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Testing items and methods of wire and cable
Jan 26, 2018

The rapid development of power industry is an important guarantee for the economic development of a country, and wire and cable is an essential product in the process of power construction. At present, China's wire and cable industry has jumped into the first manufacturing country. However, the current domestic quality of wire and cable is also more prominent, the resulting fire or other safety accidents are common, worrying, needs in the production process in accordance with national standards, according to scientific methods, do a good job of each project detection, to strengthen supervision to provide scientific and accurate basis.

At present, the domestic production of wire and cable manufacturers and messy, uneven production technology, the industry's quality assurance system is not perfect, leading to the production of China's wire and cable product quality and other developed countries have a large gap. In addition, some manufacturers for the pursuit of high profits, the use of substandard raw materials and production technology, further leading to fake and shoddy wire and cable products flooded the domestic market. In recent years, the State has gradually attached importance to the detection of wire and cable, and has formulated some strict production and quality regulations, to a certain extent, to promote the quality of our wire and cable products improve.

Performance issues

Some of the domestic quality inspection agencies have a number of electrical wire and cable investigation, the results show that, in the production enterprises through the ISO9000 certification, its wire and cable can reach the passing rate is also under 90%, and those who did not pass the certification of small-scale wire and cable production enterprises, the product pass rate of not even up to 30%. According to the survey report issued by the quality inspection agencies, the market of various franchised stores sold wire and cable, the overall pass rate of roughly 70%, those smaller hardware stores, the distribution of the passing rate of the wire and cable is not even up to 10%. Domestic wire and cable quality is worrying.

Detection method

According to the relevant provisions of national standards, wire and cable testing items mainly include electrical properties and mechanical properties of two aspects of detection, including electrical performance testing mainly DC resistance detection, insulation resistance detection and power-frequency pressure detection and other aspects of the content.

(i) DC resistance detection.

Relevant national standards have a clear stipulation: the DC resistance of wire and cable should be compared with the conductor resistance per kilometer as the benchmark, the measured wire and cable DC resistance data must first be converted into 20 ℃ temperature per kilometer of DC resistance value. If the measured DC resistance is converted to the DC resistance value under the 20 ℃ condition, its value is less than the standard value, then the wire and cable sample is a qualified product, and the other is an unqualified product.

At present, the domestic relevant departments usually use the bridge method and the current method two methods to determine the DC resistance of wire and cable. The measuring range of the bridge method is narrow, which can be divided into single arm bridge method and double arm bridge method, when the electric wire and cable's resistance value is about 1 or more, the single arms bridge method is used; when the wire and cable resistance value is less than 1, the double Arms bridge method is used. The current method is also known as the micro-Euclidean method, the principle of which is based on the size of wire and cable resistance, the use of constant current source output different constant currents, and then accurately measure the voltage at both ends of the measured wire and cable, the measured data in accordance with the Ohm's law can be measured by the The current method can output different current, so its measurement range is relatively wide.

(b) Insulation resistance detection.

The insulation resistance measured value of wire and cable must be converted to the insulation resistance value of each kilometer, unlike the DC resistor, the insulation resistance value is inversely proportional to the length of the wire and cable; the measuring voltage of the insulation resistance of low-voltage wire and cable is 100V, 250V, 500V and 1000V four kinds, Among them, the testing voltage of 100V and 500V is widely used in the inspection department, and the length of the wire and cable is not specified, but for the convenience of measurement and calculation, it is generally taken 10m for measurement. The charge time before measurement is generally 1 minutes.

The insulation resistance of wire and cable is usually measured by voltage and current method, also known as high impedance meter method. Some wire and cable with metal protective sleeve, has a certain shielding function, for the insulation resistance measurement of the wire and cable, most of the insulation resistance between the conductor and the metal sleeve or shielding layer or armored layer is measured, while for the wire and cable without metal sheath, the measured wire and cable must be immersed in the water before measuring its insulation resistance value. Then the insulation resistance between the conductor and the water is measured, and the test sample must be maintained with the temperature.

At present, a DC resistance insulation resistance tester has been developed in China, which is simple to operate, the whole process of measurement can be controlled by computer, and the accuracy and stability are much higher than the traditional testing equipment zzj3d.

(iii) Power frequency withstand pressure detection.

Power frequency withstand voltage is generally used to detect. National standards: The AC voltage is used because the frequency of the approximate sine wave between 49hz~61hz; for the wire and cable rated voltage of voltages products, When the insulation thickness ≦0.6mm 1500V high-pressure, when the insulation thickness ≧0.6mm using 2000V high-pressure, pressure 5 minutes, if the test wire and cable samples do not occur breakdown or flashover is qualified products, the contrary is not qualified. For example, there is a specification for 60227IEC53 (RVV) 300/ 500v32.5 samples need to be pressed, then we have to put the 1th core of high pressure on the water, and then the 2nd core to high pressure on the water, and then the 3rd core-high pressure on the water, the final need all 3 cores to the water each dozen 1 times withstand pressure, a total need to play 4 times withstand pressure.

(iv) Mechanical performance testing.

The mechanical properties mainly refer to the tensile strength before and after the aging of wire and cable. Relevant national standards stipulate: the use of forced ventilation aging box to make the aging wire and cable samples, testing should be as close as possible to the aging part. The mechanical properties of the test are generally directly measured by electronic tensile instruments. The width and thickness of the middle part of the measured wire and cable are measured by the thickness gauge first, then the specimen is artificially aged in the blast dryer, then the electronic tensile machine is used to measure the elongation distance and the maximum tensile stress of the wire and cable during tensile fracture. The obtained data can be used to calculate the tensile strength and elongation at break before and after the aging of the wire and cable, and to judge whether the product is qualified by comparison with the product standard.

(v) Other testing items and testing methods.

In addition to the above major testing items, there are insulation thickness detection, size and mark detection, as well as the thickness of the sheath test items, these generally can be used some relatively simple measuring instruments or manual inspection can be. Insulation thickness refers to the thickness of all the protective layers on the insulating layer, measured by the projector and reading microscope, and compares the measured data with the standard of the product, the average value must be greater than the specified values for the qualified products. The external dimension can be measured with a projector or a wrapping belt, and the method of ellipse measurement is to measure the outer diameter of any two points on the same cross section of the circular sheath cable, take the difference, and then use the difference and the cable standard to stipulate that the mean OD ratio cannot exceed 15%. China's wire and cable signs of the failure rate is very high, the national Standard stipulates: The logo of wire and cable must have continuity and resistance to rub, and has a high definition, in which the rub needs to use the medical absorbent cotton alcohol gently rub 10 times, the printing is clear that is qualified.

Some countermeasures

(a) Increase publicity efforts to strengthen quality awareness. To put the propaganda and education work on the priority of special governance, to organize enterprises to learn the relevant laws and regulations, to openly deal with high-profile, to form a massive publicity and social supervision atmosphere.

(b) To combat counterfeit goods and standardize production and operation. Combating counterfeit and inferior products is an effective way to improve the quality of wire and cable at present to fight against counterfeiting from three aspects, one is to grasp the source, to combat the production of fake and shoddy products, the second is to combat the sale of fake and shoddy wire and cable dealers, strict from the heavy treatment; third, the use of fake and shoddy products users to combat education, appropriate punishment. In addition, in the fight against fake and shoddy, but also pay attention to norms, help and guidance, so that enterprises standardize management, improve product quality.

(iii) Supervision and inspection to promote enterprise reform. Strengthen the supervision and inspection of enterprises, improve product quality from the source. At the same time, we should pay more attention to establish quality consciousness and brand consciousness, and make the enterprise change from price war to quality war. In the supervision and inspection, the unqualified products in the punishment at the same time put forward rectification plan, so that the quality of products steadily improve until all qualified.

(iv) to help technological innovation and improve technological content. Encourage enterprises to improve the productivity of labor equipment, improve product quality and technical content, and increase independent research and innovation. For the enterprise to develop revised product standards, so that enterprises to organize production according to standards. Improve the inspection mechanism of enterprises, strengthen the quality control of products, establish a long-term monitoring mechanism. To improve the quality of enterprise awareness, do a good job of enterprise Quality system certification, product quality certification and safety certification.

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