1. Measurement of DC resistance
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. When the AC voltage is applied, the core resistance is larger than the DC voltage due to the skin effect, but when the frequency of the eye is 50Hz, the difference between the two is very small. Now the standard stipulates that all can only be required to check whether the DC resistance or resistivity of the wire core exceeds the value specified in the standard. Through this inspection, certain defects in the production process can be found, such as wire breakage or part of the single wire breakage; the wire cross-section doesn’t meet the standard; the length of the product is not correct, etc.
2. Insulation resistance test:
The insulation resistance type reflects the important index of insulation properties of wire and cable products and 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, if insulation resistance between wires is too low 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.
3. The measurement of capacitance and loss factor:
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. 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, capacitance and TANδ are measured both in cable manufacturing and cable operation.
4. Insulation strength test:
The insulation strength of wire and cable refers to the ability of insulation structure and insulation material to withstand the effect of the electric field without breakdown. In order to check the quality of wire and cable products and ensure the safe operation of products, all insulation types of wire and cable are generally tested for insulation strength. Dielectric strength test can be divided into pressure test and breakdown test. The timing voltage is generally higher than the rated working voltage of the test product. The specific voltage value and withstand voltage time are stipulated in the product standards. The withstand voltage test can test the reliability of the product under the working voltage and find the seriousness of the insulation. Defects, but also can find some shortcomings of the production process.
5. Aging and stability test:
Aging test is the stability test that can maintain stable performance under stress (mechanical, electrical, and thermal). Heat Aging Test: A simple heat aging test is a test of the aging property of the test sample under the influence of heat. The test product is placed in an environment with a certain value higher than the rated operating temperature, so that at a higher temperature T, then the Shorter life is.
6. thermal stability test:
The thermal stability test is that the cable is heated by the current while it is also subjected to a certain voltage. After a certain period of heating, certain sensitive performance parameters are measured to evaluate the stability of the insulation. Insulation stability test is divided into long-term stability test or short-term accelerated aging test.