrical equipment manufacturing and power equipment handover and preventive test. Transformer, generator, circuit breakers and other electrical equipment, the dielectric loss test "procedures" have been made.
Two. The current status and technical difficulties of the current domestic dielectric loss tester?
Dielectric loss tester technology develops very quickly, is widely used in power system before QS1 Schering bridge is being instead of intelligent type of dielectric loss tester, a new generation of dielectric loss tester are built-in boost device and a standard capacitor, and has simple operation, accurate data, test result is read convenient wait for a characteristic. Although the current dielectric loss test technology has developed rapidly, but compared with the international level, there is still a big gap in many aspects, the gap is mainly reflected in the following aspects:
(1) anti interference ability
Due to the dielectric loss measurement is a high sensitivity, so the test data also easily interfered by external electric field, taken in the dielectric loss tester anti-interference methods mainly include: phase inversion method, phase shifting method, different frequency method. Although these methods can solve the problem of interference to a certain extent, but when the external disturbance is strong, it will still have a large deviation.
(2) the test accuracy of reverse connection
Site a lot of power equipment have been ground. Therefore, it is necessary to use reverse connection method were detected, but reverse connection, there are many factors that influence the testing data often data will have a large bias, especially when subjects product capacity of smaller, such as casing, a high-voltage wire mopping the floor test (some dielectric loss tester with high-voltage wire although mopping the floor use, but the leakage current) is large, will seriously affect the test accuracy.
Three. What is the "full automatic anti interference source", compared with the other kinds of anti-jamming methods have the characteristics of what?
So-called "full automatic anti interference source, namely inside the instrument has a set of detection device, can detect the amplitude and phase of the interference signals, transmits information related to the CPU, the CPU output commands to the" anti interference source control device, the device will be in the interior of the instruments produce a and dry disturbance signal amplitude identical but opposite to the phase of the "anti interference signal and interference signal superposition offset to achieve anti-jamming. Due to the whole test process, the "anti interference source" automatically generated, the user does not need to intervene, we call the "full automatic anti interference source" ".
Four. Traditional anti-interference methods include phase inversion method, phase shifting method, measuring method, the working principle of how to?
1, reverse phase method
The instrument working power supply is positive and inverse two times of reverse phase test, the two test results are analyzed and processed to achieve the purpose of anti interference, the method has a certain effect in the case of weak external interference.
2, phase shift method
Ideas due to the phase inversion method ", but the working power supply of the inverted phase change is to the phase shifting interference signal are the same and to reduce the influence of interference. The practice shows that under the strong interference, the data is still a big deviation.
3, different frequency method
This is a method developed in recent years. Its basic principle is the working power supply frequency is 50Hz, namely with the frequency of different, so that the sampled signal of two different frequency signal (test current and interference current superimposed, through the analog filter and digital filter for signal filtering, attenuation frequency signal, in order to achieve the purpose of anti-interference. The practice shows that the method of anti-interference ability is better than the "reverse phase method" and "phase shift", but in certain circumstances, due to the influence of interference data still have deviation, and even negative. In addition, because of its own characteristics, there are several aspects of the contradiction:
(1) the choice of frequency: the closer the frequency and frequency, the weaker the ability to resist interference, but the better the equivalent; frequency and power frequency, the stronger the ability to resist interference, but the less effective.
(2) in order to enhance the equivalence, some instruments use a "double frequency", you can choose two kinds of frequency test, such as 60Hz and 40Hz, but the problem is not consistent with the results of the two frequency test how to do? For simple average processing power and power frequency equivalent?
(3) the analog filter has the phase shift problem, the fixed phase shift can be compensated by the computer, but when the temperature and other conditions change caused by the phase shift characteristic changes, it will seriously affect the test results of the dielectric loss value.
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