Application method of insulation resistance meter

The use of insulation resistance meter megger

modern life changes with each passing day, and people can't live without electricity for a moment. In the process of using electricity, there are electricity safety problems, such as motors, cables, household appliances and so on. One of their normal operation is the insulation degree of their insulating materials, that is, the value of insulation resistance. When the fake and shoddy and low-cost aluminum alloy cables on the market are heated and damp, once the components 1 of the electronic universal testing machine are damaged, it will directly affect its work, and the insulating materials will age. The insulation resistance is reduced. So as to cause electric leakage or short circuit accidents of electrical equipment. In order to avoid accidents, it is required to measure the insulation resistance of various electrical equipment frequently. Judge whether the insulation degree meets the needs of the equipment. The measurement of common resistance usually has two methods: low voltage measurement and high voltage measurement. The insulation resistance is generally high (generally megaohm level). The measured value at low voltage cannot reflect the true insulation resistance value operating at high voltage. Megger is also called insulation resistance meter. It is the most commonly used instrument for measuring insulation resistance. It has high voltage power supply when measuring insulation resistance, which is the difference between it and resistance measuring instrument. Megger is convenient and reliable for measuring insulation resistance. However, if it is not used properly, it will bring unnecessary errors to the measurement. We must correctly use the megger insulation resistance for measurement

when the megger is working, it generates high voltage, and the measuring object is electrical equipment, so it must be used correctly, otherwise it will cause personal or equipment accidents. Before use, the following preparations must be made:

(1) before measurement, the power supply of the tested equipment must be cut off and discharged in a short circuit to the ground. The equipment must not be charged for measurement to ensure the safety of personnel and equipment. (2) For the equipment that may induce high-voltage electricity, it must be used as the oil filling valve or oil drain valve of the hydraulic system of the cement constant stress pressure testing machine after eliminating this possibility; It can be measured only when it is connected in series with the pressure valve. (3) The surface of the measured object shall be clean to reduce the contact resistance and ensure the correctness of the measurement results. (4) Before measurement, check whether the megger is in normal working condition, mainly check its "0" and "∞" points. That is, shake the handle to make the motor reach the rated speed. The megger should point to the "0" position in case of short circuit and the "∞" position in case of open circuit. (5) The megger shall be placed in a stable and firm place and away from large external current conductor and external magnetic field

after the above preparations are made, the measurement can be carried out. During the measurement, pay attention to the correct wiring of the megger, otherwise unnecessary errors or even errors will be caused. There are three terminals of vortex flowmeter

megger: one is "L", which is the line end, one is "e", which is the ground end, and the other is "g", which is the shielding end (also known as the protective ring). Generally, the measured insulation resistance is connected between "L" and "e", but when the surface of the measured insulator leaks seriously, the shielding ring or the part that does not need to be measured must be connected with the "g" end. In this way, the leakage current directly flows back to the negative end of the generator through the shielding end "g" to form a loop, instead of flowing through the measuring mechanism (moving coil) of the megger. In this way, the influence of surface leakage current is fundamentally eliminated. In particular, it should be noted that when measuring the insulation resistance between the cable core and the outer surface, the shielding terminal button "g" must be connected, because when the air humidity is high or the cable insulation surface is not clean, the leakage current on the surface will be very large. In order to prevent the influence of the measured object on its internal insulation measurement due to leakage, a metal shielding ring is generally added on the outer surface of the cable, Connected to the "g" end of the megger

when megger is used to measure the insulation resistance of electrical equipment, it must be noted that "L" and "e" terminals cannot be connected reversely. The correct connection method is: "L" line terminal button is connected to the conductor of the tested equipment, "e" grounding terminal button is connected to the equipment shell, "g" shielding terminal is connected to the insulation part of the tested equipment. If "L" and "e" are connected reversely, the leakage current flowing through the insulation body and surface will flow through the shell to the ground, and then flow into the measuring coil through "L", so that "g" will lose its shielding effect and bring great error to the measurement. In addition, because the insulation between the internal lead of the "e" end and the shell is lower than that between the "L" end and the shell, when the megger is used on the ground and the correct wiring method is adopted, the insulation resistance of the "e" end to the instrument shell and the shell to the ground is equivalent to a short circuit and will not cause error. When the "L" and "e" are inversely connected, the insulation resistance of the "e" to the ground is connected in parallel with the measured insulation resistance, resulting in a small measurement result, Bring large error to the measurement