How to Measure Insulation Resistance Correctly Using a Megaohmmeter

How to use Megohmmeter correctly Measure insulation resistance Measure the insulation resistance with a megohmmeter. Pay attention to the following points:

(1) Before testing, remove the resistance of the tested power cable and all outbound wires, ground them and discharge them. The discharge time should not be less than 1min, and the power cables with larger capacity should not be less than 2min to ensure safety and accurate test results. .

(b) Use a dry, clean, soft, soft cloth to remove dirt from the end caps or wires and the insulation surfaces of power cables to reduce surface leakage.

(3) Place the oscillating table in a stable horizontal position to avoid unsteady shaking of the table during operation, resulting in inaccurate readings.

(d) Under no-load conditions, rotate the oscillating table to the rated speed (120 r/min) and adjust the pointer to "∞".

(v) For multi-core power cables, the insulation resistance of each phase core should be tested separately. At this time, the lead wire to be tested is connected to the connection terminal (L) of the oscillating meter, and the other core wire is shorted to the ground (lead packet) and then connected to the grounding terminal (E) of the oscillating meter. In order to avoid the influence of the leakage current on the insulation surface of the power cable, a rocking screen should be used to knock the wall (G) to fully break the surface insulation beyond the instructions of the rocking table. For power cables that have not yet been laid, install a protection ring around the insulation of the core of the core to be tested, and connect the two protection rings to the shield terminals (G) of the oscillating meter, as shown in Figure 8-2. For the already installed power cable, a metal soft wire can be used to wrap the protection ring on the sleeve or insulation at both ends of the core to be tested, and the protection rings at both ends can be connected to the rocking shielding terminal, and another power cable can be used. The core acts as a shielded loop, as shown in Figure 8-3.

(f) Rotate the rocker handle at a constant speed (at 120r/min, the pointer gradually rises, record the insulation resistance value after 1min. The reason for this is that considering that there are three kinds of insulation decay with time. The current, in theory, should be such that after all three currents have been attenuated, the value of the conducting current (ie, the leakage current) is read out to calculate the insulation resistance, but due to the long time, the workload of the section test is large and the test is taken into consideration. Because of the stability of the system, it is clearly stated in the standards of the test method that the readings are reaching one minute after the current is switched on.This provision ensures that most of the non-conducting currents have disappeared and the test time has been unified. , Make the readings repeatable and comparable, while improving the test efficiency.

(7) When the insulation of the power cable is also obstructed or measurement is required, the power cable under test must be grounded and discharged for at least two minutes.

(h) Since the insulation of the power cable line is also affected by many external conditions, it is important to fill in the inscription or table plum in the test to facilitate the analysis of the test results.

It should also be pointed out that the insulation resistance of the L-lead wire of the oscillating meter is in parallel with the insulation resistance of the power cable, so the insulation resistance of the wire is required to be high, and should not be dragged on the ground, and should not be connected with the E-terminal lead, such as When the leads must be connected via other supports and power cable cores, the support must be well insulated or it will affect the accuracy of the measurement. In the test process, the speed of the oscillating table should be kept as much as possible and the uniform speed should be maintained. The speed of rotation should not be less than 80% of the speed of the front stern.

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