To measure the insulation resistance, generally use an insulation resistance tester to test. Insulation resistance tester is also called digital megohmmeter, pointer megohmmeter, insulation meter, insulation resistance tester, high-voltage insulation resistance tester, insulation resistance measuring instrument, insulation characteristic tester, high-voltage megohmmeter, with absorption ratio function Megger, megohmmeter with polarization index function, electric shaker, electronic insulation resistance tester, high-power and high-voltage megohmmeter, etc.

(1) Principle of insulation resistance tester:

The insulation resistance tester mainly uses a voltage to excite the device or network under test, and then measures the current generated by the excitation, and uses Ohm's law to measure the resistance. For example, compared with the ohmmeter function equipped on a digital multimeter (DMM), these electrical testers apply a much higher voltage when making resistance measurements. The voltage range used by the megohmmeter is usually from 50V to as high as 5 kV; and the voltage of a typical digital multimeter is generally less than 10 V. For insulation testing, the resistance value range that needs to be measured is very large, the upper limit can reach 10TΩ, and the required voltage is higher.

(2) Performance of insulation resistance tester:

Insulation resistance testers, usually called megohmmeters or high resistance meters, are widely used to measure generators, motors, power transformers, wiring, electrical appliances and other electrical devices (such as control, signal, communication and power cables) Insulation resistance. They are often used in routine maintenance procedures to indicate changes in the insulation resistance of motors over months or years. A large change in insulation resistance may indicate a potential failure. Therefore, the megohmmeter needs to be calibrated regularly to ensure that the meter itself does not change over time.

(3) How to use the insulation resistance tester:

When the insulation tester is working, it generates high voltage by itself, and the measurement object is electrical equipment, so it must be used correctly, otherwise it will cause personal or equipment accidents. Before using the megohmmeter, you must first make the following preparations:

(1) Before measurement, the power supply of the equipment under test must be cut off and short-circuited to the ground. Never allow the equipment to be charged for measurement to ensure the safety of persons and equipment

(2) For equipment that may induce high voltage, the measurement must be eliminated after this possibility.

(3) The surface of the measured object should be clean to reduce the contact resistance to ensure the accuracy of the measurement result.

(4) Before measurement, check whether the megohmmeter is in normal working condition, mainly check its "0" and "∞" two points. That is, shake the handle of the hand-cranked generator to make the motor reach the rated speed. When the megger is short-circuited, the pointer should point to the "0" position; when it is open, the pointer should point to the "∞" position.

(5) When using the insulation tester, it should be placed in a stable and firm place, and far away from large external current conductors and external magnetic fields.

(6) The wiring must be correct. There are generally three terminals on the megohmmeter, of which L is connected to the conductor part insulated from the ground, and E is connected to the outer 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. When measuring the insulation resistance, generally only the "L" and "E" terminals are used. But when measuring the insulation resistance of the cable to the ground or the leakage current of the device under test is serious, it is necessary to use the "G" terminal and connect the "G" terminal to the shielding layer or the shell. After the line is connected, you can turn the crank in a clockwise direction. The shaking speed should be slow and fast. When the speed reaches about 120 revolutions per minute (ZC-25 type), keep rotating at a constant speed, and read after 1 minute. And read while shaking. Can't stop to read.

(7) Place the megger in a horizontal position during panning, and no short circuit between the end buttons is allowed when the handle is turned. Shaking the handle should be slower and faster. If you find that the pointer is pointing to zero, it means that the insulation under test may have a short circuit. At this time, you cannot continue to shake the handle. To prevent heating and damage of the coil in the watch.

The reading is complete. Discharge the device under test. The discharge method is to remove the ground wire used in the measurement from the megohmmeter and short-circuit the device under test (not the insulation tester discharge).

(4) Precautions for insulation resistance tester:

(1) It is forbidden to measure the insulation resistance during lightning or near high-voltage equipment, only when the equipment is not live. It is also measured without induced electricity.

(2) During the telemetry process. No one can work on the device under test.

(3) The insulation tester wires cannot be twisted together. To be separated.

(4) Before the megger stops rotating or before the device under test is discharged. Do not touch with your hands. When removing the wire, do not touch the metal part of the lead.

(5) At the end of the measurement. For large-capacitance equipment, discharge.

(6) The measurement cord from the megohmmeter terminal should be well insulated, and a proper distance should be kept between the two wires and between the wire and the ground, so as not to affect the measurement accuracy.

(7) In order to prevent the surface leakage resistance of the equipment under test, when using a megohmmeter. The intermediate layer of the device under test (such as the inner insulation between the cable shell cores) should be connected to the protective ring.

(8) Check its accuracy regularly.