Megausi Table is commonly known as a shaker. It is a portable instrument that is designed to detect electrical equipment and supply line insulation resistance. The electrical equipment is good and the insulation performance is related to the normal operation of the electrical equipment and the personal safety of the operator. In order to prevent damage caused by heat generation, moisture, contamination, aging, etc. due to heat, lacking, contamination, aging, and requires frequently measured insulation resistances in order to inspect the insulation performance after repair.
Why can't the insulation resistor can measure the ohm gear milling of a multimeter? Because the resistance of the insulation resistance is relatively large, it is often more than tens of MΩ or more, the power supply voltage at the time of measuring the resistor is very low (9V below), the resistance presented under low voltage The value does not reflect the true value of the insulation resistance under high voltage. Therefore, the insulation resistance must be measured using a megapherometer with high voltage power supply.
Megou Table When working, it produces high voltages, and the measurement object is electrical equipment, so it must be used correctly, otherwise it will cause personal or equipment accidents. This article summarizes some methods for proper use and maintenance for your reference.
I. Structure and Selection of Megaus
It consists of a hand generator, a header, and a three-terminal (i.e., L: line end, E: ground end, G: shield end), "G" (ie, the shielded end) is also a protective ring.
The choice of rated voltage level: high-voltage electrical equipment insulating resistance requirements are high, and it is necessary to use a megaphuri table for high voltage. The voltage can be subsequently capable of withstand the internal insulating material within low-voltage electrical equipment. In order to ensure the safety of equipment, it should select a low voltage. European table. Under normal circumstances, the equipment of the rated voltage is below 500 V shall be used with 500V or 1000VEE: The rated voltage is 500V or more, and the megapherus table is selected from 1000V ~ 2500V.
Selection of resistance measurement range: Selecting the principle of mega Europe is not to prevent the measurement range too much to exceed the value of the insulated resistance, so as not to produce a large read error due to the thickness of the scale. In addition, pay attention to some mega Table's starting scale is not zero, but 1mΩ or 2mΩ. This mega Table should not measure the insulation resistance of low-voltage electrical equipment in a humid environment, because the equipment insulation resistance in this environment is small, it is possible to less than 1mΩ, and reading is not read on the meter. Easy to mistakenly believe that the insulation resistance is 1mΩ or zero value. There are two small black dots on the dial scale line of the megaus table, and the area between the small black spots is the accurate measurement area. Therefore, the insulation resistance value of the device under test should be made in the accurate measurement area when selecting the table.
Second, the correct usage method of megohmmeter
1 Before the measurement, the measured device must be cut off and short circuit is discharged. Never make the equipment to measure to ensure the safety of personal and equipment. Measurement must be performed after the device that may induce high piezoelectric power is eliminated.
2 is cleaned on the surface of the test. Reduce contact resistance to ensure the correctness of the measurement results.
3 The megapherd table should be opened and short-circuit test before measurement, and it is good to check if Zhaobi is good. That is, before the SMU did not connect to the measured object. The shake handle allows the generator to reach the rated speed (120R / min), and observe whether the pointer refers to the "∞" position in the scale. The terminal "line (L) and the ground (E)" are short, and the handle is slowly shaken, and the pointer refers to the "0" bit in the scale. If the pointer cannot be referred to as the point of the finger, it indicates that the mega Table has faults. It should be used after repair.
4 MegM Table should be placed in a smooth, secure place, and away from large external current conductors and magnetic fields.
5 must be wired correctly. There are generally three terminals on the megoh form, where l is connected to the body portion of the measured object and the mainland insulation, E-attached housing or earth. G is connected to the shield of the subject or does not require the measured portion. When the insulation resistor is measured, only "L" and "E" are generally used. However, when measuring the insulation resistance of the cable or the leakage current of the measured device is more serious, the "G" end is used, and the "G" ends the shield or housing. After the line is connected, you can turn the shake in a clockwise direction. The speed of shaking should be slow, when the speed reaches about 120 revolutions per minute (ZC-25), keeps moving at a constant speed, 1 minute after reading. And you are looking at the side reading. Can't stop reading.
Note: When the insulation resistance of the electrical device is shaken with a mega, it must pay attention to the "L" and "E" ends cannot be reversed. The correct connection is: "L" line end button is connected to the device cover of the device conductor, "E" ground button. "G" shields the insulation portion of the ended measurement device. If "L" and "E" are reversed, the leakage current flowing through the insulation and the surface is collected from the housing. The measuring coil flows from the ground "L". Make "G" lose shielding effects to bring great errors to measurements. In addition, since the internal lead in the "E" end is lower than the insulation of the outer casing than the "L" end and the insulation of the outer casing. When the Mega Table is placed on the ground, when the correct wiring is used, the "E" ends the insulation resistance of the instrument housing and the outer casing, which is equivalent to the short circuit, and does not cause errors, and when "L" is connected to "E" Time. "E" is parallel with the insulation resistance of the ground to the ground. The measurement results are small and larger errors are given to measurements.
6 When the test is placed in the horizontal position, and the steering is not short-circuited when the rotation is turned. The shaking handle should be slowly faster, and if it is found that the pointer refers to the instructions may have a short circuit, then the handle cannot be shaken. To prevent heat damage of the inner coil.
7 The reading is completed. Discharge the device under test. The discharge method is to take the measurement from the megoh in the megaphoe, and the device is shorted (not a megaphoe discharge).
Third, the precautions in the measurement
1. It is forbidden to test the insulating resistance near lightning or the high pressure equipment, and can only be charged in the device. There is also no inductive electricity.
2. During the test. Some people can't work on the device under test.
3. Mega Waters cannot be stranded together. To separate.
4. The Megou Form did not stop rotation or before the device was not discharged. It is struggled to use his hand. Do not touch the metal portion of the lead in the wire.
5. At the end of the measurement. For large capacitive equipment to discharge.
6. The measurement cord of megaus terminal leaders should be good, and the two wires and the ground should be properly distance to avoid affecting the measurement accuracy.
7. In order to prevent the surface of the test device from leakage resistance, it is used as a mega. The intermediate layer of the device under test (such as the inner insulator between the cable casing core) is connected to the protection ring.
8. To verify its accuracy.
Author: Zhang Liang
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