Summary
With the continuous development and utilization of renewable energy, photovoltaic power plants based on the use of solar energy began to appear in large numbers. Photovoltaic power plants are the medium that converts light energy into electrical energy. Therefore, it is of great significance to strengthen the research on the design of photovoltaic power plant electrical systems to ensure the normal operation of the power system. In this article, the author discusses the main points of the electrical system design of the ground-connected photovoltaic power station from the three aspects of the main wiring, lightning protection and cable laying, hoping to provide a certain reference for the development of the photovoltaic industry.
At present, the ground grid-connected photovoltaic power station has a rapid development speed. In this article, the author discusses the design points of the electrical system in the photovoltaic power station and its role in the safety of the photovoltaic power station.
I. Analysis of the main wiring design of photovoltaic power plants
When designing the main wiring of a photovoltaic power plant, many factors such as the installed capacity of the power station, the main mode of access to the system, and the main characteristics of the station layout and electrical equipment should be fully considered. The main wiring should follow the principle of "reliable power, flexible operation, saving money, and convenient operation." If the PV power station to 35kV or higher level of boost, this time, the internal wiring of photovoltaic power plants mainly in the case of Level 1 or Level 2 booster, and therefore, should be analyzed from the main terminal in the form of technical and economic aspects.
The power system of the photovoltaic station's light station mainly uses the 0.38kV class, and the grounding system used is the neutral point shared by the lighting and power network. As long as the proper technology is used, it is possible to introduce power from the external network. The connection of the backup power is mainly completed by the power generation bus of the photovoltaic power station, and an automatic power input device for the equipment should be added between the two power supplies. If the scale of the photovoltaic power plant is not very large, then the area of ​​the occupied land will be much smaller. In the area of ​​inverter area, the load is used for electricity, and the low-voltage power distribution device is used for the connection; if the scale of the photovoltaic power plant is large, the occupied area is also large. At this time, the cable voltage drop is relatively large, and the cable is selected at the same time. The cross-section is also relatively large. At this time, the power supply in the inverter zone should be connected from the low-voltage side to the low-voltage side. At the same time, the two adjacent box changes can be used as backup devices.
II. Analysis of Lightning Protection Design for Photovoltaic Power Plants
(I) Lightning Protection of Photovoltaic Power Plants
Lightning protection projects have a very important role in photovoltaic power plants. Therefore, when the PV power station lightning protection design should be in accordance with relevant provisions, while respecting the main principles of "overall defense in a comprehensive, multi-layered protection, defense in depth" to prevent lightning damage to the power plant to the maximum extent. Because lightning strikes are destroyed in three ways: direct lightning, induced lightning, and lightning counterattack. Therefore, when designing for lightning protection, the characteristics of each building and different types of lightning strikes must be fully considered.
1, protection against direct lightning strikes
In the grid-connected photovoltaic power generation project, photovoltaic equipment is used in many ways and the range of deployment is relatively large. If a single lightning protection device is constructed, its role is very limited. At the same time, if excessive lightning protection equipment is installed, It will also increase the investment cost of the project. Therefore, the most effective lightning protection method is to connect the metal components of the photovoltaic power station with the ground in the station area. If a lightning strike occurs, the grounding line connected with the metal components will lead the mine to the ground. For a photovoltaic power station, lightning protection can be achieved by installing a lightning protection strip on the roof. When the lightning protection device is in contact with the thunderbolt, the downlead will immediately have a high potential, which will cause a sharp rise in the low potential around the lightning protection system, causing certain damage to the power station staff and equipment. Therefore, in order to prevent this phenomenon from occurring, the most concise thing is to use a pressure equalizing ring to connect the high potential with the low potential.
2. Protection against induced lightning strikes
Inductive lightning strikes are mainly caused by electrostatic induction, and electromagnetic induction can also produce induced lightning strikes. Induced lightning strikes increase the voltage and damage the electronic equipment inside the building. In photovoltaic power generation systems, to prevent induced lightning strikes, the main task should be to ensure that inductive lightnings do not enter the room through the outside world, thus affecting indoor equipment. Lightning invasion of photovoltaic systems mainly through two basic approaches, the first is through the AC grid and intruded into the power supply system, and secondly through the photovoltaic system components matrix DC invasive photovoltaic power generation system. At this time, lightning protection devices should be installed next to the DC and DC converters inside the PV system and the internal AC and DC inverters to ensure the safety of the line. In addition, lightning protection should be installed at every box change and outlet of the switch cabinet so as to prevent the induced lightning from damaging these places.
3, protection against lightning strike
When protecting against lightning strikes, equipotential measures should be taken. The so-called equipotential processing can also be treated as a common ground. In other words, the work site, the lightning protection zone, and the protection zone must be connected by means of equipotential bonding so that the potential of each point is equal.
(II) Grounding research of photovoltaic system
The commonly used grounding method for photovoltaic systems is grounding with horizontal grounding and supplemented by vertical grounding. In addition, it also includes square-hole composite grounding networks with closed edges. When designing the grounding method, it must be done according to the actual situation. Under normal circumstances, vertical grounding should be carried out using galvanized steel pipes, and they must be welded to horizontally laid flat steels. The lightning protection zone of the building roof and the grounding of the main power grid should also be provided with vertical ground poles, so as to ensure timely lightning diversion when the lightning strikes the potential. In addition, the beam and column reinforcement of the building should be connected together, so that the natural grounding body and the main ground network are connected to each other, so that the impact of lightning on the building can be avoided. In addition, anti-corrosion measures for grounding devices must be made. The material of the grounding device may be a hot-dip galvanized material or a copper material, both of which have anti-corrosion properties.
III. Analysis of the laying of photovoltaic power plant cables
Large and medium-sized photovoltaic power plants are bulky and occupy a relatively large area. If a radiation connection is used, connecting the power generation module of each unit in the power station to the photovoltaic power generation bus will not affect the entire power plant even if the power generation module fails. However, the number of cables and the number of switchgears have increased significantly. In order to reduce the number of cables laid, the original radiating connection can be changed to a "T" type connection. In addition, in some mountainous areas, it is necessary to use an integrated laying method to lay cables. For example, for a 30 MW ground photovoltaic power station, the site of this power station is not flat and has some fluctuations. If you use a full-range cable, not only is the construction more difficult, but the cost is also higher. After conducting a careful survey of the topography of a photovoltaic power station, the use of overhead lines plus direct burial methods was clarified. When laying the cable, it is necessary to scientifically plan the path of the circuit so as to make the line as short as possible, thereby saving the cable. After the design, the 35kV cable only needs 1.6 kilometers, and the overhead line is 5 kilometers, which can save a lot of money.
For the photovoltaic power station on the flat ground, the cable laying method is generally carried out by means of direct burial. The buried cable should be laid under the frozen soil. At present, most of the photovoltaic power plants are located in the northwest of China, where the frozen ground is relatively deep, and if the cables are buried directly underground, it will consume a very large amount of work. Therefore, use cold-resistant cables at this time. When laying cold-resistant cables, set aside a certain amount. In addition, in order to ensure that the cable will not be frozen, a protective tube should be attached to the cable. As a result, not only can save a large part of funds, but also to ensure the normal operation of the cable. For mountain photovoltaic power stations, the laying of cables is best carried out using a cable bridge and direct burial. Cable bridges should be laid along the topography of the terrain. At the same time, the effects of loose water and weeds on the laying of cables should also be fully considered. The height of the cable bridge must be more than 40 cm. For the cable tray material, it is best to use a galvanized tray or a fiberglass tray.
Conclusion
To sum up, with the continuous development and utilization of renewable energy, photovoltaic power plants based on the use of solar energy began to appear in large numbers. Photovoltaic power plants are the medium that converts light energy into electrical energy. Therefore, it is of great significance to strengthen research on the design of photovoltaic power plant electrical systems to ensure the normal operation of the power system. In this article, the author discusses the main points of the electrical system design of the ground-connected photovoltaic power station from the three aspects of the main wiring, lightning protection and cable laying, hoping to provide a certain reference for the development of the photovoltaic industry.
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