Analyze the difference between the indication values ​​measured by different types of loop resistance testers

Due to the non-ideal voltage source of the loop resistance tester test power, the different resistance Rm of the different measurement loops in the internal resistance Ri, the dynamic measurement accuracy is different, and the unreasonable or faulty measurement operation in the field, etc. There will be differences in the measurement results of the tested product. In the actual measurement, the specificity of the insulation resistance test conditions of the loop resistance tester should be combined to minimize possible measurement errors:

(1) Different types of insulation meter When measuring the same sample, the same voltage level and wiring method should be used.

(2) Different types of loop resistance testers have different scales and indications, different scale resolutions, and different levels of measurement accuracy, which can cause differences between indications. In order to ensure the accurate measurement of power equipment, the use of low-accuracy and inconvenient rocking watches should be avoided.

(3) Most of the test samples contain capacitive components and there is dielectric polarization. Even if the test conditions are the same, it is difficult to obtain ideal data repeatability.

(4) During the measurement, the temperature of the insulating medium and the temperature of the oil should be the same as the ambient temperature, generally allowing a difference of ± 5%.

(5) The measured value should be read as soon as possible within the allowable time difference of the specific time period. In order to make the measurement error not higher than ±5%, the time allowed for reading R60S is ±3S, while the time for reading R15S should not be ±1S.

(6) When the high-voltage test power source is non-ideal, the output voltage is lower than its rated value when the load is heavy (the insulation resistance value of the tested product is small), which will lead to the measurement accuracy of the single branch direct-reading insulation resistance tester. The conversion factor changes to decrease. This change will vary depending on the load test characteristics of the insulation resistance tester.

(7) Insulation resistance tester for different dynamic test capacity indicators, the test voltage on the test sample (and on the sampling resistor) and the test sample charging capacity are different, the measurement results will be different, using less than dynamic Insulation resistance tester for measuring capacity index threshold, due to inertial network (including mechanical inertia of pointer instrument) caused by the inertia of the meter, the response speed of the indication is slow, and it is too late to correctly reflect the change rule of the actual insulation resistance of the test piece with time. In particular, in the initial stage of the test, the capacitor charging current is not completely attenuated to zero, which will cause a larger error (smaller) for R15S and absorption ratio readings.

(8) The polarization state of the dielectric of the test object is related to the magnitude of the applied test voltage. Because the test voltage can not reach the rated value quickly, or because of the difference in test voltage applied to the test sample due to the different load resistance characteristics of the insulation resistance tester, the initial polarization state of the test sample is different, resulting in different absorption current, so that the edge resistance measurement Different indications.

(9) The test high voltage of certain insulation resistance testers in foreign countries can be continuously adjusted. After starting up, it can be adjusted from zero to the rated value. The uncertainty of the starting time of the reading of the insulation resistance tester, and the uncertainty of the time the high pressure reaches the rated value, causes the initial polarization of the test sample to be different, which will also cause the difference between indication values.

(10) Different loop resistance testers have different on-site interference susceptibility and resilience, and there may be differences in the readings of the same sample.

(11) The difference between indications is caused by the difference between the normal measurement error of data random fluctuation and the method error of the insulation resistance tester.

(12) Insufficient medium discharge is one of the important reasons for the difference in repeated measurement results. According to the characteristics of the charge and absorption current of the test sample corresponding to its reverse discharge current and reversible, if the second repeated measurement of the same sample is required, the short-term discharge interval of the sample after the first measurement is generally longer than the measurement time. Deplete the amount of absorbed electric charge accumulated so that the insulating medium of the test product can be fully restored to the original state without polarization, otherwise it will affect the accuracy of the second measurement data. In order to ensure that there is no residual charge on the test object, the measurement terminal should be short-circuited to ground before every test, sometimes even taking approximately one hour, and the connection with the unrelated equipment should be removed. In short, the same test sample insulation measurement at different times, should use the same test voltage level and wiring method, and use the same type or performance of insulation resistance table as close as possible to ensure the comparability of the measurement data.

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