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| The rapid development of power industry is an important guarantee for the economic development of a country, and wires and cables are indispensable products in the process of power construction. At present, China's wire and cable industry has jumped to the first manufacturing country. But the quality problem in the domestic wire and cable is also prominent, It is often seen. the fire, or other accidents worrying, in the production process according to the national standard, on the basis of the scientific method, to improve the detection of each project, to provide scientific and accurate basis for strengthening supervision. At present, the domestic wire and cable manufacturers and messy, production technology level is uneven, the industry quality assurance system is not perfect, cause there is a big gap between China's production of wire and cable products quality and other developed countries. In addition, some manufacturers for the pursuit of high profits, the use of substandard raw materials and production processes, further lead to shoddy wire and cable products flooded the domestic market. In recent years, the wire and cable detection problem countries have gradually pay attention to it, and make some strict production and quality, to a certain extent, promote China's wire and cable products to improve the quality of. Performance issues A quality inspection institutions at home had on the electric wire and cable have been investigated and results show that the ISO9000 certified production enterprise, the cable can pass rate is below 90%, while those who did not pass the certification of small scale wire and cable production enterprises, the product qualification rate even reached less than 30%. According to a survey report issued by the quality inspection agencies, wire and cable franchise stores on the market sales, the overall pass rate of around 70% in general, the smaller the hardware store, the qualified rate of its sales of wire and cable even reach 10%. Domestic wire and cable quality is worrying. test method According to the relevant provisions of national standards, test items include cable detection in two aspects of the electrical and mechanical properties, the electrical properties of the main test DC resistance testing, insulation resistance detection and detection of the power frequency withstand voltage. (1) DC resistance measurement. There are clear provisions of the relevant national standards: DC resistance wire and cable to conductor resistance per kilometer as benchmarks, the DC resistance of the measured data of the cable must be first converted into DC resistance per kilometer 20 temperature value. When the measured DC resistance value is converted to the DC resistance value at 20 degrees centigrade, if the value is less than the standard value, the sample of the wire and cable is a qualified product, otherwise it is a nonconforming product. At present, two methods of bridge method and current method are usually used to determine the DC resistance of wire and cable. The measuring range was relatively narrow, can be divided into Wheatstone bridge method and double bridge method, when the resistance wire and cable is about 1 more than using Wheatstone bridge method; double bridge method is used when the cable resistance value is less than 1. The current method is also called micro ohm meter method, it is based on the principle of wire and cable resistance values, using constant current source output constant current is different, and then measuring the voltage being measured at both ends of the wire cable accurately, the measured data in accordance with the DC resistance of Ohm's law can be obtained by measuring operation of wire and cable. Current method can output different currents, so its measurement range is relatively wide. (two) insulation resistance test. Measuring insulation resistance of wire and cable insulation resistance value must be converted into value per kilometer, and the DC resistance is different, the value of insulation resistance and inversely proportional to the length of wire and cable; insulation resistance measuring voltage when detecting the voltage wires and cables are 100V, 250V, 500V and 1000V four, the detection voltage 100V and 500V in the quality inspection department is widely used; the measured cable length, but in order to facilitate the measurement and calculation, generally 10m measurement. The charge time before the measurement is usually 1 minutes. The method of voltage and current is also used to detect the insulation resistance of wires and cables, which is also called high impedance method. Some wires and cables with metal protective sleeve, a shielding function, for measuring insulation resistance measurement of metal conductor mostly or shielding layer or layer between the insulation resistance of the armored cables; and for wire and cable metal sheath, measuring the insulation resistance value, must first be measured by wire and cable immersed in water then, to measure the insulation resistance between the conductor and the water, and the detection of the tested sample shall be kept and water facilities. A DC resistance insulation resistance tester ZZJ3D has been developed in China. The tester is easy to operate, and the measurement process can be controlled by computer. The accuracy and stability of the tester are much higher than the traditional testing equipment. (three) power frequency withstand voltage test. Power frequency withstand voltage is generally detected by AC voltage. National standard: the AC voltage frequency for approximate sine wave in 49Hz ~ 61Hz; the rated voltage is 450/750V for wire and cable products, when the insulation thickness is less than or equal to 0.6mm when using the 1500V high pressure; when the insulation thickness is not less than 0.6mm by 2000V pressure, the pressure for 5 minutes, if the measured cable samples no breakdown or flashover is the qualified product, otherwise unqualified. For example, a specification for 60227IEC53 (RVV) 300/500V32.5 samples to pressure, then we will put first core high pressure on water, then the second core is connected with a high pressure on water, and then the third core is connected with a high pressure on water, finally all 3 of the core is connected with the high-pressure water 1 times the total pressure. |
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