The principle of measuring insulation with a megger is that the insulation resistance to be measured is connected between terminals "L" and "E". However, when the leak on the surface of the insulation to be measured is detected. serious, the shielding ring of the tested object must be removed or not. The measured part is connected to terminal “G”. In this way, the leakage current returns directly to the negative terminal of the generator through the shield terminal “G” to form a loop, and the insulation is measured.
Three binding posts (i.e. L: line end, E: ground end, G: shield end)
When using When using a megger to measure the insulation resistance of electrical equipment, there must be It should be noted that the “L” and “E” terminals cannot be connected backwards. The correct connection method is: the "L" wire terminal is connected to the conductor of the equipment under test, the terminalearth “E” is connected. connected to the shell of the grounded equipment, and the shield terminal “G” is connected to the conductor of the device under test.
If "L" and "E" are connected in reverse, the leakage current flowing through the interior and surface of the insulator will be collected to ground through the shell and s The loss of the shielding effect will cause large errors in the measurement.
In addition, since the degree of insulation between the internal wire of the "E" end and the case is less than that between the "L" end and the case, when the megger is placed to the ground and used in the correct wiring method, the insulation resistance of the "E" end to the instrument shell and the shell to the ground is equivalent to a short circuit and will not cause errors when “L” and “E” are connected backwards. the insulation resistance of “E” to the terre is the same as the measured insulation resistance. Parallel connection will reduce measurement results and cause larger measurement errors.
It can be seen that to accurately measure the insulation resistance of electrical equipment, etc., the megger must be used correctly, otherwise the measurement accuracy and reliability will be lost.
Detailed information
Notes on use:
1. It is prohibited to measure insulation resistance during lightning or near high voltage. Measure when the device is not powered and no electricity is induced.
2. During the shake test, no one may work on the equipment under test.
3. When measuring the insulation resistance of the equipment, the power supply to the equipment should first be turned off. Equipment containing inductors and capacitors (such as capacitors, tr(formers, motors and cable lines) must be unloaded first. Off-duty personnel must request corresponding work tickets before they can work.
4. The oscillator must be placed horizontally. Before wiring, you need to shake the oscillator and observe whether the pointer is at "∞". Then short-circuit terminals L and E and slowly shake the watch. The needle should be at zero. After open circuit and short circuit tests, the megger is confirmed to be intact before measurement can be made.
5. The megger wire should be a multi-strand soft wire, and the two wires should not be twisted together to avoid inaccurate measurement data.
6. After the megger measurement is completed, the measured object should be unloaded immediately. Before the megger stops rotating and the measured object is discharged, do not touch the measuring part of the measured objectOr. disassemble it with your hands to avoid electric shock.
7. The surface of the object to be measured should be wiped clean and there should be no dirt (such as paint, etc.) to avoid inaccurate measurement data.
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How to stabilize the voltage of a hand-cranked generator
The working principle of a generator manually operated: There are two coils connected to the needles of the manual generator, one with the same additional resistance R in the meter is connected in series, the other is connected in series with the measured resistance R, and then connected together to the manual generator. When the generator is started by hand, current flows through both coils at the same time and torques in opposite directions are generated on the two coils. The watch hands flex at a certain angle depending on the combined torque of the two couples. This deviation The angle est determined by the ratio of the two currents. The additional resistance is constant, so the current value only depends on the size of the resistance to be measured. Instructions for use: Before measurement, the megger should be held in a horizontal position, hold the meter body with your left hand, and shake the rocker handle with your right hand at about 120 rpm. The pointer should point to infinity (∞). , otherwise the megger is defective. Before measurement, the power supply to the electrical apparatus and circuit under test should be cut off, and the relevant components should be temporarily grounded and discharged to ensure the safety of people and the megger and the accuracy of the results. measurement. Correct wiring must be used when measuring. The megger has 3 terminals (L, E, G). When measuring loop resistance to ground, the L end is connected to the exposed loop conductor and the L endemitted E is connected to the ground wire or metal shell when measuring the insulation resistance of the loop, the first and; the last ends of the loop are connected to L and E respectively; cable insulation is measured when measuring resistance, in order to prevent leakage current on the cable surface from affecting the measurement accuracy, the cable shielding layer should be connected to the terminal G. The flexible measuring wire coming from the megger terminal should be well insulated and a proper distance should be maintained between the two wires and between the wire and the ground to avoid affecting the measurement accuracy. When shaking the oscillator, do not touch the terminals of the oscillator and the circuit under test with your hands to avoid electric shock. After shaking the watch, do not short the terminals to avoid damage. Do not shake the watch for too long.
Why the megger generatesIs there DC voltage?
This is a process and review for making a crank feeder. If there is an error, please report:
If it is a direct low voltage hand crank charger. generator (the default output settings level is 50V/20Hz low voltage and low frequency), you can add a bridge rectifier to transform alternating current into direct current output, and then connect a light-emitting diode corresponding to the voltage in parallel (you can connect a resistor) to limit its voltage, so that the output voltage is limited to the parallel connection. The voltage at both ends of the light-emitting diode is considered the limit and stability of the voltage, so you can connect it; a DC0.5~5V to DC5V power module sold in an online store (if the module can withstand the unstable or high voltage of the generator, you can omit the conparallel connection of the light-emitting diodes on the front if you are charging). the phone directly, it is very likely that the crank will be unstable and cause a power outage. The phone will still answer, which will consume more power. It is recommended to purchase a simple set of power bank connection modules (preferably without). buttons, with a charging indicator light or digital voltage display) to the cylindrical lithium battery of the power bank to make it a simple power bank. In this way, the cell phone can be charged indirectly via the power bank without interruption. disappeared.
Because the megger uses a high voltage DC generator to generate a high DC voltage.
There are three binding terminals of the megger: one is "L" which is the line terminal, one "E" is the ground terminal and the other "G" is the shield terminal (also called protection terminal). annprotective water). Generally, the insulation resistance to be measured is connected between terminals "L" and "E". However, when the surface leakage of the insulation to be measured is serious, the shielding ring of the tested object or the. the part that does not need to be measured should be connected to the "G" terminal.
In this way, the leakage current returns directly to the negative terminal of the generator through the shielded terminal "G" to form a loop, instead of flowing through the measuring mechanism (moving coil) of the megger. .
This basically eliminates the influence of surface leakage current. In particular, it should be noted that when measuring the insulation resistance between the cable core and the surface, the shield terminal "G" should be connected, since when the air humidity is high or the cable insulation surface is not clean, the leakage current on its surface will be very large. In order to prevent the measured object from affectingMeasuring internal insulation due to leakage, a metal shield ring is usually added. the outside of the cable. Connect to the “G” terminal of the megger.
Detailed information
Notes:
1. It is prohibited to measure insulation resistance during lightning or near high voltage equipment. The measurement is performed when the equipment is not powered and there is no induced electricity.
2. During the shake test, no one may work on the equipment under test.
3. When measuring the insulation resistance of the equipment, the power supply to the equipment should first be turned off. Equipment containing inductors and capacitors (such as capacitors, transformers, motors and cable lines) should be discharged first. Off-duty personnel must request corresponding work tickets before they can work.iller.
4. The oscillator must be placed horizontally. Before wiring, you need to shake the oscillator and observe whether the pointer is at "∞". Then short-circuit terminals L and E and slowly shake the watch. The needle should be at zero. After open circuit and short circuit tests, the megger is confirmed to be intact before measurement can be made.
5. The megger wire should be a multi-strand soft wire, and the two wires should not be twisted together to avoid inaccurate measurement data.
6. After the megger measurement is completed, the measured object should be unloaded immediately. Before the megger stops rotating and the measured object is discharged, do not touch the measuring part of the measured object or. disassemble it with your hands to avoid electric shock.
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