The selection of qualified wire and cable products is related to the safety of people's production and life. For ordinary consumers, in addition to mastering how to select qualified wire and cable products, it is also necessary to understand the routine monitoring knowledge of wire and cable. In terms of wire and cable quality inspection, there are mainly the following important indicators.

　　Insulation resistance test:

　　Insulation resistance is an important index to reflect the insulation characteristics of wire and cable products. It is closely related to the electrical strength, dielectric loss and gradual deterioration of insulation materials under working conditions. For communication cables, too low insulation resistance between lines will also increase loop attenuation, crosstalk between loops and leakage of long-distance power supply on conductive cores. Therefore, it is required that the insulation resistance should be higher than the specified value.

　　The defects in the process can be found by measuring the insulation resistance, such as the insulation is not dry or the sheath is damaged and damp; Insulation is polluted and conductive impurities are mixed; Insulation layer cracking caused by various reasons. During the operation of wires and cables, the insulation resistance and leakage current shall be frequently detected as the main basis for whether the safe operation can be continued.

　　Measurement of capacitance and loss factor:

　　When AC voltage is applied to the cable, current flows. When the voltage amplitude and frequency are constant, the capacitance current is proportional to the capacitance (Cx) of the cable. 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 cable capacity and transmission distance. Therefore, the capacitance of the cable is also one of the main electrical performance parameters of the cable.

　　Through the measurement of capacitance and loss factor, various insulation deterioration phenomena such as insulation moisture, insulation layer and shielding layer falling off can be found. Therefore, the capacitance and Tan are measured in the cable manufacturing or cable operation. For high-voltage cables, CX and Tan are measured under their working conditions, i.e. power frequency high voltage. Usually, high-voltage Xilin bridge is used. This year, transformer bridge with current ratio has also been used.

　　Partial discharge measurement:

　　There is basically no local power generation for oil filled cables; Even if the oil paper cable has partial discharge, it is usually very weak, such as several PCs. therefore, the partial discharge of these cables can not be measured in the factory test. For extruded cables, not only the possibility of partial discharge is high, but also the damage of partial discharge to plastics and rubber is serious. With the improvement of voltage level and working field strength, this problem becomes more serious. Therefore, partial discharge measurement shall be carried out for high-voltage extruded cables in factory test.