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Detection Technology

Megger to measure cable insulation resistance

time:2020/8/19   source:华天电力  reading:526 time

Check before measurement:

When the megohmmeter is not connected to any wires or objects, shake the handle to the rated speed, check whether the pointer is in the "∞" position, and then talk about another line L, ground E. Shorten the terminal and slowly rotate the generator handle. Check whether the pointer points to "0". If the pointer cannot be pointed or "∞" is "0", it means that the search is wrong, the correct measurement result cannot be obtained, and it must be stopped.

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Megger wiring:

A megohmmeter usually has three terminals, one is a terminal, marked as L, one is a ground terminal, marked as E, and the other is a protective or shielding terminal, marked as G. When measuring, L and the measuring device are connected to Ground the insulated conductor part, and connect E to the case or other conductor part of the device under test. When measuring, usually only the two terminals of L and E can be used. However, when the surface of the device under test is severely leaked, it will have a great impact on the measurement result and is difficult to eliminate. For example, the air is too humid. , When the surface of the insulating material is etched and cannot be cleaned, the G terminal must be connected. In this way, the surface leakage current starts from the positive pole of the generator and flows back to the negative pole of the generator through terminal G, forming a loop and no longer passes through the measuring mechanism of the megohmmeter, thereby eliminating the influence of surface leakage current on the measurement.

Measurement and reading:

The use of the meridian should be laid flat so as not to affect the free rotation of the measuring mechanism. When shaking the handle, it should be slow and fast, accelerate evenly and stabilize to 120r/min. Do not flicker and slow, otherwise the pointer will swing back and forth and the correct reading will not be read. During the shaking process, when the pointer points to 0, if the coil in the watch is damaged, it will no longer continue to shake. Due to the insulation resistance of the device under test, according to the length of the measurement time, it is usually used after a constant speed of 1 minute. When the pointer is stable, it can be read and recorded. When necessary, record the ambient temperature and climatic conditions during the measurement, as well as the voltage level of the megohmmeter used, the measurement range and the condition of the device under test for comprehensive analysis.

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