Insulation resistance tester is suitable for measuring the resistance value of various insulation materials and the insulation resistance of transformers, motors, cables and electrical equipment to ensure that these devices, electrical appliances and circuits work in a normal state, to avoid accidents such as electric shock and death and equipment damage. In order to make everyone use the instrument better, here are some common questions in the measurement process.
1. What is the relationship between the output short-circuit current of the insulation resistance tester and the measured data when measuring the capacitive load resistance?
The magnitude of the output short-circuit current of the edge resistance tester can reflect the internal resistance of the internal high-voltage source output of the megohmmeter. When the tested product has capacitance, at the beginning of the test process, the high voltage source in the insulation resistance tester must charge the capacitor through its internal resistance, and gradually charge the voltage to the rated high voltage value of the insulation resistance tester. Obviously, if the capacitance of the test sample is very large, or the internal resistance of the high voltage source is large, the charging process will take longer. Its length can be determined by the product of R inner and C load (in seconds). Please note that the current flowing to the capacitor and the current flowing through the insulation resistance of the product under test will flow into the insulation resistance tester. The current measured by the insulation resistance tester not only has a component in the insulation resistance but also a capacitor charge current component, and the measured resistance will be small.
2. When measuring insulation, it is not only required to measure the simple resistance, but also to measure the absorption ratio and polarization index. What is the significance?
In the insulation test, the insulation resistance value at a certain moment cannot fully reflect the good or bad of the insulation performance of the test product. This is due to the following two reasons. On the one hand, the insulating material with the same performance has small insulation resistance when the volume is large. , The volume of the insulation resistance is small. On the other hand, the insulating material has a charge-absorption ratio process and a polarization process after applying a high voltage. Therefore, the power system requires that the absorption ratio, that is, the ratio of R60s and R15s, and the polarization index, that is, the ratio between R10min and R1min, should be measured in insulation tests of main transformers, cables, and motors, etc., and the data is used to determine the insulation status. The pros and cons.
3. In the high-pressure and high-resistance test environment, why do I need to connect the "G" terminal to the instrument?
When the rated voltage is high at both ends of the test object, and the insulation resistance is high, the surface of the tested product is exposed to moisture, and the leakage caused by the pollution is large. The indication error is large, and the “G†terminal of the instrument is The current leakage from the surface of the test object is bypassed so that the leakage current does not pass through the test circuit of the meter and the error caused by the leakage current is eliminated.
4. When measuring the rated output DC high voltage of certain types of insulation instruments "L" and "E" at both ends, measure the L and E voltages with the analog multimeter DCV, why the voltage will drop a lot, and the digital multimeter is will not?
Measure the rated DC voltage directly at both ends of the insulation resistance tester "L" and "E" with an ordinary analog multimeter, and the measurement result is much smaller than the nominal rated voltage (out of the error range), and use the number The multimeter will not. This is because the pointer type multimeter has a smaller internal resistance, and the digital multimeter has a relatively large internal resistance. The pointer multimeter has a smaller internal resistance, and the output voltage of the insulation resistance tester LE decreases much, and is not the output voltage during normal operation. However, using a multimeter to directly measure the output voltage of the insulation resistance tester is wrong, and it should be measured with a static high voltage meter with a large internal resistance or with a load voltage resistance such as a voltage divider.
5. Why does the electronic insulation resistance tester generate a high DC voltage when several battery power supplies are used?
This is based on the principle of DC conversion. After the boost circuit processing, the lower supply voltage is raised to a higher output DC voltage. Although the generated high voltage is high, the output power is small.
The above are some of the problems we have encountered in measuring the insulation resistance using the insulation resistance tester . Understanding it and understanding it are very beneficial to our testing work.
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