Solar energy technology will become one of the green energy technologies in the future. Solar energy or photovoltaic (PV) is widely used in China. In addition to the rapid development of government-supported photovoltaic power plants, private investors are also actively building plants and plan to put them into production for global sales. Solar modules.

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 various 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-tension 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.

Main performance

一、Electrical performance

1. DC resistance

The DC resistance of the conductive core of the finished cable at 20℃ is not more than 5.09Ω/km.

2 Immersion voltage test

The finished cable (20m) will not breakdown after being immersed in (20±5)℃ water for 1h after 5min voltage test (AC 6.5kV or DC 15kV).

3 Long-term withstand DC voltage

The sample is 5m long and put into distilled water containing 3% sodium chloride (NaCl) at (85±2)℃ for (240±2)h, with both ends exposed to the water surface by 750px. 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.

二、Performance test

1. High temperature pressure test (GB/T 2951.31-2008)

Temperature (140±3)℃, time 240min, k=0.6, indentation depth does not exceed 50% of the total thickness of insulation and sheath. And carry on AC6.5kV, 5min voltage test, require no breakdown.

2. Damp heat test

The sample is placed in an environment with a temperature of 90℃ and a relative humidity of 85% for 1000 hours. After cooling to room temperature, the change rate of tensile strength is ≤-30%, and the change rate of elongation at break is ≤-30%.

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℃ 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 cable as a whole is aged at (135±2)℃ for 7×24h, 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 aged ≤ -30%, change rate of elongation at break ≤±30%.

5. Low temperature impact test (8.5 in GB/T 2951.14-2008)

Cooling temperature is -40℃, time is 16h, weight of drop hammer is 1000g, mass of impact block is 200g, height of drop is 100mm, and 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, there should be no visible cracks on the sheath surface after the test.

7. Ozone resistance test

The length of the sample is 500px, and it is placed in a drying vessel for 16 hours. 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: 0.2-0.5 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%, minimum power under the condition of wavelength 300～400nm: (60±2)W/m2. After 720 hours, a 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. Each time you continue the test, the sample must be moved forward by 25mm and rotated 90° clockwise. 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 resistant

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 is 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 each corresponding test box. The diameter of the mandrel was (3±0.3) times the minimum 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)

The cut length of the sample is L1=300mm, placed in an oven at 120℃ for 1h, and then taken out to room temperature to cool. Repeat this cooling and heating cycle 5 times, and finally cooling to room temperature. The thermal shrinkage 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

(1) 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 (0.0157·D2)l·h-1±10%, the distance between the combustion boat and the edge of the effective heating zone of the furnace is ≥300mm, the temperature at the combustion boat must be ≥935℃, 300m away from the combustion boat (in the direction of air flow ) The temperature 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.

The content of important elements

(2) Cl and Br content

Sample placement: 16h, temperature (21～25)℃, humidity (45～55)%. Two samples, each (500-1000) mg, crushed to 0.1 mg.

The air flow rate is (0.0157·D2)l·h-1±10%, and 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 inject the measuring bottle to 1000ml, after cooling to room temperature, use a straw to drop 200ml of the tested solution into the measuring flask, add 4ml concentrated nitric acid, 20ml 0.1M silver nitrate, 3ml nitrobenzene, and then stir until white flocs deposit; 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 sulfate 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%.

(3) 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 gentle flushing.

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)℃ and 7×24h, the change rate of tensile strength before and after aging of the insulation and sheath 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 is subjected to a thermal extension test at (200±3)℃ for 15min, the median value of the elongation of the insulation and sheath should not exceed 100%. The test piece is taken out of the oven and cooled, and the distance between the marked lines The intermediate value of the increase in the percentage of the distance before the test piece is placed in the oven should not be greater than 25%.

16. Thermal life

According to EN 60216-1, EN60216-2 Arrhenius curve, the temperature index is 120℃. Time 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 lifespan: 25 years.

三、Cable selection

The cables used in the low-voltage DC transmission part of the solar photovoltaic power generation system have different requirements for the connection of different components because of the different use environment and technical requirements. The overall factors to be considered are: the insulation performance of the cable, the heat-resistant and flame-retardant performance, Engage in aging performance and wire diameter specifications. Specific requirements are as follows:

1. The connecting cable between the solar cell module and the module is generally connected directly with the connecting cable attached to the module junction box. When the length is not enough, a special extension cable can be used. Depending on the power of the components, this type of connecting cable has three specifications: 2.5 mm2, 4.0 mm2, and 6.0 mm2. This type of connecting cable uses double-layer insulation, which has superior anti-ultraviolet, water, ozone, acid, and salt corrosion resistance, superior all-weather capability and wear resistance.

2. The connecting cable between the battery and the inverter requires the use of a multi-strand flexible wire that has passed the UL test and should be connected as close as possible. Choosing a short and thick cable can reduce the loss of the system, improve efficiency, and enhance reliability.

3. The connection cable between the battery square array and the controller or DC junction box also requires the use of multiple strands of flexible wires that have passed the UL test. The cross-sectional area specification is determined by the maximum current output of the square array.

The cross-sectional area of the DC cable at the designated part is determined according to the following principles: The connecting cable between solar cell modules and the module, the connecting cable between the storage battery and the storage battery, and the connecting cable of the AC load. Generally, the rated current of the selected cable is the maximum continuous operation of each cable 1.25 times the current; the connecting cable between the solar cell array and the array, the connecting cable between the battery (group) and the inverter, the rated current of the cable generally selected is 1.5 times the maximum continuous working current in each cable.

四、Export certification

For photovoltaic cables supporting other photovoltaic modules exported to Europe, the cables must comply with the TUV MARK certificate issued by TUV Rheinland, Germany. At the end of 2012, TUV Rheinland Germany introduced a series of new standards supporting photovoltaic modules, 1.5KV DC single-core wire and photovoltaic AC multi-core wire.