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(1) Before measurement, the power supply of the device under test must be cut off, and the device should be short-circuited and discharged to ground. It is absolutely forbidden to measure with the device energized, to ensure the safety of personnel and equipment.

(2) For equipment that may induce high voltage, measurement can only be carried out after eliminating this possibility.

(3) The surface of the object under test should be clean to reduce contact resistance and ensure the accuracy of measurement results.

(4) Before measurement, check whether the high voltage insulation resistance tester is in normal working condition, mainly checking its "0" and "∞" points. That is, shake the handle to make the motor reach rated speed. When short-circuited, the megger should point to "0"; when open-circuited, it should point to "∞".

(5) The high voltage insulation resistance tester should be placed on a stable and firm surface, away from large external current conductors and external magnetic fields.

    After completing the above preparatory work, measurement can be carried out. During measurement, attention should also be paid to the correct wiring of the high voltage insulation resistance tester, otherwise unnecessary errors or even mistakes may occur. Vortex flowmeter

    High voltage insulation resistance tester has three terminals: one is "L" (line terminal), one is "E" (earth terminal), and the other is "G" (guard terminal, also called guard ring). Generally, the insulation resistance under test is connected between "L" and "E". However, when surface leakage of the insulation under test is severe, the guard ring of the object under test or the part not requiring measurement must be connected to the "G" terminal. In this way, leakage current flows directly back to the negative terminal of the generator through the guard terminal "G" to form a loop, without flowing through the measuring mechanism (moving coil) of the megger. This fundamentally eliminates the influence of surface leakage current. Special attention should be paid when measuring the insulation resistance between the cable core and its outer sheath: the guard terminal "G" must be properly connected, because when air humidity is high or the cable insulation surface is not clean, the surface leakage current will be large. To prevent the influence of leakage on the internal insulation measurement, a metal guard ring is generally added to the cable outer sheath and connected to the "G" terminal of the megger.

    When using a megger to measure the insulation resistance of electrical equipment, it is important not to reverse the "L" and "E" terminals. The correct connection is: "L" line terminal connected to the conductor of the device under test, "E" earth terminal connected to the grounded equipment casing, and "G" guard terminal connected to the insulating part of the device under test. If "L" and "E" are reversed, the leakage current flowing through the insulation and its surface will be collected by the casing and flow to ground, then from ground through "L" into the measuring coil, causing "G" to lose its shielding effect and introducing significant errors. Additionally, because the insulation level between the internal lead of the "E" terminal and the casing is lower than that between the "L" terminal and the casing, when the megger is used on the ground with correct wiring, the insulation resistance between "E" and the instrument casing and between the casing and ground is effectively short-circuited, causing no error. However, when "L" and "E" are reversed, the insulation resistance between "E" and ground is in parallel with the measured insulation resistance, resulting in a lower measurement value and introducing significant errors.







Note: The above information and technical parameters are compiled and released by Yangzhou Darui Electric Co., Ltd.