Several important indicators of cable quality inspection

For the quality inspection department, testing the quality of wires and cables may require testing more than two dozen projects. For a cable, the following six important measurement items play a key role in determining its quality. effect.

1, the direct current resistance measurement of the wire:

For wire and cable, the conductor part is its most important part. Wire and cable conductive cores mainly transmit electrical energy or electrical signals.

The resistance of the wire is the main indicator of its electrical performance. Now the standard stipulates: whether the DC resistance or resistivity of the test core exceeds the value specified in the standard.

The main purpose of this test is to find out certain defects in the production process: if the wire breaks or some of its single wire breaks; the cross section of the wire does not conform to the standard; the length of the product is not correct.

In addition, for the power cable, this test can not only detect the condition of the conductor, but also detect whether the conductor has influence on the allowable ampacity in the operation of the wire and cable product.

2, 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.

The determination of insulation resistance can be found in the process of defects: If the insulation is dry or jacket moisture damage; insulation is contaminated and mixed with conductive impurities; various causes of insulation cracking.

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. Therefore, the insulation resistance should be higher than the specified value. In the operation of wires and cables, insulation resistance and leakage current are often tested as the main basis for whether or not safe operation can continue.

3, the measurement of capacitance and loss factor:

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

In an AC electric field, insulators in the cable, due to leakage currents and various polarizations, generate dielectric losses, represented by the dielectric loss factor or loss tangent (TAN δ), which not only wastes power, but also makes the dielectric (insulator) ) Heating, accelerated insulation aging, so TANδ is also one of the main parameters of the cable.

The measurement of capacitance and loss factor can reveal that the insulation is damp, the insulation layer and the shielding layer fall off, and other insulation degradation phenomena. Therefore, both capacitance and loss tangent values ​​are measured during cable manufacturing or cable operation. For high-voltage cables, the measurement of capacitance and loss factor is carried out under its operating conditions, ie at high power frequency.