1. Inspection method
Routine test: It is an experiment conducted by the manufacturer on all finished cables. Its purpose is to check whether the quality of the product meets the requirements of the technical conditions in order to find accidental defects in the manufacturing process. It is a non-destructive experiment, such as the DC resistance of the wire and the insulation resistance time. And withstand voltage test, partial discharge detection, etc.
Type test: It is the manufacturer who regularly conducts comprehensive performance inspection of the product, especially for a new product before it is finalized for mass production, or the structure, material and main process of a product have changed, which may affect the performance of the cable Time. Pass type test: It can be tested whether the product can meet the requirements of operation, and can be compared with the old product. Such as thermal aging performance of insulation and sheath, long-term stability test of power cable, etc.
Acceptance test: It is an acceptance test performed on the cable after the cable is installed and laid in order to check the installation quality and find possible damage during the construction. Such as withstand voltage test after installation.
2. Test items
2.1 Measurement of DC resistance of wires
The conductive core of the wire and cable mainly transmits electric energy or electric signal. The resistance of the wire is the main indicator of its electrical performance. When the AC voltage is applied, the core resistance is larger due to the skin effect and the adjacent effect surface than when the DC voltage is applied, but the difference between the two is very small when the electric eye frequency is 50Hz. The current standard stipulates That can only require the detection of whether the DC resistance or resistivity of the 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 partial single wire breakage; Meet the standard; the length of the product is incorrect, etc. For aerial bundled cables 1418 standard, you can also check whether it will affect the allowable current carrying capacity of wire and cable products during operation.
There are single-arm DC resistance method and double-arm DC bridge method to measure the DC resistance of conductors. The accuracy of the latter is higher than that of the former. The test procedure is also more complicated than the former.
2.2 Test of insulation resistance
Insulation resistance is an important indicator reflecting the insulation characteristics of wire and cable products. It is closely related to the product’s electrical strength, dielectric loss, and the gradual deterioration of insulating materials under working conditions. For communication cables, low insulation resistance between wires will also increase loop attenuation, crosstalk between loops, and long-distance power supply leakage on conductive cores. Therefore, insulation resistance should be higher than the specified value.
Defects in the process can be found by measuring the insulation resistance, such as the insulation is dry and impermeable or the sheath is damaged and damp; the insulation is contaminated and conductive impurities are mixed in; the insulation layer is cracked due to various reasons. In the operation of aerial bundled cables(abc) sans1418, the insulation resistance and leakage current are often tested as the main basis for continued safe operation.
At present, in addition to the ohmmeter (shaking meter), the current measurement of the insulation resistance of wires and cables is the galvanometer comparison method and the high resistance meter method (voltage-current method).