Study On Lightning Hazard And Protection Of Photovoltaic Power Generation System

As a clean and pollution-free renewable energy,photovoltaic power generation has been vigorously developed and utilized by all countries in the world.Increasing installed capacity and scale have also led to an increase in its footprint and the long exposure of many equipment to open areas,making it more vulnerable to lightning disasters and seriously affecting the safe and stable operation of the entire system.Therefore,it is necessary to conduct a detailed study on the lightning hazard of the photovoltaic power generation system and provide reference and guidance for the lightning protection of the photovoltaic power generation system.Firstly,the structure of the photovoltaic power generation system is introduced in this paper.The various ways of the damage caused by lightning to the photovoltaic power generation system and the concrete damage mechanism to the photovoltaic components are analyzed.And then the entire photovoltaic power generation system including the substation is divided into detailed lightning protection zones.Secondly,the generation and calculation of lightning induced overvoltage in two different lightning modes are analyzed in detail.The equivalent circuits of PV module were established to calculate induced circuit currents on the bypass diode.The results show that overvoltage in the loop increases with increasing of gradient of lightning current as well as distance between PV modules and lightning strike point.And the overvoltage induced by the corresponding loop in the natural lightning connection mode is greater than the independent lightning connection mode.When lightning strikes the frame of PV panels,the induced overvoltage amplitude of the 10/350?s waveform can still reach 8.1kV even if the circuit is within 2m from the frame,which greatly exceeds the circuit withstand voltage level.Magnitude and duration of induced current in bypass diode are smaller when bypass diodes are placed in reverse direction than in forward direction.Bypass diodes are vulnerable to lightning induced current and it is necessary to install surge protection devices such as transient voltage suppressor(TVS)and decrease the area of the loop.Then,a complete PV system model including PV array,combiner box,inverter,transmission cable is established by using ATP-EMTP software to simulate and analyze the lightning overvoltage of PV system.The results show that the lightning overvoltage and current waveforms of the device in the PV system show obvious characteristics of attenuation and oscillation,and the farther the device is from the lightning strike point,the lower the overvoltage and current amplitudes.With the increase of the lightning current amplitude,the overvoltage of the combiner box and the inverter shows an upward trend,and the overvoltage of the combiner box is affected more by the amplitude of the lightning current.The overvoltage under the impact of 30kA lightning current surpasses their overvoltage withstand capability of 8kV,which will cause great damage to the insulation of the device.The over-voltage amplitude of the device increases with the increase of the grounding resistance,and the probability of device damage increases accordingly.It is necessary to limit the grounding resistance of the grounding network to below 10? as much as possible.The installation of SPD can significantly reduce the overvoltage amplitude of the device.After the SPD is installed at the front of the inverter,the overvoltage is reduced by 71.6%,which is greatly suppressed and a good protection effect is achieved.Finally,the simulation study on the damage of the lightning invasion surge of photovoltaic power station is carried out by building the corresponding simulation model.The following conclusions can be obtained through the simulation results:when the lightning waves invade into PV substation whether through the grounding wire or the phase conductor,there will be a large surge overvoltage on the high voltage side of the transformer,which will pose a threat to the transformer.The lightning invasion wave overvoltage shows a trend of oscillation attenuation with time.The farther the lightning point is,the faster the attenuation is,and the amplitude of the overvoltage decreases with the increase of the distance of the lightning point.After the surge arrester is installed on the high voltage side of the transformer,the overvoltage is reduced by 75.5%when the lightning strikes the conductor at 100m from the transformer,which is lower than the withstand voltage value of 200kV on the high voltage side of the transformer,and the overvoltage waveform oscillation frequency also slows,indicating that the lightning arrester has obvious protective effect.However,its protective effect is greatly affected by the grounding resistance.When the grounding resistance increases from 2? to 80?,the overvoltage on the high voltage side of the transformer is increased by about 3 times.If the grounding resistance is too large,it will easily lead to the failure of the arrester protection.Therefore,the grounding resistance must be controlled within a relatively small range.