(1) Causes and hazards of lightning
Lightning is a common atmospheric discharge phenomenon. A large number of positive or negative charges are accumulated in different parts of the cloud layer. When the positive or negative charge in the cloud layer accumulates and reaches a certain strength, it will break down the air and open a narrow channel for forcible discharge. Because the energy released by lightning is quite large, the strong current, scorching high temperature, strong shock wave, drastic electrostatic field and strong electromagnetic radiation generated by lightning have brought a lot of harm to people. When lightning strikes a building directly, the strong current causes the building to be heated, vaporized and expanded, causing the building to burn or explode. When lightning strikes the air-termination device and the current is discharged to the ground along the down-conductor, it will cause fire or personal injury. Induction mine damage is also called secondary damage. Induction lightning is divided into two types: electrostatic induction lightning and electromagnetic induction lightning. Due to the large gradient of lightning current changes, a strong alternating magnetic field will be generated, causing the surrounding metal components to generate induced current. This current may discharge to surrounding objects. If there are combustibles nearby, it will cause fire and explosion, and when it is induced on the wires that are connected, it will cause strong damage to the equipment.
(2) Lightning protection and design requirements for solar photovoltaic power generation systems
①When choosing the construction site of a solar photovoltaic power generation system or a power station, try to avoid locations and places that are prone to lightning strikes.
② Try to avoid the projection of the lightning rod falling on the solar cell module.
③ According to the site conditions, different protective measures such as lightning rods, lightning protection strips and lightning protection nets can be used to protect against direct lightning and reduce the probability of lightning strikes. The shunting effect of multiple down-conductors can reduce the pressure drop of the down-conductor leads, reduce the risk of side impact, and reduce the magnetic field intensity generated by the down-conductor leakage.
④ In order to prevent lightning induction, all metal objects of the entire photovoltaic system, including the outer frame of the battery module, equipment, chassis cabinet shell, metal pipelines, etc., should be equipotentially connected to the joint grounding body, and can be grounded independently.
⑤ Install lightning protection devices step by step on the system circuit to implement multi-level protection, so that the lightning strike or switching surge current flows through the multi-level lightning protection devices. Generally, a DC power lightning arrester is used in the DC line part of the photovoltaic power generation system, and an AC lightning arrester is used in the AC line part after the inverter.