Megger

1、 Introduction




Megger is a kind of measuring instrument commonly used by electricians. It is mainly used to check the insulation resistance of electrical equipment, household appliances or electrical lines to the ground and between phases, so as to ensure that these equipment, appliances and lines work in a normal state and avoid accidents such as electric shock casualties and equipment damage. The scale of the megohmmeter is in megaohm (m Ω). The megohmmeter is composed of medium and large scale integrated circuits. This meter has high output power, high short-circuit current value and many output voltage levels (each model has four voltage levels). Megohmmeter is a common and necessary instrument for electric power, post and telecommunications, communication, mechanical and electrical installation and maintenance, as well as the industrial enterprises and departments using electric power as industrial power or energy. It is suitable for measuring the resistance of various insulating materials and the insulation resistance of transformers, motors, cables and electrical equipment.




2、 Nickname



Digital megger, pointer megger, insulation meter, high-voltage insulation resistance tester, insulation resistance tester, insulation characteristic tester, electromotor, electronic insulation resistance tester, high-power high-voltage megger, megger, digital megger, digital display megger, insulation resistance tester, high-voltage insulation resistance tester, insulation resistance tester, insulation characteristic test Instrument, electric megger, digital megger, digital megger, digital megger, high voltage digital insulation resistance tester, digital high voltage insulation resistance tester, digital high voltage megger, digital high voltage megger, high voltage digital megger, digital insulation meter, digital insulation meter, electronic insulation resistance tester, digital insulation resistance tester, digital insulation resistance test instrument Digital insulation resistance tester, insulation resistance tester, digital megger insulation resistance meter, digital electric megger, digital high voltage megger, high power high voltage megger.




3、 Basic parameters



（1） Voltage test

DC 25, 501002505001000v



（2） Measuring range

25-50v: 2m Ω ~ 200m Ω, 3-gear range

100-250V: 2m Ω ~ 2000m Ω, 4-gear range

500-1000v: 2m Ω ~ 4000m Ω, 4-gear range



（3） Accuracy

±2%rdg. ±5dgt.



Test voltage of 25 ~ 100V: 0 ~ 20.00m Ω



250V test voltage: 0 ~ 100.0m Ω



Test voltage of 500 ~ 1000V: 0 ~ 999m Ω



±5%rdg.



Test voltage of 25 ~ 50V: 19.0 ~ 200.0m Ω



Test voltage of 100V: 19.0 ~ 2000m Ω



Test voltage of 250: 100.1 ～ 2000m Ω



Test voltage of 500 ~ 1000V: 1000 ~ 4000m Ω




（4） Response time

Fast speed: less than 0.7 seconds, slow speed: less than 1.5 seconds (under manual range)



（5） Sampling rate

Fast speed: 10 times / second, slow speed: 1 time / second



（6） Function

Comparison function: judge pass or fail

Test timing function: 0.5 ~ 99 seconds

Time delay and timing function: 0.1 ~ 99 seconds



（7） Power supply

100～240V AC，（50/60Hz）



（8） Volume and weight

215 w × 61 h × 213 mm, 1.1kg



（9） Annex

Power cord (1)





4、 How it works



Digital megohmmeter is composed of medium and large scale integrated circuits. This meter has high output power, high short-circuit current value and many output voltage levels (there are four voltage levels). The working principle is that the DC high voltage generated by DC / DC conversion is generated by the battery in the machine as the power supply, and then the DC high voltage is sent from the e pole to the L pole through the tested object, thus a current from the e to the L pole is generated. After I / V transformation, the calculation is completed by the divider, and the measured insulation resistance value is directly displayed by the LCD.




5、 Features



1. High output power, strong load capacity and strong anti-interference ability.

2. The case of the meter is made of high strength aluminum alloy, and equipotential protection ring and fourth-order active low-pass filter are set in the machine, which can effectively shield the external power frequency and strong electromagnetic field. As the output short-circuit current is greater than 1.6 Ma, it is easy to make the test voltage rise rapidly to the rated value of output voltage. For low resistance measurement, the voltage drop does not affect the measurement accuracy because of the proportional design.

3. It is powered by battery without manual work, and the range can be changed automatically. The panel operation and LCD display make the measurement very convenient and fast.

4. The output short-circuit current of this meter can be measured directly without load measurement.

6、 Instrument introduction -- synthetic resistance



The method of synthesizing resistor is excluded because of the limitation of design cost and size. It adopts the method of separating high-voltage resistor matrix to form an array, which can output more than 500000 resistance values. In this calibrator, there are eight ranges of resistance values, covering the range of 10 K Ω to 10 g Ω, and each range can provide 4.5-bit stable output.



Collecting the right high voltage resistor and integrating it into an instrument presents another challenge. This is the safety standard challenge related to the low voltage directive, a mandatory requirement of EU CE certification. The standard related to instrument manufacturers is en 61010 - Safety requirements for electrical equipment for measurement, control and laboratory use.




The RMS command requires a voltage limit of 1000 to be calibrated. So how to calibrate the megohmmeter with test voltage up to 5 kV? This type of instrument has a wider dynamic range, can measure resistance as high as 10 t Ω, and provides protection terminals as described above, so that it can accurately measure very high resistance values. Fortunately, such a protection configuration can form a resistance multiplier itself, effectively multiplying a known resistance to 1000 times. Equally important, since the multiplier is a discrete, isolated, independent device that can meet the high voltage required by the multiplier, it is no longer within the scope of the low voltage directive.




7、 How to choose



It is stipulated that the voltage level of the megohmmeter should be higher than the insulation voltage level of the tested object. Therefore, when measuring the insulation resistance of equipment or lines with rated voltage below 500V, 500V or 1000V megger can be selected; when measuring the insulation resistance of equipment or line with rated voltage above 500V, 1000 ~ 2500V megger should be selected; when measuring insulator, 2500 ~ 5000v megger should be selected. In general, the megger with the range of 0 ~ 200m Ω can be used to measure the insulation resistance of low-voltage electrical equipment.




8、 How to use it



1. Before measurement, the power supply of the equipment under test must be cut off and short-circuit discharge to the ground. Never let the equipment live for measurement, so as to ensure the safety of personnel and equipment. For equipment that may induce high voltage, the possibility must be eliminated before measurement.

2. The surface of the object to be measured should be clean, reduce the contact resistance, and ensure the correctness of the measurement results.

3. Before measurement, open circuit and short circuit test shall be conducted to check whether the megger is in good condition. That is, before the megger is connected to the measured object, shake the handle to make the generator reach the rated speed (120r / min), and observe whether the pointer points to the "∞" position of the scale. Short circuit the terminal "line (L) and ground (E)" and slowly shake the handle to observe whether the pointer points to the "0" position of the scale. If the pointer can not point to the position, it indicates that the megohmmeter is faulty. It should be reused after maintenance.

4. The megohmmeter should be placed in a stable and firm place, and away from large external current conductor and external magnetic field.

5. The wiring must be correct. Generally, there are three terminals on the megohmmeter, in which l is connected to the conductor part of the insulation between the measured object and the earth, and E is connected to the shell or ground of the measured object. G is connected to the shield of the measured object or the part that does not need to be measured. Generally, only "L" and "e" terminals are used to measure insulation resistance. However, when the insulation resistance of cable to ground or leakage current of equipment under test is serious, the "g" end should be used and the "g" end should be connected to the shielding layer or shell. After the line is connected, the handle can be turned clockwise. The shaking speed should be slow and fast. When the speed reaches about 120 RPM (zc-25 type), keep rotating at a constant speed, and read after 1 minute, and read while shaking. Do not stop reading.

6. Put the megger at the horizontal position during the shaking measurement, and there is no short circuit between the end buttons when the handle is rotated. Shake the handle slowly and quickly. If the pointer points to zero, it means that the insulation under test may be short circuited. At this time, it is not allowed to continue shaking the handle to prevent the coil in the meter from heating and damaging.

7. After reading, discharge the measured equipment. The discharge method is to take down the ground wire used in the measurement from the megger and connect it with the equipment under test (not the discharge of the megger).

9、 Use and maintenance



Before measurement, the power supply of the tested equipment should be cut off, and the conductive part of the equipment should be connected with the earth for full discharge to ensure safety. The electrical equipment measured by digital megohmmeter should be grounded and discharged in time before re measurement.




Before measurement, check whether the digital megger is in good condition. That is, before the digital megger is connected to the measured object, turn on the power switch to detect the battery condition of the digital megger. If the battery of the digital megger is under voltage, the battery should be replaced in time, otherwise the measurement data is not acceptable. Insert the test line into the terminal "line (L) and ground (E)", select the test voltage, disconnect the test line, press the test button, and observe whether the number displayed is infinite. Short circuit the terminal "line (L) and ground (E)" and press the test button to observe whether "0" is displayed. If the LCD does not display "0", it indicates that the digital megohmmeter is faulty and should be reused after maintenance. The wiring must be correct. Generally, there are three terminals on the digital megger, which are marked with L (line), e (ground) and G (shield). Among them, l is connected to the insulated conductor part of the measured object and the earth, e is connected to the shell or ground of the measured object, and G is connected to the shielding of the measured object or the part that does not need to be measured. The terminal G is used to shield the surface current. For example, when measuring the insulation resistance of cables, due to the leakage current on the surface of insulating materials, the measurement results will be inaccurate, especially in the case of high humidity and the cable insulation surface is not clean, the measurement error will be very large. In order to avoid the influence of surface current, a metal shielding ring is added on the surface of the measured object and connected with the "shielding" terminal of the digital megohmmeter. In this way, the surface leakage current IB starts from the positive pole of the generator and flows back to the negative pole of the generator through the terminal g to form a circuit. IB no longer passes through the measuring mechanism of megohmmeter, so the influence of surface leakage current is eliminated fundamentally. The conductor between the terminal and the equipment under test shall not use double insulated wire or stranded wire, but shall be separately connected with single stranded wire to avoid error caused by poor insulation of stranded wire. In order to obtain the correct measurement results, the surface of the tested equipment should be wiped clean with clean cloth or cotton yarn. When measuring the insulation resistance of equipment with large capacitance, do not disconnect the megger immediately after reading, otherwise the charged capacitor will discharge the megger, which may burn the megger. After reading, the test line shall be disconnected first, and then the test shall be stopped. Before the megger and the tested object are fully discharged, the conductive part of the equipment under test shall not be touched by hand. When measuring the insulation resistance of the equipment, the temperature, humidity and relevant conditions of the tested object should also be recorded, so as to facilitate the analysis of the measurement results.

10、 Precautions



1. It is forbidden to measure the insulation resistance in the lightning or near the high-voltage equipment, only when the equipment is not charged and there is no induced current.

2. In the process of shake test, no one can work on the equipment under test.

3. The megohmmeter wires should not be twisted together, but separated.

4. Do not touch the megger by hand before it stops rotating or before the tested equipment is discharged. Do not touch the metal part of the lead wire when removing the wire.

5. At the end of the measurement, discharge the large capacitance equipment.

6. The insulation of measuring flexible wire from the terminal of megger shall be good, and proper distance shall be kept between two conductors and between conductor and ground, so as not to affect the measurement accuracy.

7. In order to prevent the surface leakage resistance of the tested equipment, when using the megger, the intermediate layer (such as the inner insulation between the cable shell and core) of the tested equipment should be connected to the protection ring.

8. Check its accuracy regularly.




（1） Calibration procedure



1. The range is 103 to 1012 with an impedance bridge with an accuracy of 1%. Relative humidity hygrometer high accuracy thermometer.

2. Open the meter cover and be careful not to damage the two wires connecting the power switch on the circuit board.

3. Locate the three calibration pots at the bottom right of the circuit board.

4. Make the meter in this environment for at least 1 / 2 hours, and then start the test after self balancing.

5. Connect one end of acl-800 meter with alligator clip and banana plug at the other end.

6. Insert a 3.5mm long plug into the socket of the meter.

7. Connect both ends of resistor with alligator clip.

8. Three calibration regulators, the top one is "humidity" measurement, the middle is "impedance", and the bottom is "temperature adjusted with a small screw driver". Clockwise direction is the increase value adjustment, the counter clockwise direction is the decrease value adjustment.

9. Press the power switch and compare the "temperature", "humidity" and "resistance" values at the same time.

10. Release the power switch and slowly adjust the corresponding correction regulator.

11. Press the power switch again and observe the LCD display.

12. If recalibration is needed, press the power switch again and adjust the corrector.

Tighten the four screws and cover the watch.

14. Press the power switch to make sure the meter is working properly.




（2） Resistance measurement



This measurement method is used to measure the surface resistance between a point on the surface of an object and another ground point on the surface. The measurement method conforms to the EOS / ESD s4.1 measurement standard.

A. Insert one end of the two wires into the two 3.5mm sockets of the meter, then connect one end to the alligator clip and the other to a 5-pound disc probe.

B. Connect the alligator clip to the known grounding point, and place the disc probe on the surface of the object to be measured according to the measurement requirements.

C. Press the measurement button until the resistance (in Ohm), relative humidity and temperature values are displayed on the display screen. The measurement results meet EIA, EOS / ESD, ANSI, iec-93, CECC and ASTM measurement standards. For the measurement of high impedance materials, in order to ensure high-precision measurement results, it is necessary to pay attention not to overlap the two leads, and do not touch the probe, lead and the measured object by hand.




Shandong Linyi Bosi conductive materials Co., Ltd. is a high-tech enterprise specializing in the production of MMO flexible anode, conductive polymer flexible anode and titanium coated anode, mainly providing corrosion protection, cathodic protection, engineering design, installation and technical services.