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Wire and Cable Quality Inspection

Date:Nov 27, 2019

1.Measurement of wire DC resistance:

The conductive core of the wire and cable mainly transmits 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 wire core resistance is larger due to the skin effect and the adjacent effect surface is stronger than the DC voltage. However, when the electric eye frequency is 50 Hz, the difference between the two is small. That can only require the DC resistance or resistivity of the test core to exceed the value specified in the standard. Through this inspection, some defects in the production process can be found, such as broken wires or partial single-wire breaks; Meet the standard; the length of the product is incorrect.

 

2.Insulation resistance test:

Insulation resistance reflects the important characteristics of the insulation properties of wire and cable products, and has a close relationship with the product's electrical strength, dielectric loss, and the gradual deterioration of the insulation under working conditions. For the communication cable, the insulation resistance between the lines is too low, which also increases the loop attenuation, the crosstalk between the circuits, and the long-distance power supply leakage on the conductive core. Therefore, the insulation resistance should be higher than the specified value.

 

3.Measurement of capacitance and loss factor:

When the cable is connected to the AC voltage, current flows. When the amplitude and frequency of the voltage are constant, the magnitude of the capacitor current is proportional to the capacitance of the cable (Cx). For ultra-high voltage cables, the current of such capacitors may reach a value comparable to the rated current, which is an important factor limiting 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, it can be found that various insulation degradation phenomena such as insulation moisture, insulation layer and shielding layer fall off, so capacitance and TAN δ measurement are performed in cable manufacturing or 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 electric field without breakdown damage. In order to check the quality of wire and cable products and ensure the safe operation of products, all insulation type wires and cables are generally tested for insulation strength. . The dielectric strength test can be divided into a withstand voltage test and a breakdown test. The voltage of time is generally higher than the rated working voltage of the sample, the specific voltage value and the withstand voltage time, which are specified in the product standard. Through the withstand voltage test, the reliability of the product operating under the working voltage can be tested and the seriousness of the insulation can be found. Defects, but also some shortcomings of the production process

 

 5.Aging and stability test:

The aging test is a stability test that maintains stable performance under the action of stress (mechanical, electrical, and thermal). Heat aging test: A simple heat aging test is a test of the aging characteristics of a test product under the action of heat. The test sample is placed in an environment above a rated temperature of the rated working temperature, so that at a higher temperature T, Shorter life.

 

6.Thermal stability test:

The thermal stability test is that the cable is heated by the current while still receiving a certain voltage. After a certain period of heating, some sensitive performance parameters are measured to evaluate the stability of the insulation. The insulation stability test is divided into two types: long-term stability test or short-term accelerated aging test.

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