Sharing this information with colleagues in the industry about the introduction and selection of photovoltaic cables for reference.
I. Types, Characteristics, and Installation Methods of Photovoltaic Power Generation System Cables
Main types of photovoltaic power generation system cables include:
PV-specific cables, power cables, control cables, communication cables, and radio frequency cables
PV-specific cables: PV1-F 1*4mm²
The cables connecting the string to the combiner box are generally: PV-specific cables PV1-F 1*4mm².
Features: PV cables have a simple structure. The polyolefin insulation material used is extremely resistant to heat, cold, oil, and UV rays, making them suitable for use in harsh environments and possessing a certain degree of mechanical strength.
Installation: They can be routed in conduits for protection, with module brackets serving as a channel and anchor for cable installation to minimize the impact of environmental factors.
Power cable: ZRC-YJV22
Steel belt armored flame retardant cross-linked cable ZRC-YJV22 is widely used in: connecting cables from junction box to DC cabinet, DC cabinet to inverter, inverter to transformer, transformer to distribution device, and distribution device to grid.
The more common nominal cross-sections of ZRC-YJV22 cables in photovoltaic power generation systems are: 2.5mm², 4mm², 6mm², 10mm², 16mm², 25mm², 35mm², 50mm², 70mm², 95mm², 120mm², 150mm², 185mm², 240mm², 300mm².
Features:
(1) Hard texture, temperature resistance grade 90℃, easy to use, with low dielectric loss, chemical corrosion resistance and installation without drop restrictions.
(2) High mechanical strength, good resistance to environmental stress, good thermal aging performance and electrical properties. Installation: Suitable for direct burial and fixed installation, adapting to various installation environments (underground, underwater, in trenches, and tunnels).
Power Cable: NH-VV
NH-VV copper-core PVC insulated, PVC sheathed, fire-resistant power cable. Suitable for rated voltages of 0.6/1 kV.
Performance: Permissible long-term operating temperature: 80°C. Permissible bending radius during installation: No less than 20 times the cable's outer diameter for single-core cables and no less than 12 times the cable's outer diameter for multi-core cables. No preheating is required, provided the ambient temperature during installation is at least 0°C. Voltage installation is not subject to drop restrictions.
Installation: Suitable for applications requiring fire resistance, suitable for indoor installation, tunnels, and trenches. Note that it cannot withstand mechanical forces and can be installed directly underground.
Control Cable: ZRC-KVVP
ZRC-KVVP copper-core PVC insulated, PVC sheathed, braided shielded control cable. Suitable for control, monitoring, and protection circuits with AC rated voltages of 450/750V and below.
Features: Permissible long-term operating temperature: 70°C. Minimum bending radius: 6 times the cable's outer diameter.
Installation: Generally installed indoors, in cable trenches, ducts, and other fixed locations requiring shielding and flame retardancy.
Communication Cable: DJYVRP2-22
DJYVRP2-22 polyethylene-insulated, PVC-sheathed, copper-wire braided shielded, armored computer-specific flexible cable is suitable for electronic computers and automation connection cables with rated voltages of 500V and below, requiring high interference protection.
Features: DJYVRP2-22 cable features oxidation resistance, high insulation resistance, excellent voltage resistance, and a low dielectric constant. While ensuring long service life, it also reduces crosstalk and external interference between circuits, ensuring high signal transmission quality. Minimum bending radius: 12 times the cable's outer diameter.
Installation: The cable can be used in fixed installations in ambient temperatures between -40°C and 50°C. For installation indoors, in cable trenches, ducts, and other locations requiring electrostatic shielding.
Communication Cable: RVVP
Copper-core PVC-insulated, PVC-sheathed, shielded flexible cable (RVVP), also known as electrical connection anti-interference flexible cable, is suitable for applications such as alarms and security that require interference prevention and ensure safe and efficient data transmission.
Features: Rated operating voltage 3.6/6kV, cable conductor long-term operating temperature 90°C, minimum allowable bend radius 6 times the cable's outer diameter. Primarily used as a communication cable, it provides interference resistance. Installation: RVVP cable should not be exposed to sunlight, and the lower conductor must be well grounded. For weak-current circuit communication cables requiring electrical interference suppression, they should be installed in steel pipes or boxes. When installed parallel to power cables, the spacing should be as far as possible.
RF Cable: SYV
Solid-core polyethylene-insulated, PVC-sheathed RF coaxial cable (SYV)
Features: The two most commonly used video cables for surveillance are SYV75-3 and SYV75-5. If you need to transmit video signals within 200 meters, use the SYV75-3; if you need to transmit signals within 350 meters, use the SYV75-5.
Installation: Can be laid in conduit.
2. PV Cable Selection and Calculation
The cable cross-section should meet requirements for allowable temperature rise, voltage loss, and mechanical strength. For DC systems, cables should be selected based on their long-term allowable current carrying capacity and verified based on their allowable voltage drop. The calculation formula is as follows:
Based on the long-term allowable current carrying capacity of the cable: Ipc >= Ical
Based on the allowable voltage drop of the circuit: Scac = P·2LIca/△Up
Where: Ipc = allowable current carrying capacity of the cable, A; Ica = calculated current, A; Ical = calculated long-term operating current of the circuit, A; Scac = calculated cable cross-section, mm²; P = resistivity (P = 0.0184 Ω·mm²/m for copper conductors and 0.0315 Ω·mm²/m for aluminum conductors); L = cable length, m; △Up = allowable voltage drop of the circuit, V.
Note: The current carrying capacity of a cable is significantly affected by the installation method and surrounding environment, while the voltage drop of a cable is significantly affected by its length. Therefore, the current carrying capacity should be considered a value that should never be exceeded during long-term operation. It is best to select cables that meet 70%-80% of the current carrying capacity to effectively minimize line temperature rise and voltage drop.
III. Relevant Standards and Specifications Related to Cable Selection
1. DL/T 5044-2004 Electric Power Industry Standard of the People's Republic of China
When selecting multi-core cables, their allowable current carrying capacity can be calculated based on the value for single-core cables of the same cross-section.
Control and signal lines leading from the DC cabinet should be copper-core cables. Their voltage drop should not exceed 5% of the nominal voltage of the DC system.
The selection and installation of DC cables should comply with the relevant provisions of GB 50217.
2. GB 50217 Design Specification for Power Engineering Cables
Two-core cables are preferred for DC power supply circuits; single-core cables may be used when necessary.
PVC insulated cables should not be used in places with high temperatures (above 100°C) or low temperatures (below -20°C). When laying cables directly underground, steel-belt armored cables should be used when the cables are under great pressure or are in danger of mechanical damage. The cable core temperature under the action of the maximum working current shall not exceed the allowable value determined according to the service life of the cable. The ambient temperature for determining the continuous allowable current carrying capacity of the cable shall be the average of the highest temperatures of the hottest day in the hottest month if the cable is laid in the air or in a cable trench. 3. The selection of cable routes shall comply with the following provisions: (1) Avoid the cable from being subjected to mechanical external forces, overheating, corrosion and other hazards. (2) Keep the cable shorter while meeting safety requirements. (3) Facilitate laying and maintenance. (4) Avoid places where excavation and construction will be carried out. (5) The cable shall meet the allowable bending radius requirements for any up and down, left and right changing parts of the cable in any laying method and all path conditions.
