- General requirements
The overvoltage protection and grounding of the booster station area and the local inverter booster chamber of the photovoltaic power station should comply with the provisions of the current national standards GB/T50064 and GB/T50065, “Design Specification for overvoltage Protection and Insulation of AC Electrical Devices”.
Lightning protection of photovoltaic power station living auxiliary construction (structure) should comply with the provisions of the current national standard “Lightning Protection Design Code for Buildings” GB50057.
The grounding grid should be set up in the photovoltaic square array site. In addition to the artificial grounding pole, the grounding grid should also make full use of the metal components of the support foundation.
The grounding resistance of the PV square array should be less than 4 ohms.
Lightning protection requirements of photovoltaic power stations also need to refer to GB/T32512 and other national standards. The lightning protection of photovoltaic power stations should be planned in a unified way to be safe, reliable, technologically advanced and economically reasonable, so as to prevent and reduce the personal injury and equipment damage caused by lightning to photovoltaic power stations. Lightning protection design should be adapted to local conditions, considering the capacity of photovoltaic power station, regional annual thunderstorm intensity, soil geological conditions and investment costs and other factors, after technical and economic analysis and safety risk assessment, determine the corresponding lightning protection measures. The lightning protection system of the photovoltaic power station integrated with the building shall be integrated with the lightning protection system of the building.
- General requirements
2.1 Ground photovoltaic surge protection
The photovoltaic modules of the ground photovoltaic power station have fixed dip operation mode, tracking operation mode and concentrating operation mode, which are installed on the outdoor ground. In the photovoltaic field area, the overall height is less than 5m, but the area is large, except for the high-power concentrating module and the dual-axis tracking module.
According to “Technical Requirements for Lightning Protection of photovoltaic Power Stations” GB/T32512, lightning protection measures should be taken for the photovoltaic square array of photovoltaic power stations, other equipment of photovoltaic power generation units, booster stations in station areas, comprehensive buildings and other buildings. Lightning protection measures should not block photovoltaic modules. Photovoltaic module metal frame or clip should be well connected. According to the type of power station, the PV square should adopt the corresponding grounding network, and the working grounding and protection grounding should be planned in a unified manner. The common ground grid resistance should meet the requirement of the equipment for the minimum power frequency grounding resistance.
(1) Lightning protection for photovoltaic phalanx
Photovoltaic square array electrical lines should be protected against lightning electromagnetic pulse and lightning surge intrusion measures. The photovoltaic square metal components should be equipotential connected with the lightning protection device and grounded. The independent connector and discharge lead line should be kept at a sufficient safe distance from the ground photovoltaic square electrical device and line, which should meet the requirements of GB/T50065. An independent grounding device should be set for the independent connector outside the photovoltaic square array. Other lightning protection grounding devices should share the grounding network with the facilities in the station. The power frequency grounding resistance of the photovoltaic square grounding device in the ground photovoltaic power station should not be greater than 10 ohms, and the maximum value in the high-resistance area (resistivity greater than 2000 ohms ·m) should not be greater than 30 ohms. According to GB50797, the ground resistance must be less than 4 ohms.
The metal frame of the photovoltaic module is used as the connector, the metal bracket is used as the lead line and the grounding device is connected, which can prevent direct lightning strike. Because the highest point of the photovoltaic module of the ground photovoltaic power station is generally 2.5 ~ 5m away from the ground, except for the large concentrating photovoltaic module. The probability and frequency of lightning strike for photovoltaic modules in photovoltaic power stations are related to the height of equipment and buildings. According to the formula in GB50057, the probability and frequency of lightning strike for photovoltaic modules in ground photovoltaic power stations are very low.
According to the law of lightning strike, all conductive particles in the air, the ground has towering objects, the resistivity of the soil is small areas prone to lightning strike. Lightning current always selects the most conductive path, and the top of the towering, edge and corner electric field intensity is the largest, nearby gas ions, the most easy to produce lightning phenomenon. Therefore, the edges and corners of the metal frame of the PV module in the wide PV power plant site are most likely to be struck by lightning first.
(2) Lightning protection for photovoltaic equipment
Equipment such as bus box, inverter and local boost transformer should be connected and grounded at equal potential. Shielding measures should be taken for metal signal lines of other equipment of photovoltaic power generation unit. In the photovoltaic array of the bus box, inverter DC input side between the positive pole and the protection ground, between the negative pole and the protection ground, between the positive pole and the negative pole should be installed direct surge protector, AC surge protector should be installed in the AC output end of the inverter.
(3) Lightning protection in station area
The lightning protection and equipotential connection, grounding network structure, and grounding requirements of the switch station or booster station shall meet the requirements of GB/T50065.
Lightning rods or lightning wires can be used for direct lightning overvoltage protection in power plants and substations. For specific installation facilities, refer to GB/T50064.
According to the standard GB/T50064, the direct lightning overvoltage protection of the main workshop, main control room, substation control room and distribution device room of the power plant shall meet the following requirements:
1) main workshop of power plant, the main control room and power distribution equipment room don’t furnish direct lightning protection device, to protect the lightning rod of other equipment and installations, should not be installed in the independence of the main control room and substation on the roof of 35 kv and below, the steel structure and reinforced concrete structure has shielding effect of the structure of the workshop transformer substation can furnish direct lightning protection device.
2) The main workshop, main control room, substation control room and distribution device room in strong minefield should be protected by direct lightning strike.
3) When the main workshop is equipped with direct lightning avoidance protection device or lightning rod is installed on the main workshop for the protection of other equipment, it should be taken to strengthen the shunt, the ground point of the equipment is far away from the ground point of the lightning rod, and the ground point of the lightning rod is far away from the electrical equipment to prevent counter measures. A group of MOA (zinc oxide arrester) for rotating motors should be installed at the generator outlet near the lightning rod.
4) When direct lightning protection devices are installed on the roof of the main control room, the distribution device room and the substation under 35kV, the metal part of the roof should be grounded; Reinforced concrete structure roof, it should be welded into a net grounding; The roof of a non-conductive structure should be protected by a lightning protection belt. The grid of the lightning protection belt should be 8 to 10m. The grounding lead should be connected to the main grounding network every 10 to 20m, and a centralized grounding device should be installed at the connection point.
5) Power plants and substations in the canyon area should be protected by lightning lines.
6) Buildings or equipment already within the protection range of adjacent buildings may not be equipped with direct strike mine protection devices.
7) The metal shell of the equipment on the roof, the metal skin of the cable and the metal components of the building should be connected to the ground.
The lightning rod installed in the photovoltaic power station is mainly considered to protect the equipment in the booster station or switch station, and the lightning rod is generally not considered to be set up in the photovoltaic field area. Because even if the height of the lightning rod is increased again, but after the height exceeds 30m, the protection range of the lightning rod is not proportional to the height of the lightning rod. When the height of the lightning rod is greater than or equal to 120m, the lightning protection range is independent of the height of the lightning rod. It is also unrealistic and uneconomical to install multiple 30-120m independent lightning rods in the photovoltaic power station site, which will cause occlusion to the photovoltaic components in the photovoltaic area of the photovoltaic power station. Therefore, it is recommended to install lightning rods only in the station area.
Ground photovoltaic lightning protection
2.2Roof photovoltaic Lightning Protection
According to the “building lightning protection design code” GB50057, generally will choose the third type of lightning protection building roof implementation of photovoltaic development. The third type of lightning protection for external lightning protection of a building is the flash net, flash belt, or flash rod installed on the building, or the combination of flash net, flash belt, or flash rod can be used. Flash mesh and flash belt should be laid along the corners of the roof, ridge, eaves and eaves, which are vulnerable to lightning, and the grid should be composed of no more than 20m×20m or 24m×16m in the whole roof. When the height of the building exceeds 60m, the flash belt should be laid along the periphery of the roof first, and the flash belt should be located on the surface of the external wall or the vertical surface of the edge of the eaves, or on the surface of the external wall or the vertical plane of the edge of the eaves. In addition, the receivers should be connected to each other.
According to the “Lightning protection Design Code for buildings” GB50057, the special lead line should not be less than 2, and should be arranged evenly and symmetrically around the building and the inner courtyard, the spacing along the perimeter calculation should not be greater than 25m. When the span of the building is too large to set a lead line in the middle of the span, the lead line should be set at both ends of the span and the spacing of other leads should be reduced. The average spacing of the special lead line should not be more than 25m. The grounding of the lightning protection device should share the grounding device with the grounding of electrical and electronic systems, and should be connected to the metal pipeline at equal potential. The special grounding device of the external lightning protection device should be laid around the building as a ring grounding body. Buildings should use reinforced concrete roof, beam, column, the reinforcement in the foundation as a lead down and grounding device, when the parapet inside the roof steel mesh above the waterproof and concrete layer allowed not to protect, it is appropriate to use the roof steel mesh as a flashing device.
The photovoltaic module of the roof photovoltaic power station is installed on the roof of the building or the wall of the sunrise without shadow. In addition to making full use of the original lightning protection system of the building, it can also combine the characteristics of the roof photovoltaic module and take similar measures to prevent the direct lightning of the ground photovoltaic power station. Operation mode and tracking mode operation mode will be fixed Angle of photovoltaic modules ShanQi metal frame for lightning prevention, with metal stents for lightning protection downlead photovoltaic components, and installation of photovoltaic modules channel steel bracket welding or i-steel basis, each foundation beam welding points not less than two points, and the roof of the building lightning protection lightning protection facilities, such as (network) Using THE ORIGINAL LIGHTNING protection grounding, AND according to the lightning protection category of the building, according to the requirements of the code, add the equalized pressure belt on the foundation steel beam, to realize the prevention of direct lightning strike.
The lightning protection of the photovoltaic curtain wall can meet the lightning protection requirements as long as the building material side lightning protection measures are taken. The concrete method is to use the main reinforcement in the frame column of the building as the lead line, and the main reinforcement in the ring beam of each layer is welded, and the installation of the metal frame of the photovoltaic glass curtain wall is welded, forming a Faraday cage. The photovoltaic curtain wall is “embedded” in the Faraday cage for direct hit protection. When the height of the building exceeds 45m, take measures to prevent side lightning strikes. Make equal potential protection connections of pressure sharing rings every 6m or 12m according to the height of the floor, and connect metal objects such as railings, doors and Windows on the outer wall of 45m or above to the lightning protection device.
According to “Technical Requirements for Lightning Protection of photovoltaic Power Station” GB/T32512, the roof photovoltaic power station should be designed according to the lightning protection level of the building where the photovoltaic square is located. The metal supports between the photovoltaic square components of the rooftop photovoltaic power station should be connected to each other to form a grid, and their edges should be connected with the roof connection flash belt nearby.
2.3 Surface PV surge Protection
Because water has a higher electrical conductivity than soil, it is easier to release lightning currents into the earth. Therefore, it is considered that the potential difference of electrical damage caused by lightning is relatively small for photovoltaic power generation system installed on water surface compared with ground setting.
However, this does not mean that the installation of photovoltaic power generation system on the water surface is necessarily beneficial to lightning protection. The actual situation will vary greatly with the project environment, wiring situation, lightning location and other factors, which need to be analyzed on a case-by-case basis.
According to the particularity of surface photovoltaic, attention should be paid to the lightning surface counterattack problem, and also to the lightning discharge problem on the water surface.
The overvoltage protection and grounding of the booster station area and the local inverter booster chamber of the surface photovoltaic power station should comply with the current national standards
The requirements of GB/T50064 and GB/T50065 Design Specifications for overvoltage Protection and Insulation of AC Electrical Devices. Lightning protection of photovoltaic power station living auxiliary construction (structure) should comply with the provisions of the current national standard “Lightning Protection Design Code for Buildings” GB50057.
A horizontal grounding grid should be set in the photovoltaic square array site in the form of a ring grid, and the flow should be discharged through multiple ground points.
Ensure that the ground resistance is less than 4 ohms. In addition, according to the local probability of lightning directly hitting the water surface, the surge parameter requirements of the equipment should be improved accordingly.
Although the photovoltaic power station occupies a large area, the layout space is limited. In order to meet the requirements of grounding resistance, the design scheme of common grounding system for all stations is often adopted. Photovoltaic power station has its inherent characteristics compared with the grounding of thermal power plant and substation. The grounding system of the ground and surface photovoltaic power station can be self-contained, but the grounding system of the roof photovoltaic power station cannot be completely self-contained, and must be coordinated with the grounding system of the building carrier. When designing grounding, consider the requirements for lightning protection and grounding.
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