To share with colleagues in the industry the performance requirements for photovoltaic cables, this article lists 16 comprehensive electrical, temperature resistance, and mechanical performance requirements.
1. DC resistance: The DC resistance of the conductive core of the finished cable at 20°C shall not exceed 5.09Ω/km.
2. Water immersion voltage test: After immersing the finished cable (20m) in (20±5)°C water for 1 hour, undergo a 5-minute voltage test (AC 6.5kV or DC 15kV) and no breakdown is observed.
3. Long-term DC voltage resistance: A 5m long sample is immersed in distilled water containing 3% sodium chloride (NaCl) at (85±2)°C for 240±2 hours, with both ends exposed 30cm above the water surface. A DC voltage of 0.9kV is applied between the cable core and the water (the conductive core is connected to the positive terminal and the water is connected to the negative terminal). After removing the sample, a water immersion voltage test is performed at an AC voltage of 1kV, with no breakdown.
4. Insulation Resistance: The insulation resistance of the finished cable at 20°C shall be no less than 1014Ω•cm. The insulation resistance of the finished cable at 90°C shall be no less than 1011Ω•cm.
5. Sheath Surface Resistance: The surface resistance of the finished cable sheath shall be no less than 109Ω. Other Performance 1. High-Temperature Pressure Test (GB/T2951.31-2008): Temperature (140±3)°C, time (240 min), k=0.6, indentation depth shall not exceed 50% of the total thickness of the insulation and sheath. An AC 6.5kV, 5 min voltage test shall also be conducted, with no breakdown.
2. Damp Heat Test: The sample shall be placed in an environment with a temperature of 90°C and a relative humidity of 85% for 1000 hours. After cooling to room temperature, the change in tensile strength shall be ≤-30%, and the change in elongation at break shall be ≤-30% compared to before the test.
3. Acid and Alkali Solution Resistance Test (GB/T2951.21-2008)
Two groups of samples were immersed in 45g/L oxalic acid solution and 40g/L sodium hydroxide solution, respectively, at 23°C for 168 hours. Compared with the pre-immersion period, the change in tensile strength was ≤±30%, and the elongation at break was ≥100%.
4. Compatibility Test
After aging the entire cable for 7×24 hours at (135±2)°C, the change in tensile strength of the insulation before and after aging was ≤±30%, and the change in elongation at break was ≤±30%. The change in tensile strength of the sheath before and after aging was ≤-30%, and the change in elongation at break was ≤±30%.
5 Low-Temperature Impact Test (8.5 of GB/T2951.14-2008)
Cooling temperature: -40°C, duration: 16 hours, drop weight: 1000g, impact block: 200g, drop height: 100mm. No visible cracks should be observed on the surface.
6 Low-Temperature Bend Test (8.2 of GB/T2951.14-2008)
Cooling temperature: (-40±2)°C, duration: 16 hours, test rod diameter: 4-5 times the cable outer diameter, wrapped 3-4 times. After the test, no visible cracks should be observed on the sheath surface.
7 Ozone Resistance Test
Specimen length: 20cm, placed in a desiccating container for 16 hours. The test rod diameter for the bend test is (2 ± 0.1) times the cable's outer diameter. The test chamber temperature is (40 ± 2)°C, relative humidity is (55 ± 5)%, ozone concentration is (200 ± 50) × 10-6%, and air flow is 0.2–0.5 times the chamber volume/min. The sample is placed in the test chamber for 72 hours. After the test, no visible cracks should be observed on the sheath surface.
8. Weather Resistance/UV Test
Each cycle consists of 18 minutes of water spraying and 102 minutes of xenon lamp drying. The test chamber temperature is (65 ± 3)°C, relative humidity is 65%, and the minimum power at a wavelength of 300–400 nm is (60 ± 2) W/m². After 720 hours of continuous operation, a bend test is conducted at room temperature. The test rod diameter is 4–5 times the cable's outer diameter. After the test, no visible cracks should be observed on the sheath surface.
9. Dynamic Penetration Test
At room temperature, cut at a speed of 1 N/s. Four cutting tests were performed. Each time the sample was moved forward 25 mm and rotated 90° clockwise, the test was repeated. The penetration force F at the moment the spring steel needle made contact with the copper wire was recorded. The average value was ≥ 150•Dn1/2N (for a 4 mm2 cross-section, Dn = 2.5 mm).
10. Dent Resistance
Three samples were taken. Four indentations were made on each sample, 25 mm apart and rotated 90°. The indentations were 0.05 mm deep and perpendicular to the copper conductor. The three samples were placed in test chambers at -15°C, room temperature, and +85°C for 3 hours. The samples were then wound around a mandrel in their respective chambers. The mandrel diameter was (3 ± 0.3) times the minimum outer diameter of the cable. At least one indentation on each sample was located on the outside. No breakdown was observed during an AC 0.3 kV water immersion test.
11. Sheath Thermal Shrinkage Test (11 in GB/T2951.13-2008)
Cut the sample to a length of L1 = 300mm and place it in a 120°C oven for 1 hour, then remove it and cool it to room temperature. Repeat this hot and cold cycle five times before finally cooling it to room temperature. The sample thermal shrinkage must be ≤2%.
12. Vertical Flame Test
After the finished cable is placed at (60±2)°C for 4 hours, it is subjected to the vertical flame test specified in GB/T18380.12-2008.
13. Halogen Content Test: pH and Conductivity
Samples are placed for 16 hours at a temperature of (21-25)°C and a humidity of (45-55)%. Two samples, each weighing (1000±5)mg, are crushed to particles less than 0.1mg. Air flow rate: (0.0157·D2) l·h-1 ± 10%. The distance between the combustion boat and the edge of the furnace's active heating zone must be ≥ 300mm. The temperature at the combustion boat must be ≥ 935°C, and the temperature at 300m from the combustion boat (in the direction of air flow) must be ≥ 900°C.
The gas generated by the test sample is collected in a gas wash bottle containing 450ml of distilled water (pH 6.5±1.0; conductivity ≤ 0.5μS/mm). Test period: 30min. Requirements: pH ≥ 4.3; conductivity ≤ 10μS/mm.
Cl and Br content
Sample storage: 16h, temperature (21-25)°C, humidity (45-55)%. Two samples, each weighing (500-1000)mg, are crushed to 0.1mg.
The air flow rate was (0.0157·D2) l·h-1 ± 10%. The sample was uniformly heated for 40 minutes to (800±10)°C and maintained for 20 minutes.
The gas generated by the test sample was drawn through a gas wash bottle containing 220ml of 0.1M sodium hydroxide solution. The liquid from the two gas wash bottles was poured into a volumetric flask. The gas wash bottles and accessories were rinsed with distilled water and then added to the volumetric flask to 1000ml. After cooling to room temperature, 200ml of the test solution was pipetted into the volumetric flask. 4ml of concentrated nitric acid, 20ml of 0.1M silver nitrate, and 3ml of nitrobenzene were added and stirred until white flocs were deposited. 40% ammonium sulfate aqueous solution and a few drops of nitric acid solution were added and mixed thoroughly. Stirring was performed with a magnetic stirrer, and ammonium bisulfate titration solution was added.
Requirements: Average of the test values of the two samples: HCL ≤ 0.5%; HBr ≤ 0.5%;
The test value of each sample was ≤ the average of the two sample values ± 10%.
F Content
Place 25-30 mg of sample material in a 1 L oxygen container, add 2-3 drops of alkanol, and add 5 ml of 0.5 M sodium hydroxide solution. Allow the sample to burn completely, then gently rinse the residue into a 50 ml measuring cup.
Mix 5 ml of buffer with the sample solution and rinse solution until the concentration reaches the mark. Draw a calibration curve to determine the fluorine concentration of the sample solution, and calculate the percentage of fluorine in the sample.
Requirement: ≤ 0.1%.
14 Mechanical Properties of Insulation and Sheath Materials
Before aging, the insulation tensile strength must be ≥ 6.5 N/mm², and the elongation at break must be ≥ 125%. The sheath tensile strength must be ≥ 8.0 N/mm², and the elongation at break must be ≥ 125%.
After aging at (150 ± 2)°C for 7 x 24 hours, the change in tensile strength of the insulation and sheath before and after aging must be ≤ -30%, and the change in elongation at break of the insulation and sheath before and after aging must be ≤ -30%.
15. Thermal Elongation Test
After a thermal elongation test at (200±3)°C for 15 minutes under a load of 20 N/cm², the median value of the insulation and sheath elongation should be no greater than 100%. The median value of the increase in the distance between the marked lines after the specimen is removed from the oven and cooled should be no greater than 25% of the distance before the specimen was placed in the oven.
16. Thermal Life
This test is conducted according to the Arrhenius curve of EN60216-1 and EN60216-2, with a temperature index of 120°C. The test duration is 5000 hours. Retention of elongation at break of the insulation and sheath: ≥50%. A room temperature bend test is then conducted. The test rod diameter is twice the cable's outer diameter. After the test, no visible cracks should be observed on the sheath surface. Required lifespan: 25 years.
