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81-84 Lightning protection of photovoltaic power plant

Author: Source: Datetime: 2016-12-30 16:59:27
4.1.8 Lightning protection of photovoltaic power plant
Photovoltaic power station layout in the open flat desert Gobi or on the beach, due to the lack of tall buildings and trees, prone to lightning events, especially in lightning-prone areas. On the other hand, the lightning protection grounding of the PV power plant appears to be simple but critical. It is directly related to the operation of solar cell modules, photovoltaic array, AC / DC cables, inverters, transformers and the safety of power station maintenance personnel.

4.1.8.1 Current status
Solar photovoltaic power generation as an emerging environmentally friendly power generation technology and industry, there is no independent domestic design specifications to clear how the lightning protection of photovoltaic power plant grounding design. At present, most of the domestic based on "building lightning protection design specifications GB 50057 - 2010" and the power system design specifications related to lightning protection to carry out reference design, often targeted is not strong, lightning grounding effect and investment differences.
Japan is more common in the application of solar photovoltaic power generation, because of its geographical characteristics, can be used to arrange solar cells square large open space is not much, photovoltaic power generation construction scale are small, solar cells are usually with buildings, small farms And other unified and coordinated layout, covers an area of small, the protection against lightning directly to the use of lightning protection near the building to take into account the scope of protection.
Domestic Shanghai Chongming Island 1MW solar photovoltaic power generation project, part of the solar panel aluminum frame around the installation of the length of about 40mm lightning rod for each solar panels directly lightning protection, lightning rod is very short, but the layout of intensive, the number of more .
Shanghai Nanhui New Area, Lingang New City Heavy Equipment Industrial Zone, the top of the building solar photovoltaic projects, the choice of fixed discharge lightning rod to achieve direct lightning protection.

4.1.8.2 (Lightning Protection Design Code for Buildings GB 50057-2010 "Lightning Protection Project for the Lightning Protection Reference 1
Lightning as a natural phenomenon, with a strong uncertainty. According to the types of buildings, the importance of the degree of damage, and many other factors, the building lightning classification, to develop a "building lightning protection design specifications", clearly different levels of buildings to take different lightning protection measures. In accordance with what norms to define the large-scale solar photovoltaic power plant lightning protection level, there is no uniform standard in the country, in some literature will be solar photovoltaic power plant lightning protection level as three.
Solar panels produce direct current in the sunlight, the DC output of many solar modules is connected in series through the cable, after the parallel connection, along the cable tray, cable tray, etc. to the inverter, the inverter DC inverter into AC And boost to the grid. In the whole solar photovoltaic power generation system, the DC output part accounts for a large proportion, it can be said in a large area of the square of the solar cells, DC cables, cable trays, DC converters and other electrical equipment interspersed layout. If the PV power plant as a power system, in accordance with the relevant norms of the power system design, the core of concern will be the power system AC electrical equipment lightning protection grounding. PV power projects and power systems in the conventional power plant, power transmission system is different, even with the small power transmission project, its importance and degree of damage after the occurrence of the disaster is also different. Simply use the power system specifications for AC electrical equipment lightning protection grounding design, does not meet the characteristics of photovoltaic power generation project requirements.
As the square of solar cells and inverter booster height is usually not high 5m, a measure of height, in accordance with the "Building Lightning Protection Design Code" can not consider the direct lightning protection; However, the square area of solar cells, batteries Of the components used aluminum alloy frame, the panels are used angle, channel and other fixed, are good electrical properties of the metal material. In the large-scale open-air layout vulnerable to direct lightning damage, at the same time, thunderclouds easily in the solar cell internal circuit, solar cell module frame and its support structure to form induced over-voltage.
Therefore, considering the location of solar power projects in the location of the average number of thunderstorm days and the plate area, layout and other conditions, an objective analysis of the solar array phalanx suffer from the probability of lightning directly, and with reference to "building lightning protection design specifications" .

4.1.8.3 The necessity of the design of solar battery square lightning protection
Large-scale photovoltaic power plant solar array is a non-construction type of open space, the site open and open, subject to the probability of direct lightning strike than ordinary non-construction type open space to be large.
In accordance with China's "Building Lightning Protection Design Code," Section 3.5.5: "The large concentration of grain, cotton and flammable open-air yard, should be used to prevent lightning strokes directly when the number of lightning stroke is greater than or Equal to 0.06, it is appropriate to adopt an independent lightning rod or overhead lightning protection line direct lightning strikes.Independent lightning rod and overhead lightning protection line of the ball radius h desirable 100m ". This provision is mainly directed against lightning may cause flammable material fire accident.
Although large-scale solar array is not flammable, but a huge investment in photovoltaic power plants. At the same time, the cost of large-scale photovoltaic power generation is higher, the power loss caused by lightning is also larger. From the perspective of security, the square of the battery does not exist fire risk, but from the perspective of reducing economic losses, the solar cell square with reference to "Building Lightning Protection Design Code" for lightning protection design is very necessary.

4.1.8.4 Lightning protection grounding design
(1) Direct lightning protection

According to the statistics of many years, the monthly mean thunderstorm days of the sites where PV power stations are built are listed in Table 4-11.

Season Spring Summer Autumn Winter In total
Thunderstorm days Several days Several days Several days Several days Several days

That is, an area of average annual thunderstorm days for several days, belong to multiple minefield (or less minefields).
Taking into account the average annual thunderstorm days and the solar panel area and other factors, can be used to achieve lightning rod photovoltaic power plant within the square of the square lightning protection.
① ordinary lightning rod is a common type of lightning protection passive lightning, the installation of the general height of 20 ~ 40m, the need to set up an independent steel structure or ring pin tower. Ordinary lightning rods on the solar cell phalanx of the sun block serious, so the solar cell square should not use ordinary lightning rod.
② advance discharge lightning rod is a chain reaction device with active lightning protection system. It is based on the traditional lightning rod to increase the active trigger system, ahead of the ordinary lightning rod to produce the upstream head to attract lightning, thus increasing the scope of protection of lightning rod, compared to ordinary lightning rod to reduce installation height. The use of early discharge lightning rod, can greatly reduce the number of lightning rod, reducing the installation height of the lightning rod, reducing the block on the solar cell impact.
Early discharge lightning rod has been used in tens of thousands of projects around the world, such as Shanghai World Trade Center Square, Pudong Airport and many other high-rise buildings, power plants, refineries, airports, microwave stations and so on.
So the project design stage can be considered the use of early discharge lightning rod and proposed to meet the characteristics of photovoltaic power generation, hoping to tender through the equipment manufacturers to produce a reliable controllable type of advance and retractable discharge lightning rod. This lightning rod in the thunderstorm weather needle body for the solar cell square array lightning protection ready. In clear weather, the lightning rod body shrink up, will not form a shadow block solar panels.
According to the terrain of photovoltaic power station site ups and downs and the layout of the solar array square to determine the total number of sets required to set the height of 10m controllable type of advance and retractable discharge lightning rod. As the calculation formula for the lightning protection scope of the early discharge has no relevant standards and regulations in China, the calculation of the protection range of the lightning discharge can be carried out according to the French NFC17-102 standard.
(2) other areas of direct lightning protection
In the inverter boost room, partition high and low voltage power distribution room, diesel generator room, 10kV power distribution control room and building roofs and other buildings to set lightning protection for direct lightning protection.
AC side of the lightning protection in accordance with the power system industry standard "AC electrical installations over-voltage protection and insulation coordination" to carry out in the 110kV booster station set up a number of ordinary high-30m free-standing lightning rod to sell 110kV power distribution device, the main transformer , Outdoor SVC devices and other direct lightning protection. 110kV line set lightning line.
(3) induction lightning protection
Photovoltaic power plants can be grounded, shunt, shielding, are equal pressure and other methods to effectively protect the mine to protect the personal and equipment safety.
① ground PV power plant can be lightning protection grounding, protective grounding, grounding for the work of a common grounding device. The entire photovoltaic system to ensure personal safety, all electrical equipment shell should be connected to a dedicated grounding trunk, the whole station grounding grid design principles for the level of grounding, supplemented by vertical grounding of artificial composite grounding network. Ground resistance is not greater than 10Ω to consider; llOkV booster station grounding resistance allowable value of 0.5Ω.
Power station in the entire site layout has both decentralized, but also has a certain concentration. Therefore, for each of the relatively concentrated square array area, respectively, set up a common grounding system, the region and through the cable tray between the inverter AC output to the booster station 10kV distribution room, the actual area between the cable Bridge and the grounding network connection to form a large, unified common grounding system. Photovoltaic power plant site is different, different soil resistivity.
Grounding the solar array consists of two aspects: one is the connection of solar panels and mounting brackets, on the other hand is the connection between the bracket and the earth. Solar panel aluminum frame on the left for the installation of ground wire bolt hole location, the construction of a dedicated insulated grounding wire to the battery aluminum alloy frame and the battery plate bracket can be reliably connected. In the solar panels installed between the rigid support measures to form a whole horizontal grounding and according to the phalanx of the site where the soil resistivity, soil area, soil thickness, paint continuity and other factors, respectively, or the joint use of physical grounding Modules, copper-clad steel vertical grounding electrode, anti-corrosion and other different grounding materials grounding material, in the use of solar panels installed base of the excavation conditions, while setting meet the requirements of the vertical grounding.
② shunt To complete the lightning induction over-current shunt, DC converters at all levels in the box, inverter equipped with surge protector, in the 10kV bus, 110kV bus installed on the zinc oxide arrester, the main transformer neutral installed a Group zinc oxide arrester and parallel discharge gap.
③ shielding In the photovoltaic power station, solar panels are placed in the open air environment, the shield is mainly for the inverter boost room, high and low voltage distribution room, control room, electrical cables and other electrical equipment to reduce the basic measures to reduce the electromagnetic wave . Such as the inverter to boost the room, 10kV power distribution control room and other buildings within the beam-column reinforcement, roof lightning lead down line connected, and with the power plant's main grounding network is not less than two reliable connections to form a closed Good Faraday cage; and all electrical equipment, metal casing and Faraday cage well connected to complete the external shielding measures.
④ equipotential photovoltaic power plants within the principle of lightning according to zoning, in the same mine and sub-district to do the junction of equipotential bonding.
Of course, the design content of the large-scale centralized grid-connected PV power plant should also include the relevant civil engineering design, water supply and drainage and fire protection, environmental protection, labor safety and industrial hygiene design, and so on. See related literature.
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