Three important indicators on wire and cable quality testing
The selection of qualified wire and cable products relates to the safety of people's production and life. For the average consumer, besides mastering how to choose qualified wire and cable products, it is also necessary to understand the general monitoring knowledge of wire and cable. In the detection of wire and cable quality, there are mainly the following important indicators.
Insulation resistance test:
The insulation resistance type reflects the important index of insulation properties of wire and cable products. It is closely related to the strength of the product, dielectric loss, and the gradual deterioration of the insulation material under working conditions. For communication cables, too low insulation resistance between lines will also increase loop attenuation, crosstalk between loops, and long-distance power supply leaks on conductive cores, etc. Therefore, the insulation resistance should be higher than the specified value.
At present, the measurement of the insulation resistance of wire and cable, in addition to the use of ohmmeter (rocking table), commonly used galvanometer comparison method high resistance meter method (voltage - current method).
Capacitance and loss factor Test:
When the AC voltage is applied to the cable, current flows. When the voltage amplitude and frequency are constant, the capacitor current is proportional to the cable capacitance (Cx). For ultra high voltage cables, the current of this capacitor may reach a value comparable to the rated current, which becomes an important factor limiting the capacity of the cable and the transmission distance. Therefore, the capacitance of the cable is also one of the main electrical performance parameters of the cable.
Partial discharge Test:
There is basically no local power generation for oil-filled cables; oil-paper cables are usually very weak, such as several PCs, even if there is partial discharge, so these cables may not measure partial discharge in the factory test. For the extruded cable, not only is the possibility of partial discharge generated, but also the damage of the partial discharge to the plastic and rubber is severe. With the increase of the voltage level and the improvement of the work field, this problem becomes even more serious. Extruded cables are subject to partial discharge measurements in the factory test.
Partial discharge measurement methods are many, according to the instantaneous charge exchange generated by the discharge, measuring the discharge pulse (electrical measurement); can also be measured according to the ultrasonic wave generated during discharge (sound measurement method); also based on the discharge of light , measure the intensity of light (photometric method). Basically, electrical measurements are used for cables.