To measure insulation resistance using a megohmmeter - Solutions - Huaqiang

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To measure the insulation resistance using a megger, pay attention to the following points:
(1) Before the test, remove the resistance of the tested power cable and all external wiring, and discharge it to the ground. The discharge time shall not be less than 1 min, and the power cable with large capacitance shall not be less than 2 min to ensure safety and accurate test results. .
(2) Wipe off the dirt on the power cable terminal sleeve or core wire and its insulating surface with a dry, clean soft soft cloth to reduce surface leakage.
(3) Place the shaker in a stable horizontal position to avoid shaking the watch during uneven operation, resulting in inaccurate readings.
(4) Under no-load condition, turn the shaker handle to the rated speed (120r/min) and adjust the pointer to “∞”.
(5) For multi-core power cables, the insulation resistance of each phase core wire shall be tested separately. At this time, connect the measured core lead wire to the terminal (L) of the shake table, short the other core wire to the ground (lead pack) and connect it to the ground terminal (E) of the shake table. In order to avoid the influence of leakage current on the insulation surface of the power cable, the wall should be knocked against the wall (G) with a shake-down screen to completely knock the surface insulation out of the indication of the shake table.
(6) Rotate the table handle at a constant speed (when 120r/min, its pointer gradually rises, after 1min, record its insulation resistance value. The reason for this is because there are three kinds of attenuation in time due to the insulation. The current, in theory, should wait until the three currents are all attenuated before reading the value of the conduction current (ie, leakage current) to calculate the insulation resistance. However, because the time is too long, the amount of work is large and the test is considered. The stability of the system time, so it is clearly stated in the standard of the test method that the reading is reached after one minute is reached after the current is turned on. This regulation not only ensures that most of the non-conductive current has disappeared, but also makes the test time uniform. , making readings repeatable and comparable, while improving test efficiency.
(7) When the insulation of the power cable is also blocked or needs to be repeatedly measured, the power cable of the test must be grounded and discharged for at least two minutes.
(8) Since the insulation of the power cable line is also affected by many external conditions, the record or meter should be carefully filled in the test to facilitate analysis of the test results.
It should also be pointed out that the insulation resistance of the L-terminal lead of the shaker is parallel with the insulation resistance of the power cable, so the insulation resistance of the lead is required to be high, and should not be dragged to the ground, and should not be tied with the E-terminal lead, such as When the lead must be connected to other supports and the power cable core, the support must be well insulated, otherwise the measurement accuracy will be affected. During the test, the speed of the shaker should be kept as high as possible and maintain a uniform speed. The speed of the swing should not be less than 80% of the front speed.