According to the relevant provisions of national standards, Wire Cable's testing projects mainly include two aspects of electrical performance and mechanical performance. Among them, electrical performance testing mainly includes DC resistance detection, insulation resistance detection and power frequency withstand voltage detection.
(1) DC resistance detection.
There is a clear definition in the relevant national standards: the DC resistance of the Wire Cable
shall be based on the conductor resistance per kilometer as the reference for comparison. The measured DC resistance data of the Wire Cable must first be converted to a temperature of 20 ° C per kilometer. DC resistance value. If the measured DC resistance value is converted to the DC resistance value under the condition of 20 ° C, if the value is less than the specified standard value, then the Wire Cable sample is a qualified product, and vice versa is a non-conforming product.
At present, the relevant domestic departments usually use the bridge method and the current method to determine the DC resistance of the Wire Cable. The bridge method has a narrow measurement range and can be divided into a single arm bridge method and a double arm bridge method. When the resistance value of the Wire Cable is about 1 or more, the single arm bridge method is used; when the Wire Cable resistance value is less than 1, The double-arm bridge method is used. The current method, also known as the micro-ohmmeter method, is based on the value of the Wire Cable resistance, using a constant current source to output different constant currents, and then accurately measuring the voltage across the measured Cable Cable. The measured data is in accordance with Ohm's law. The DC resistance of the measured Wire Cable can be calculated. The current method can output different currents, so the measurement range is relatively wide.
(2) Insulation resistance detection.
The insulation resistance measurement of Wire Cable must be converted to the insulation resistance value per kilometer. Unlike the DC resistance, the insulation resistance value is inversely proportional to the length of the Wire Cable; the measured voltage of the low-voltage Wire Cable insulation resistance is 100V. There are four kinds of 250V, 500V and 1000V. The detection voltages of 100V and 500V are widely used in the inspection by the quality inspection department. The length of the measured Cable Cable is not specified, but for measurement and calculation, it is generally taken 10m. The charging time before measurement is generally 1 minute.
Wire Cable's insulation resistance test generally uses the voltage and current method, also known as the high resistance meter method. Some Wire Cables have a metal protective cover with a certain shielding function. For the insulation resistance measurement of this Wire Cable, the insulation resistance between the conductor and the metal sleeve or the shielding layer or the armor layer is mostly measured; and for the metal-free sheath. Wire Cable, when measuring the insulation resistance value, must first immerse the measured Wire Cable i
n water, and then measure the insulation resistance between the conductor and the water, and the test sample should be kept in line with the water temperature.
At present, a DC resistance insulation resistance tester ZZJ3D has been developed in China. The tester is easy to operate, and the whole process of measurement can be controlled by computer. The accuracy and stability are much higher than the traditional detection equipment.
(3) Power frequency withstand voltage detection.
The power frequency withstand voltage is generally detected by using an alternating voltage. The national standard stipulates that the AC voltage used is an approximate sine wave with a frequency between 49 Hz and 61 Hz. For a product with a rated voltage of 450/750 V for Wire Cable, a high voltage of 1500 V is used when the insulation thickness is mm 0.6 mm; when the insulation thickness is ≧ 0.6 mm Use 2000V high voltage, pressurize for 5 minutes, if the measured Wire Cable sample does not break down or flashover is qualified product, and vice versa. For example, if a sample with a size of 60227 IEC53 (RVV) 300/500V32.5 needs to withstand pressure, then we need to connect the first core to the high pressure water, then the second core to the high pressure water, and then the third core. Connect the high pressure to the water, and finally need all 3 cores to connect the high pressure to the water for 1 time, and a total of 4 times of pressure.
(4) Mechanical performance testing.
Mechanical properties mainly refer to the tensile strength of the Wire Cable before and after aging. Relevant national standards stipulate that the aging Wire Cable specimens are prepared using a forced air aging chamber, and the sampling should be as close as possible to the unaged portion. The detection of mechanical properties is generally carried out directly using an electronic tensile measuring instrument. Firstly measure the width and thickness of the middle part of the measured Cable Cable with a thickness gauge, then manually aging the sample in a blast drying oven, and then measuring with an electronic tensile machine to record the elongation of the Wire Cable tensile fracture. The distance and the maximum tensile stress can be used to calculate the tensile strength and elongation at break of the measured Wire Cable before and after aging, and the product standard can be compared to the product standard.
(5) Other testing items and testing methods.
In addition to the above-mentioned main test items, there are also items such as the detection of insulation thickness, the detection of dimensions and marks, and the detection of the thickness of the sheath. These can generally be performed by some simple measuring instruments or manual inspection. The thickness of the insulation refers to the thickness after removing all the protective layers on the insulating layer. It is measured by a projector and a reading microscope. After the measurement data is averaged, it is compared with the product standard. The average value must be greater than the specified value to be qualified. product. The external dimensions can be measured with a projector or a wrap. The ellipticity is measured by measuring the outer diameter of any two points on the same cross-section of the circular sheathed cable, taking the difference, and then using the difference and the cable standard to specify the average. The outer diameter ratio cannot exceed 15%. China's Wire Cable logo has a high failure rate. The national standard stipulates that the Wire Cable
logo must have continuity and rub resistance, and has high definition. The rubbing resistance needs to be gently rubbed with medical absorbent cotton. Wipe back and forth 10 times, and the printing is clear.