Problems encountered in the measurement of digital ohmmeter
In the detection of insulation, the insulation resistance of a time value is not fully reflect the insulation performance of the sample, this is due to the following two reasons, on the one hand, the same insulation material, has large volume when the insulation resistance is small, the volume of the insulation resistance in hours. On the other hand, there is a charge absorption process and polarization process for the insulating material after the addition of high pressure. Therefore, the requirements for power system in main transformer, cable, motor and so on many occasions in the insulation test should measure the absorbance ratio R60s and R15s ratio, and polarization index - R10min and R1min ratio, and uses these data to determine insulation.
When measuring the capacitive load resistance, what is the relation between the magnitude of the short-circuit current and the measurement data?The magnitude of the short circuit current produced by the ohmmeter can reflect the magnitude of the internal impedance of the high voltage source output. When a capacitor is detected, the high voltage source in the ohmmeter charges the capacitor through its internal resistance at the beginning of the detection process, and gradually charges the voltage to the output rating voltage of the ohmmeter. Obviously, if the capacitance of the sample is very high, or the internal resistance of the high voltage source is very large, the charging process will be time-consuming. Its length can be determined by the product of the R and the C load (in seconds). Note that the current charged to the capacitor and the current flowing through the insulation resistance of the detected product are flowing together in the test. The current measured by the ohmmeter not only has the component of the insulation resistance, but also has a capacitive charging current component, and the measured resistance will be smaller at this time.
A, please follow the wiring diagram of measurement, can you identify all the insulation detection the measuring results are accurate: when the measurement time of 15 seconds, the instrument display should be R15s > 4750 M ohm (due to capacitor C, so the measured value than the nominal value of 5%); when measuring time 60 seconds, the instrument display should be R60s=5000M, the absorption ratio should be less than 1.05 R60s/R15s. Fifteenth seconds, the instrument charge to the capacitive C current is smaller, indicating that the more powerful the instrument charge, the absorption ratio tends to "1"". The right in the absorption field detection of bizet.
