- Operating principle of
- Operating Instructions
- Video Tutorials
Operating principle of
The megaohmmeter generates a voltage by its own high-voltage converter, and milliammeter registers the current in the measured circuit. From the school course of physics, we know Ohm's law, and the connection between the resistance R, which is equal to U divided by I.
Currently, the digital measuring instruments are distributed because of their compactness and lightness, but hand-held models with manualdynamo-machine. Now we will consider how to correctly use the megaohmmeter of the old model and the new one.
We draw your attention to the fact that some people call a device for measuring the insulation resistance of a megohmmeter. This is not quite the right name, becauseif the word is broken in parts, we get the prefix "mega", the unit of measurement is "Om" and "meter"( from Greek it is translated as a measure).
Operating Instructions
Insulation resistance check is performed on de-energized equipment or cable line, wiring. Remember that the device generates a high voltage and if security measures are violated using a megger, electro-injury is possible, becauseMeasuring the insulation of a capacitor or a long-distance cable line can result in the accumulation of a dangerous charge. Therefore, the test is carried out by a team of two people who have an idea of the danger of electric current and have received a tolerance for TB.During the test of the object, there should not be any strangers near by. Remember the high voltage.
The device is inspected for integrity at each use, for the absence of chips and damaged insulation on the probes. A trial test is carried out by testing with diluted probes and closed ones. If the tests are performed by a mechanical device, then it should be placed on a horizontal level surface, so that there is no error in the measurements. When measuring the insulation resistance with a mega-meter of the old sample, it is necessary to rotate the generator handle at a constant frequency, approximately 120-140 rpm.
If you measure resistance against the body or ground, two probes are used. When testing the conductors of the cable relative to each other, use the "E" megger and the cable shield to compensate for the leakage currents.
Insulation resistance is not a constant value and largely depends on external factors, so it can vary during the measurement. The test is performed for a minimum of 60 seconds, starting from 15 seconds the readings are recorded.
For household networks, tests are performed with a voltage of 500 volts. Industrial networks and devices are tested with a voltage in the range of 1000-2000 volts. It is necessary to find out the exact measuring range in the operating instructions. The minimum allowable resistance for networks up to 1000 volts is 0.5 MΩ.For industrial devices, not less than 1 MΩ.
As for the measurement technology itself, use a megaohmmeter as described below. For example, we took the situation with the measurement of insulation in the SSR( power shield).So, the procedure is as follows:
- We lead people out of the verified part of the electrical installation. We warn of danger, post warning posters.
- Remove the voltage, de-energize the entire shield, the lead-in cable, take measures against the erroneous supply of voltage. Post a poster - DO NOT TURN ON, PEOPLE WORK.
- Check the absence of voltage. Preliminary grounding of the terminals of the object under test, we install test probes, as shown in the connection diagram of the megaohmometer, and also we remove the grounding. This procedure is carried out with each new measurement, as nearby elements can accumulate charge, introduce an error in the readings and pose a danger to life. Installation and removal of styli is made for insulated handles in rubber gloves. We draw your attention to the fact that the insulating layer of the cable must be cleaned of dust and dirt before checking the resistance.
- We check the insulation of the input cable between the phases AB, B-C, CA, A-PEN, B-PEN, C-PEN.The results are recorded in the measurement report.
- Disable all machines, RCDs, turn off the lamps and lighting fixtures, disconnect the zero wires from the zero terminal.
- We measure each line between phase and N, phase and PE, N and PE.The results are entered in the measurement protocol.
- In case of defect detection, we disassemble the measured part into its component parts, search for the fault and eliminate it.
After the test with portable grounding, we remove the residual charge from the object, by short-circuiting, and the measuring device itself, discharging the probes with each other. Here, according to this instruction, it is necessary to use a megaohmmeter when measuring insulation resistance of cable and other lines. To help you understand the information, below we provided a video, which clearly demonstrates the order of measurements when working with certain models of devices.
Video Tutorials
First of all, we bring to your attention the instruction manual for the switch megawatt ECO202 / 2-G:
Another popular point meter, which is an analogue of the above model - m4100.It's also quite easy to use, as you can see by watching this video:
Digital megameters with a display are even easier to use. For example, it is possible to measure the insulation resistance of a cable with a modern UT512 UNI-T meter using the following technology:
The last instruction also deals with another popular device - E6-32.The video below shows in some detail how to use a megaohmmeter to measure the insulation resistance of a transformer, a cable, or even a metal link:
This is how the insulation resistance is measured with a megaohmmeter. As you can see, this device is not difficult to use, but you need to take safety seriously and take all the necessary measures for protection.
It will be interesting to read:
- How to measure the resistance of a tester with a tester
- How to correctly use the multimeter
- How to test the operation of the transistor
