Using a megger can only detect a short in the wire, but not the specific location of the short.
To detect a short circuit in a wire using a megger, the two measuring leads are in contact with three conductor wires respectively, and the other end of the cable is open circuited if the cable resistance is reached. two phases tested is zero, this means that the phase is short-circuited.
Megger, also called megger, is mainly used to measure the insulation resistance of electrical equipment. The rated voltage of megger is 500, 1000, 2500V, 5000V, 10000V, etc., and there are manual and electronic types.
Detailed information:
Preparation
When the megger works, it generates high voltage and the measuring object is an equielectrical equipment, it must therefore be used correctly. Otherwise, personal or material accidents could occur. Before use, you should first make the following preparations
(1) Before measurement, the power supply of the equipment under test should be cut off and short-circuited to ground.
(2) For equipment capable of inducing high voltage electricity, this possibility must be eliminated before the measurement can be made.
(3) The surface of the object to be measured should be clean to reduce contact resistance and ensure the accuracy of the measurement results.
(4) Before measurement, check whether the megger is in normal working condition, mainly check its "0" and "∞" points. In other words, shake the handle so that the motor reaches rated speed. The megger should point to the “0” position when shorted, and it should point to the “∞” position when shorted.in open circuit.
(5) When using the megger, it should be placed in a stable and solid place away from large external current conductors and external magnetic fields.
References:
Use of Megometer
Purpose: In order to avoid accidents, it is used to measure the insulation resistance of various electrical equipment Megohm class resistance meter, megohmmeter is convenient and reliable for measuring insulation resistance.
Instructions for use:
1. 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. ensure the safety of people and the megger and the measurement results are accurate.
2. The wiring must be correct whenmeasure. The megger has three terminals (L, E, G). When measuring the resistance of the loop to ground, the L end is connected to the exposed conductor of the loop and the E end is connected to the ground wire or metal shell when measuring the resistance d 'loop isolation, the first and; the last ends of the loop are connected to L and E respectively; the resistance of the cable insulation is measured, to prevent the leakage current on the cable surface from affecting the measurement accuracy.Connect the cable shield to the G terminal.
3. 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.
4. When shaking the megger, do not touch the megger terminals and the circuit under test with your hands to avoid electric shock.
5. After shaking the megger, do not short circuit the terminals to avoid damage.
6. Don't shake the megger for too long.
Detailed information:
1. It is prohibited to measure insulation resistance during lightning or near high voltage equipment. It can only be measured when the equipment is not charged 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 ticketsbefore being able to 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 leads of the megger should be multi-stranded flexible wires, and the two wires should not be twisted together to avoid inaccurate measurement data.
Reference documents:
Meter, also known as megger, is an instrument used to measure insulation resistance and large value resistance of l equipment tested. a hand crank generator, it consists of a meter collectorand three connection terminals (i.e. L: line terminal, E: earth terminal, G: shield terminal).
1. Principles of selection of megohmmeters
(1) Selection of the rated voltage level. Generally speaking, for equipment with a voltage rating below 500 V, a 500 V or 1000 V megger should be used; For equipment with a rated voltage above 500V, a 1000V~2500V megometer should be used.
(2) Resistance range selection. There are two small black dots on the scale of the megger dial, and the area between the small black dots is the precise measurement area. Therefore, when selecting a table, the insulation resistance value of the equipment under test should be within the precise measurement area.
2． Use of oscillator
(1) Calibration of the counter. Before measurement, the megometer must be subjected to an open circuit and short circuit test to verifyCheck if the megometer is in good condition. Open the two connecting wires, shake the handle, the pointer should point to "∞", then connect the two connecting wires. Short circuit the wires and the pointer should point to "0". Those that meet the above conditions are good, otherwise they cannot be used.
(2) The equipment under test is disconnected from the line and the large capacity equipment must be unloaded.
(3) Select a megger with a constant voltage level.
(4) When measuring insulation resistance, only the "L" and "E" terminals are generally used, but when measuring the insulation resistance of the cable at the earth or leakage current of the equipment under test is serious, it is necessary to use terminal "G", and connect terminal "G" to the shield or to the case. After the circuit is connected, you can turn the shake handle clockwise. Shaking speed should be slowto fast. When the rotating speed reaches about 120 revolutions per minute (ZC-25 type), continue rotating at a constant speed and take. reading after 1 minute. Take the measurements by shaking and don't stop to read.
(5) Remove the stitches and unload them. When the reading is complete, shake slowly while removing the wires, then discharge the device under test. The discharge method involves removing the ground wire used during measurement from the megometer and short-circuiting it with the device under test (without discharging the megometer).
4． Notes
(1) It is prohibited to measure insulation resistance during lightning or near high voltage equipment. It can only be measured when the equipment is not charged and there is no induced electricity.
(2) During the shake test process, no one can work on the equipment under test.
(3) The meter wires cannot be twisteded together, but must be separated.
(4) It is strictly forbidden to touch the megger with bare hands before it stops rotating or before the device under test is discharged. When removing the wires, do not touch the metal parts of the cables.
(5) At the end of the measurement, large capacity equipment must be unloaded.
(6) Check its accuracy regularly.