According to the system of photovoltaic power plants, cables can be divided into DC cables and AC cables. According to different purposes and usage environments, they are classified as follows:DC cable
(1) Tandem cables between components.
(2) Parallel cables between strings and between strings and DC distribution boxes (combiner boxes).
(3) Cable from DC distribution box to inverter.
The above cables are all DC cables, which are often laid outdoors and require moisture resistance, exposure to sunlight, cold resistance, heat resistance, and UV resistance. In some special environments, they also need to be resistant to chemicals such as acid and alkali.
AC cable
(1) The connecting cable from the inverter to the step-up transformer.
(2) Connection cable from step-up transformer to distribution device.
(3) The connecting cable from the power distribution device to the power grid or users.
This part of the cable is an AC load cable, which is commonly laid in indoor environments. It can be selected according to general power cable selection requirements.
Solar cables
A large number of DC cables in photovoltaic power plants need to be laid outdoors, and the environmental conditions are harsh. The cable materials should be determined based on their resistance to UV, ozone, severe temperature changes, and chemical erosion. Long term use of ordinary material cables in this environment will cause the cable sheath to be fragile and even decompose the cable insulation layer. These situations can directly damage the cable system and increase the risk of cable short circuits. In the medium to long term, the likelihood of fire or personal injury is also higher, greatly affecting the service life of the system.
Therefore, it is very necessary to use photovoltaic specialized cables and components in photovoltaic power plants. With the continuous development of the photovoltaic industry, the market for photovoltaic supporting components has gradually formed. In terms of cables, various specifications of photovoltaic professional cable products have been developed. The recently developed electron beam cross link cable has a rated temperature of 120 ℃, which can withstand harsh climatic environment and mechanical shock. For example, RADOX cable is a solar specialized cable developed according to the international standard IEC216. In outdoor environments, its service life is 8 times that of rubber cables and 32 times that of PVC cables. Photovoltaic specialized cables and components not only have the best weather resistance, UV resistance, and ozone erosion resistance, but also can withstand a larger range of temperature changes (such as from -40 to 125 ℃). In Europe, technicians have tested and found that the temperature values measured on the roof can reach as high as 100-110 ℃.
Cable conductor material
The DC cables used in photovoltaic power plants are mostly for long-term outdoor work, and due to construction conditions, cable connections are mostly made using connectors. Cable conductor materials can be divided into copper core and aluminum core. Copper core cables have the characteristics of better oxidation resistance, longer lifespan, better stability, low voltage drop, and low power loss compared to aluminum; In construction, due to the good flexibility of the copper core and the small allowable bending radius, it is easy to turn and thread the pipe; Moreover, the copper core is resistant to fatigue and is not easily broken after repeated bending, making wiring convenient; At the same time, the mechanical strength of the copper core is high, which can withstand large mechanical tensile forces, bringing great convenience to construction and laying, and also creating conditions for mechanized construction. On the contrary, aluminum core cables are prone to oxidation (electrochemical reaction) during installation due to the chemical properties of aluminum materials, especially creep, which can lead to faults.
Therefore, copper cables have outstanding advantages in the use of photovoltaic power stations, especially in the field of direct buried cable power supply. It can reduce accident rates, improve power supply reliability, and facilitate construction, operation, and maintenance. This is precisely the reason why copper cables are currently mainly used in underground cable power supply in China.
Cable insulation and sheath materials
During the installation, operation and maintenance of photovoltaic power plants, cables may be laid in soil below the ground, in weeds and rocks, on sharp edges of roof structures, or exposed to the air. The cables may withstand various external forces. If the strength of the cable sheath is insufficient, the insulation layer of the cable will be damaged, which will affect the entire service life of the cable, or lead to problems such as short circuits, fire, and danger of personal injury. Cable researchers and technicians have found that materials that have been cross-linked by radiation have higher mechanical strength than before radiation treatment. The cross linking process has changed the chemical structure of the polymer used in cable insulation and sheath materials, converting fusible thermoplastic materials into non fusible elastomer materials. Cross linking radiation significantly improves the thermal, mechanical, and chemical properties of cable insulation materials.
The DC circuit is often affected by various unfavorable factors during operation, resulting in grounding, which prevents the system from operating normally. Grounding or becoming a grounding hazard can be caused by extrusion, poor cable manufacturing, unqualified insulation materials, low insulation performance, aging of DC system insulation, or the presence of certain damage defects. In addition, the invasion or biting of small animals in outdoor environments can also cause DC grounding faults. Therefore, in this case, armored and sheathed cables with rodent repellent function are generally used
