Photovoltaic cables are often exposed to sunlight, and solar systems are often used under harsh environmental conditions, such as high temperature and ultraviolet radiation. In Europe, sunny days will cause the field temperature of the solar system to reach 100°C. At present, we can use various materials including PVC, rubber, TPE and high-quality cross-linking materials, but unfortunately, rubber cables with a rated temperature of 90°C, and even PVC cables with a rated temperature of 70°C It is also often used outdoors. At present, the National Golden Sun Project is frequently launched. In order to save costs, many contractors do not choose special cables for solar systems, but choose ordinary pvc cables to replace photovoltaic cables. Obviously, this will greatly affect the use of the system. life.
The characteristics of photovoltaic cables are determined by their special insulating materials and sheath materials for cables, which we call cross-linked PE. After being irradiated by an irradiation accelerator, the molecular structure of the cable material will change, thereby providing all aspects of its performance. . Resistance to mechanical loads In fact, during installation and maintenance, cables can be routed on the sharp edges of the roof structure, while the cables must withstand pressure, bending, tension, cross tensile loads and strong impacts. If the cable sheath is not strong enough, the cable insulation layer will be severely damaged, which will affect the service life of the entire cable, or cause short-circuit, fire, and personal injury hazards.
Performance of photovoltaic cable
Electrical properties
1. DC resistance
The DC resistance of the conductive core of the finished cable at 20°C is not more than 5.09Ω/km.
2 Immersion voltage test
The finished cable (20m) will not break down after being immersed in (20±5)℃ water for 1h after 5min voltage test (AC 6.5kV or DC 15kV).
3 Long-term DC voltage resistance
The sample is 5m long and put into distilled water containing 3% sodium chloride (NaCl) at (85±2)℃ for (240±2)h, and the two ends are 30cm above the water surface. A DC 0.9kV voltage is applied between the core and the water (the conductive core is connected to the positive electrode, and the water is connected to the negative electrode). After taking out the sample, perform a water immersion voltage test. The test voltage is AC 1kV, and no breakdown is required.
4 Insulation resistance
The insulation resistance of the finished cable at 20℃ is not less than 1014Ω·cm,
The insulation resistance of the finished cable at 90℃ is not less than 1011Ω·cm.
5 Sheath surface resistance
The surface resistance of the finished cable sheath should not be less than 109Ω.
Other properties
1. High temperature pressure test (GB/T 2951.31-2008)
Temperature (140±3)℃, time 240min, k=0.6, the depth of indentation does not exceed 50% of the total thickness of insulation and sheath. And carry out AC6.5kV, 5min voltage test, no breakdown is required.
2 Damp heat test
The sample is placed in an environment with a temperature of 90℃ and a relative humidity of 85% for 1000h. After cooling to room temperature, the change rate of tensile strength is ≤-30% and the change rate of elongation at break is ≤-30% compared with before the test.
3 Acid and alkali resistance test (GB/T 2951.21-2008)
The two groups of samples were immersed in oxalic acid solution with a concentration of 45g/L and sodium hydroxide solution with a concentration of 40g/L, at a temperature of 23°C for 168h. Compared with the solution before immersion, the tensile strength change rate was ≤±30 %, the elongation at break ≥100%.
4 Compatibility test
After the entire cable is aged for 7×24h at (135±2)℃, the change rate of tensile strength before and after insulation aging is ≤±30%, the change rate of elongation at break is ≤±30%; the change rate of tensile strength before and after the sheath is aging is ≤ -30%, change rate of elongation at break ≤±30%.
5 Low temperature impact test (8.5 in GB/T 2951.14-2008)
Cooling temperature -40℃, time 16h, weight of drop weight 1000g, weight of impact block 200g, height of drop 100mm, there should be no visible cracks on the surface.
6 Low temperature bending test (8.2 in GB/T 2951.14-2008)
Cooling temperature (-40±2)℃, time 16h, the diameter of the test rod is 4 to 5 times the outer diameter of the cable, winding 3 to 4 times, after the test, there should be no visible cracks on the sheath surface.
7 Ozone resistance test
The length of the sample is 20cm, and it is placed in a drying vessel for 16h. The diameter of the test rod used in the bending test is (2±0.1) times the outer diameter of the cable. The test chamber: temperature (40±2)℃, relative humidity (55±5)%, ozone concentration (200±50)×10-6% , Air flow: 0.2 to 0.5 times the chamber volume/min. The sample is placed in the test box for 72 hours. After the test, there should be no visible cracks on the sheath surface.
8 Weather resistance
UV test
Each cycle: water spray for 18min, xenon lamp drying for 102min, temperature (65±3) ℃, relative humidity 65%, power under the condition of wavelength 300～400nm: (60±2)W/m2. After 720h, the bending test at room temperature was carried out. The diameter of the test rod is 4 to 5 times the outer diameter of the cable. After the test, there should be no visible cracks on the sheath surface.
9 Dynamic penetration test
At room temperature, the cutting speed is 1N/s, and the number of cutting tests: 4 times. The sample must be moved forward by 25mm and rotated 90° clockwise each time. Record the penetration force F at the moment the spring steel needle contacts the copper wire, and the average value obtained is ≥150·Dn1/2 N (4mm2 section Dn=2.5mm)
10 Dent resistance
Take 3 sections of samples, each section is 25mm apart, and rotate 90° to make a total of 4 dents, the dent depth is 0.05mm and perpendicular to the copper wire. The three sections of samples were placed in a test box at -15°C, room temperature, and +85°C for 3 hours, and then wound on a mandrel in the corresponding test box. The diameter of the mandrel was (3±0.3) times the outer diameter of the cable. At least one score for each sample is located on the outside. It does not break down in the AC0.3kV water immersion voltage test.
11 Sheath thermal shrinkage test (No. 11 in GB/T 2951.13-2008) Cut the sample length L1=300mm, put it in an oven at 120℃ for 1 hour, then take it out to room temperature and cool it down. Repeat this heat and cold cycle 5 times and cool to room temperature. The heat shrinkage rate of the sample is required to be ≤2%.
12 Vertical burning test
After the finished cable is placed at (60±2)℃ for 4 hours, it shall be subjected to the vertical burning test specified in GB/T 18380.12-2008.
13 Halogen content test
PH and conductivity
Sample placement: 16h, temperature (21～25)℃, humidity (45～55)%. Two samples, each (1000±5) mg, crushed to particles below 0.1 mg. Air flow (the distance between the combustion boat and the edge of the furnace heating effective zone is ≥300mm, the temperature at the combustion boat must be ≥935℃, and the temperature 300m away from the combustion boat (in the direction of air flow) must be ≥900℃.
The gas generated by the test sample is collected through a gas washing bottle containing 450ml (PH value 6.5±1.0; conductivity ≤0.5μS/mm) of distilled water. The test period: 30min. Requirements: PH≥4.3; conductivity≤10μS/mm.
Cl and Br content
Sample placement: 16h, temperature (21～25)℃, humidity (45～55)%. Two samples, each (500-1000) mg, crushed to 0.1 mg.
Air flow (0.0157·D2)l·h-1±10%, the sample is uniformly heated for 40min to (800±10)℃, and kept for 20min.
The gas generated by the test sample is sucked by a gas washing bottle containing 220ml/each 0.1M sodium hydroxide solution; the liquid of the two gas washing bottles is injected into the measuring bottle, and distilled water is used to clean the gas washing bottle and its accessories and add to the measuring bottle. 1000ml, after cooling to room temperature, use a straw to drop 200ml of the tested solution into the measuring flask, add 4ml of concentrated nitric acid, 20ml of 0.1M silver nitrate, 3ml of nitrobenzene, then stir until the white flocs are deposited; add 40% ammonium sulfate The aqueous solution and a few drops of nitric acid solution were completely mixed, stirred with a magnetic stirrer, and ammonium sulfite was added to titrate the solution.
Requirements: The average of the test values of the two samples: HCL≤0.5%; HBr≤0.5%;
The test value of each sample ≤ the mean value of the test values of the two samples ± 10%.
F content
Put 25-30 mg of sample material in a 1L oxygen container, drop 2 to 3 drops of alkanol, and add 5 ml of 0.5M sodium hydroxide solution. The sample is burned out, and the residue is poured into a 50ml measuring cup by a slight rinse.
Mix 5ml of buffer with the sample solution and washing solution and reach the mark. Draw a calibration curve, obtain the fluorine concentration of the sample solution, and calculate the percentage of fluorine in the sample.
Requirements: ≤0.1%.
14 Mechanical properties of insulation and sheath materials
Before aging, the tensile strength of the insulation is ≥6.5N/mm2, the elongation at break ≥125%, the tensile strength of the sheath is ≥8.0N/mm2, and the elongation at break ≥125%. After aging at (150±2)℃ for 7×24h, the tensile strength change rate of the insulation and sheath before and after aging is ≤-30%, and the change rate of elongation at break before and after aging of the insulation and sheath is ≤-30%.
15 Hot extension test
Under a load of 20N/cm2, after the sample has been subjected to a thermal extension test at (200±3)℃ for 15min, the median value of the elongation of the insulation and sheath should not be greater than 100%. After the sample is taken out of the oven and cooled, the distance between the marked lines The percentage of the intermediate value of the increase to the distance before the test piece is placed in the oven should not be greater than 25%.
16 Thermal life
According to EN 60
216-1, EN60216-2 Arrhenius curve, the temperature index is 120 ℃. Time is 5000h. Retention rate of insulation and sheath breaking elongation: ≥50%. Then, a bending test at room temperature was performed. The diameter of the test rod is twice the outer diameter of the cable. After the test, there should be no visible cracks on the sheath surface. Required life span: 25 years.
