In recent years, the application of solar energy (PV) power generation has become increasingly widespread and developed rapidly. In addition to the main equipment, such as PV modules, inverters and step-up transformers, the photovoltaic cable materials that are connected together also play a vital role in the overall profitability, operation safety and efficiency of the photovoltaic power station, The following is a detailed introduction to the use and use environment of common cables and materials in photovoltaic power stations.
Cables can be divided into DC cables and AC cables according to the system of photovoltaic power station, and are classified as follows according to the purpose and use environment:
1．DC cable
(1)Tandem cables between components.
(2)Parallel cables between strings and between strings and DC distribution box (combiner box).
(3)Cable from DC distribution box to inverter.
The above cables are DC cables, which are mostly laid outdoors. They need to be moisture-proof, sun-proof, cold-resistant, heat-resistant, and UV-resistant. In some special environments, they also need to be protected against acid and alkali and other chemicals.
2．AC cable
(1)Connecting cable from inverter to step-up transformer.
(2)Connecting cable from step-up transformer to power distribution device.
(3)Connecting cable from power distribution device to power grid or user.
This part of cable is AC load cable, which is laid in indoor environment, and can be selected according to the general power cable selection requirements.
3. PV special cable
A large number of DC cables in photovoltaic power stations need to be laid outdoors, and the environmental conditions are bad. The cable materials should be determined according to the resistance to ultraviolet radiation, ozone, severe temperature changes and chemical erosion. Long-term use of cables made of ordinary materials in this environment will cause the cable sheath to be fragile and even decompose the cable insulation layer. These conditions will directly damage the cable system, and also increase the risk of cable short circuit. In the medium and long term, the possibility of fire or personal injury is also higher, greatly affecting the service life of the system.
Therefore, it is very necessary to use photovoltaic special cables and components in photovoltaic power stations. With the continuous development of the photovoltaic industry, the market of photovoltaic supporting parts has gradually formed. As for cables, a variety 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 weather and mechanical impact. For example, RADOX cable is a special solar cable developed according to the international standard IEC216. In outdoor environment, its service life is 8 times that of rubber cable and 32 times that of PVC cable. PV special cables and components not only have good weather resistance, UV resistance and ozone resistance, but also can withstand a wider range of temperature changes (for example, from - 40 to 125 ℃). In Europe, technicians have tested that the temperature value measured on the roof is as high as 100~110 ℃.
4.Cable conductor material
The DC cables used in photovoltaic power stations are mostly used for outdoor long-term work. Due to the limitation of construction conditions, connectors are mostly used for cable connection. Cable conductor materials can be divided into copper core and aluminum core. Copper core cable has the characteristics of better oxidation resistance, long service life, better stability, low voltage drop and low power loss than aluminum; In construction, because the copper core is flexible and the allowable bending radius is small, it is easy to turn and pipe; Moreover, the copper core is anti-fatigue and not easy to break after repeated bending, so the wiring is convenient; At the same time, the copper core has high mechanical strength and can withstand large mechanical tension, which brings great convenience to construction and laying, and also creates conditions for mechanized construction. On the contrary, aluminum-core cables are prone to oxidation (electrochemical reaction) due to the chemical characteristics of aluminum materials, especially creep, which may lead to failure.
Therefore, copper cables have prominent advantages in the use of photovoltaic power stations, especially in the field of directly buried cable power supply. It can reduce the accident rate, improve the reliability of power supply, and facilitate construction, operation and maintenance. This is the reason why copper cables are mainly used in underground cable power supply in China.
5. Cable insulating sheath material
During the installation, operation and maintenance of the photovoltaic power station, the cable may be laid in the soil below the ground, in the weeds and riprap, on the sharp edge of the roof structure, and exposed in the air, and the cable may withstand the impact of various external forces. If the strength of the cable sheath is not enough, the cable insulation will be damaged, which will affect the service life of the entire cable, or lead to short circuit, fire and personal injury hazards. The cable scientific research and technical personnel found that the materials that have been cross-linked by radiation have higher mechanical strength than those before radiation treatment. Cross-linking process has changed the chemical structure of the polymer of the cable insulation and sheath material, and the fusible thermoplastic material has been converted to the non-fusible elastomer material. Cross-linking radiation has significantly improved the thermal, mechanical and chemical properties of the cable insulation material.
The DC circuit is often affected by a variety of adverse factors during operation, resulting in grounding, which makes the system unable to operate normally. Such as extrusion, poor cable manufacturing, unqualified insulation materials, low insulation performance, aging of DC system insulation, or some damage defects can cause grounding or become a potential grounding hazard. In addition, the invasion or bite of small animals in outdoor environment will also cause DC grounding fault. Therefore, in this case, armored cables with rat-proof sheath are generally used.
