Renewable Energy

Lightning strikes and surge protection for solar power stations

2016/03/04

For complex systems such as solar power plants, it is necessary to assess the risk of damage from lightning strikes in accordance with IEC 62305-2 (EN 62305-2) and the results should be considered in the design. The goal of solar power plant protection is to protect the plant and PV array of the power station from fire (direct lightning strike) damage and protect the electrical and electronic systems (inverters, remote diagnostic systems, generator mains) from lightning electromagnetic pulses. The impact of (LEMP).

Flashing device and down conductor system

       In order to prevent direct lightning strikes on the photovoltaic array, it is necessary to arrange the solar modules within the protection range of the isolated lightning receptors. In accordance with the VdS Guiding Principles 2010, photovoltaic installations larger than 10 kW should be designed as “Class III” lightning protection systems. For the corresponding level of protection, the ball method is used to determine the height and number of lightning rods. In addition, in accordance with IEC 62305-3 (EN 62305-3), care should also be taken to maintain the separation distance between the photovoltaic support and the lightning rod. Similarly, the lightning protection of the operating room is also rated "Class III". The down conductor is connected to the grounding system through the ground busbar. Due to the risk of soil or cement corrosion at the ground busbar port, corrosion-resistant materials must be used or, if galvanized steel is used, take appropriate measures (eg sealing tape or heat shrink tubing) for protection.

Grounding system

       The grounding system of the photovoltaic equipment is designed as a ring grounding electrode (horizontal grounding electrode) with a network size of 20m×20m. The metal bracket of the fixed PV module is connected to the grounding system approximately every 10m. The grounding system of the plant uses a basic grounding pole in accordance with DIN 18014 (German standard). The grounding system of the photovoltaic installation and plant is connected to each other by conductors (V4A steel bars, 30mm x 3.5mm, or galvanized steel). Connecting the various grounding systems to each other can significantly reduce the total grounding resistance. An equipotential surface can be formed by a grounding system interconnected by a mutual mesh, which can significantly reduce the overvoltage generated by lightning on the connecting cable between the photovoltaic array and the building. The horizontal grounding poles are laid in at least 0.5M deep soil and are connected to each other in a grid shape using cross clamps. The joints in the soil must be wrapped with corrosion-resistant tape. This also applies to V4A steel bars laid in the soil.


Equipotential bonding

       In principle, all conductive parts entering the building from the outside must generally be connected to the equipotential bonding system. The requirement to complete these equipotential bonding requirements is that all uncharged metal parts are directly connected to the equipotential system, and live parts (such as cables) are indirectly connected to the equipotential bonding system by installing a surge protector. Equipotential bonding is preferably performed near the entrance to the building to prevent some lightning current from entering the building. In this case, the low-voltage power supply system in the plant can be protected with multi-pole composite lightning current and surge protectors.


       In addition, the input DC conductors of the PV inverters in the plant must be protected by a suitable spark gap-based lightning current protector, for example: a composite lightning current and a surge protector.

Lightning protection measures for photovoltaic arrays

       In order to reduce the mechanical stress generated in the solar module when the lightning receptor is struck, a surge protector with thermal monitoring function is installed in the generator junction box as close as possible to the photovoltaic generator. For voltages up to 1000V DC generator voltage, install a surge protector between the positive and negative poles to ground. Because the photovoltaic panel is within the protection range of the external lightning protection device, the SPD is sufficient to meet the protection requirements.

       In order to extend the time interval for periodic on-site inspection of the protection device, it has proven to be an effective method to use a surge protector with a floating contact to indicate the operating state of the thermal trip device.

       The surge protector in the generator junction box basically controls the regional protection of the photovoltaic device and ensures that interference associated with the wires and electromagnetic fields does not cause flashovers in the photovoltaic device.

 note

       Lightning protection for so-called "thin film photovoltaic modules" is beyond the scope of this consideration.

Lightning protection measures for information systems

       A remote diagnostic system is available in the plant for simple and fast functional inspection of photovoltaic installations. Interference with photovoltaic equipment can be detected and eliminated by operators early. The remote monitoring system continuously provides performance data for the photovoltaic device to optimize the output of the photovoltaic device. Wind speed, module temperature, and ambient temperature measurements are made by external sensors at the PV unit.

       These measurements can be read directly from the data acquisition unit. The data acquisition unit can also be connected to a computer PC and/or modem via an interface such as RS 232 or RS 485 so that the service engineer can determine the cause of the fault and eliminate the fault by remote diagnosis. The regulator modem is connected to the network terminal equipment (NTBA) of the ISDN access port. Like photovoltaic modules, wind speed and module temperature measurement sensors are also installed in the scope of lightning protection. In this way, no lightning current will occur in the measurement line, but transient overvoltages associated with the connecting wires may occur, which is the induction effect in the isolated lightning device during lightning strikes. In order to transmit the measurement data to the measuring unit reliably, without failure and continuously, it is necessary to install a surge protector in the cable of the sensor introduced into the building. When selecting a surge protector, you must ensure that the measured values are not affected. ISDN modems that forward measurement data via telecommunications networks are also required to be secure and reliable in order to continuously control and optimize the performance of the equipment. For this purpose, a surge protector is installed on the UKO interface of the ISDN modem upstream of the network terminal equipment. This surge protector also protects the network terminal equipment (NTBA) 230V power supply.


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