Electronic insulation megohmmeter use method - Database & Sql Blog Articles

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(1) Preparation before use

(1) Before the measurement, the power of the device under test must be cut off, and the ground should be short-circuited. The device must not be energized for measurement to ensure the safety of the person and equipment.

(2) For equipment that may induce high voltage, the possibility must be eliminated before measurement can be made.

(3) The surface of the object to be tested should be cleaned to reduce the contact resistance and ensure the correctness of the measurement results.

(4) Before the measurement, check whether the digital megohmmeter is in normal working condition, mainly check the two points of “0” and “∞”. That is, the handle is shaken to make the motor reach the rated speed. The digital megger should be in the “0” position when it is short-circuited and “∞” when it is open.

(5) The digital megger should be placed in a stable and stable place away from large external current conductors and external magnetic fields.

(2) Correct use

There are three terminals for digital megohmmeter: one is “L”, that is, the line end, one “E” is the ground end, and another “G” is the shield end (also called the protection ring), The measured insulation resistance is connected between the “L” and “E” terminals. However, when the surface of the tested insulator is seriously leaky, the shield ring of the test object or the part not to be measured must be connected to the “G” end. In this way, the leakage current flows directly back to the negative end of the generator via the shield end "G" to form a loop, rather than flowing through the measuring mechanism (moving coil) of the digital megohmmeter. This fundamentally eliminates the influence of surface leakage current. In particular, it should be noted that when measuring the insulation resistance between the cable core and the outer surface, the shield terminal "G" must be connected because the air humidity is high or the cable is insulated. When the surface is not clean, the leakage current on the surface will be very large. In order to prevent the measured object from being affected by leakage, its internal insulation measurement is generally added to the outer surface of the cable with a metal shielding ring, and the digital megohmmeter. The G" ends are connected.

When using a digital megohmmeter to measure the insulation resistance of electrical equipment, be sure to note that the "L" and "E" ends cannot be reversed. The correct connection is: "L" line end button is connected to the conductor of the device under test, "E The grounding device is grounded, and the “G” shield terminates the insulated part of the device under test. If the "L" and "E" are reversed, the leakage current flowing through the insulator and the surface is collected to the ground through the outer casing, and the ground flows through the "L" into the measuring coil, so that the "G" loses the shielding effect and gives the measuring tape. There is a big error. In addition, because the inner lead of the "E" end is insulated from the outer casing by a lower degree than the "L" end and the outer casing, when the digital megohmmeter is placed on the ground, the "E" end is used when the correct wiring is used. The insulation resistance of the outer casing and the outer casing to the ground is equivalent to a short circuit and does not cause an error. When "L" and "E" are reversed, the insulation resistance of the "E" to the ground is in parallel with the measured insulation resistance, and the measurement result is obtained. Smaller, causing large errors in the measurement.