NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
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NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
Author: Noyafa–Cable Locator Suppliers
What are the factors affecting insulation resistance? 1. Ambient temperature and humidity The insulation resistance value of general materials decreases with the increase of ambient temperature and humidity. Relatively speaking, the surface resistance (rate) is more sensitive to ambient humidity, while the bulk resistance (rate) is more sensitive to temperature. As humidity increases, surface leakage increases, and conductor conductance current increases.
As the temperature rises, the movement rate of carriers increases, and the absorption current and conduction current of the dielectric material will increase accordingly. According to relevant data reports, the resistance value of the general dielectric at 70°C is only 10% of that at 20°C. Therefore, when measuring insulation resistance, it is necessary to specify the temperature and humidity at which the sample and the environment reach equilibrium. 2. When a certain DC voltage is used to pressurize the material under test during the test time, the current on the material under test does not reach a stable value instantaneously, but has a decay process.
At the same time of pressurization, a large charging current flows, followed by a slowly decreasing absorption current for a long time, and finally a relatively stable conductance current is achieved. The higher the resistance value being measured, the longer it takes to reach equilibrium. Therefore, in order to correctly read the measured resistance value during measurement, the value should be read after stabilization.
It is stipulated in the test method of insulation resistance of communication cables that the reading after charging for 1 minute is the measured value of the insulation of the cable. However, in practice, this method is somewhat inappropriate, because when the DC voltage pressurizes the material to be tested, the current on the material to be tested is a capacitive current. Since it is a capacitive current, it is related to the capacitance of the cable, and the large capacitance needs to be charged. The longer it takes, especially the ointment-filled cable, which takes longer. Therefore, for the same type of cable, due to different lengths and different capacitances, the reading when the charging time is one minute is obviously unscientific, and further research and discussion are needed.
3. Factors of the cable itself When the cable is heated and damp, the insulating material will age. Its insulation resistance is reduced. 4. Accurate use of test instruments Many manufacturers of test instruments generally use high-resistance meters and megohmmeters. When working, the instrument itself generates high voltage, and the measurement object is electrical equipment, so it must be used correctly, otherwise it will cause personal injury or damage. Equipment accident.
Before use, first make the following preparations: (1) Before measurement, the power supply of the device under test must be cut off and short-circuit discharge to the ground. Never allow the device to be measured with power on to ensure the safety of people and equipment. (2) For equipment that may induce high-voltage electricity, this possibility must be eliminated before measurement can be performed. (3) The surface of the measured object should be clean to reduce the contact resistance and ensure the correctness of the measurement results.
(4) Before measuring, check whether the instrument is in normal working condition, mainly check its“0”and“∞”two o'clock. The megohmmeter is to shake the handle to make the motor reach the rated speed. The megohmmeter should refer to the“0”position, open circuit should refer to“∞”Location. (5) The instrument should be placed in a stable and firm place, away from large external current conductors and external magnetic fields.
After the above preparations are done, the measurement can be carried out. When measuring, pay attention to the correct wiring, otherwise it will cause unnecessary errors or even mistakes. What are the factors affecting insulation resistance? Shenzhen Noyafa Electronic Technology Co., Ltd.
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