Electrical performance test
It mainly includes conductor DC resistance, insulation resistance, finished product voltage test and insulated wire core to core voltage test, each of which is very important. The conductor resistance directly reflects the electrical transmission performance of the cable, and directly affects the temperature, life, voltage drop, and operation safety of the cable during energized operation. It mainly checks the material and sectional area of the conductor. If the material of the conductor is poor or the sectional area is seriously insufficient, the conductor DC resistance will seriously exceed the standard, This kind of cable laying in the line will increase the loss when the current passes through the line, cause the cable conductor to heat itself, cause the insulation aging and cracking of the covered conductor, cause the power supply line to leak, short circuit, and even cause fire, endangering the safety of people and property. The standard has strict provisions on the conductor DC resistance of cables of different specifications, which shall not be greater than the value specified in the standard.
The insulation resistance, finished product voltage test and insulated core to core voltage test all examine the electrical insulation performance of the cable insulation layer and sheath layer. The insulation resistance is used to detect the resistance of the insulating material between two conductors, which should be large enough to play an insulation protection role. The finished product voltage test and insulation core to core voltage test not only require the cable to have sufficient insulation capacity, but also require the insulation or sheath material to be uniform without impurities, the thickness to be uniform, and the surface to be free of invisible sand holes, pinholes, etc., otherwise it will cause local breakdown during the withstand voltage test.
Mechanical property test
It is mainly to inspect the tensile strength and elongation at break of plastic materials for insulation and sheath, including before and after aging, as well as the bending test, bending test, load core breaking test, insulation core tear test, static bending test, etc. for finished flexible cables. The tensile strength before and after aging, and the elongation at break before and after aging are the most important and basic indicators of cable insulation and sheath materials. It is required that the materials used for cable insulation and sheath should not only have sufficient tensile strength, but also have certain flexibility.
Aging refers to the ability of insulation and sheath materials to maintain their original performance under high temperature conditions. Aging should not seriously affect the tensile strength and elongation of the materials, which will directly affect the service life of the cable. If the tensile strength and elongation at break are not qualified, the sheath or insulator is likely to break during the construction and installation of the cable, or the sheath and insulation of the cable used in the light and heat environment are likely to become brittle and broken, Expose the live conductor and cause electric shock.
In addition, the flexible cable is not fixed, and there are repeated dragging, bending and other situations in use, so the standard for flexible cables also stipulates that the dynamic bending test, bending test, load core breaking test, insulation core tear test, static bending test and so on should be added to the finished cable to ensure that the cable meets the requirements in actual use. For example, the dynamic bending test is mainly used to check whether the stranded wire of the flexible conductor is broken to reduce the electrical transmission performance or puncture the insulation to reduce the electrical insulation performance when the flexible cable is subjected to external mechanical tensile and bending stresses; It is a test method to determine whether the insulation is deformed or cracked under stress, which affects the electrical insulation performance of cables.
Performance test of insulation and sheath materials
Including thermal weightlessness, thermal shock, high temperature pressure, low temperature bending, low temperature tension, low temperature impact, flame retardancy, etc. These are to check the performance of plastic materials for insulation and sheath. For example, the thermal weight-loss test is to check the degree of material degradation and volatilization after 7 days of high temperature aging at 80 ℃; Thermal shock test shall be conducted to check whether there is crack on the insulation surface after special winding at 150 ℃ for 1h; High temperature pressure is used to detect the elasticity of insulating materials after high temperature and cooling; All low temperature tests generally refer to the change of mechanical properties under the condition of - 15 ℃, which are used to detect whether the cable materials are brittle, easy to crack or easy to break under the low temperature environment. In addition, the flame-retardant performance of cables is very important. The test to examine this performance is the non delayed burning test, that is, the finished cables installed according to the standard are ignited with a special flame for a certain period of time. After the flame extinguishes itself, the burning condition of the cables is checked. Of course, the fewer the burned parts, the better, which indicates that their flammability is poor, flame-retardant and safer.
Sign inspection
The standard requires that the cable package shall be attached with labels or signs indicating the product model, specification, standard number, manufacturer name and place of origin, and the specifications include rated voltage, number of cores, nominal cross-section of conductor, etc; The cable surface shall be printed with continuous signs of the manufacturer's name, product model and rated voltage. The distance between the signs shall be ≤ 200mm (insulation surface) or ≤ 500mm (sheath surface). The contents of the signs shall be complete, clear and scratch resistant. This requirement is to facilitate users to understand the cable model, specification and voltage level to prevent wrong laying.
In addition, the color recommended in the standard shall be preferred for the insulated wire core of the wire, especially the yellow/green two-color wire core, which is generally used in the power line of electrical products. This special two-color wire is specially used for grounding. The yellow/green matching standard also has the following provisions: that is, for each length of two-color insulated wire core, one color shall cover at least 30% of the surface of the insulated wire core, and not more than 70%, The other color covers the rest of the insulated core, that is, the yellow/green color should be basically balanced.
Structural dimension inspection
Including the thickness, thinnest thickness and overall dimensions of insulation and sheath. The thickness of insulation and sheath plays an important role in how strong the cable can withstand the voltage and its mechanical performance. Therefore, for cables of different specifications, the standards have strict provisions on the thickness, which shall not be lower than the specified value of the national standard. The thin insulation thickness of the cable will seriously affect the safety of the cable, and will bring potential safety hazards such as cable breakdown and leakage caused by exposed conductors. Of course, the thicker the insulation thickness is, the better it is. It should not affect the installation. Therefore, the standard has set a dimension requirement to limit this.
