In recent years, the technological development of the photovoltaic industry has become faster and faster, the power of single modules has increased, and the current of strings has also increased. The current of high-power modules has reached more than 17A. In terms of system design, the use of high-power components and reasonable over-allocation can reduce the initial investment cost and cost of electricity of the system. The cost of AC and DC cables in the system is not low. How should the design and selection be made to reduce costs?
1. Selection of DC cables
DC cables are installed outdoors. It is generally recommended to select photovoltaic special cables that have been irradiated and cross-linked. After irradiation with high-energy electron beams, the molecular structure of the insulating layer material of the cable changes from linear to three-dimensional network molecular structure. The grade is increased from non-cross-linked 70°C to 90°C, 105°C, 125°C, 135°C, and even 150°C, which is 15-50% higher than the current carrying capacity of cables of the same specification, and can withstand severe temperature changes and chemical erosion. Used outdoors for over 25 years. When selecting DC cables, it is necessary to choose products from regular manufacturers with relevant certifications to ensure long-term outdoor use.
At present, PV DC cables are mostly used as 4 square cables of PV1-F 1*4, but with the increase of the current of photovoltaic modules and the increase of the power of single inverter, the length of DC cables is also increasing, and the length of 6 square cables DC cable applications are also increasing.
According to relevant regulations, it is generally recommended that the loss of photovoltaic DC should not exceed 2%. We use this standard to design how to choose DC cables. The line resistance of PV1-F 1*4mm2 DC cables is 4.6mΩ/meter, and the line resistance of PV 6mm2 DC cables It is 3.1mΩ/meter, assuming that the working voltage of the DC module is 600V, the 2% voltage drop loss is 12V, assuming the current of the module is 13A, using a 4mm2 DC cable, the distance between the farthest end of the module and the inverter is recommended not to exceed 120 meters ( Single string, without positive and negative poles), if the distance is greater than this, it is recommended to choose a 6mm2 DC cable, but it is recommended that the distance between the farthest end of the module and the inverter should not exceed 170 meters.
2. Selection of AC cables
In order to reduce the system cost, the components and inverters of photovoltaic power plants are rarely configured according to the ratio of 1:1, but a certain amount of over-allocation is designed according to the lighting conditions and project needs. For example, if a 110KW module is selected, a 100KW inverter is selected, and the maximum AC output current is about 158A based on the 1.1 times over-provision calculation on the AC side of the inverter. The AC cable can be selected according to the maximum output current of the inverter. Because no matter how much the components are over-provisioned, the AC input current of the inverter will never exceed the maximum output current of the inverter.
Commonly used AC copper cables for photovoltaic systems include BVR and YJV and other types. BVR means copper core PVC insulated flexible wires, and YJV XLPE insulated power cables. When selecting types, pay attention to the voltage level and temperature level of the cables. , to choose a flame-retardant type, the cable specification is expressed by the number of cores, the nominal cross-section and the voltage level: single-core branch cable specification representation, 1*nominal cross-section, such as: 1*25mm 0.6/1kV, which means a 25 square cable. Multi-core twisted branch cable specification representation, the number of cables in the same loop * nominal cross-section, such as: 3*50+2*25mm 0.6/1KV, which means three live wires of 50 square meters, one neutral wire of 25 square meters and A 25 square ground wire.
Post time: Dec-19-2022