Because the most of the distributed rooftop PV system are installed in the open air with alarge distribution area, there is a hazard from direct and indirect lightning strikes. In orderto avoid lightning damage to the distributed rooftop PV system, it requires the proper lightning protection and earthing.
As fllowing, we’ll introduce the key points of lightning protection and design requirements of distributed rooftop PV system.
When choosing the location of distributed rooftop PV system, try to avoid the places where are prone to lightning strikes.
●External Lightning Protection
According to the PV system installation site conditions, different protective measures could be adopted to protect against direct lightning strikes to reduce the probability of lightning strikes, such as lightning rods, lightning protection belts and lightning protection
nets. And try to use multiple bonding conductors evenly arranged to introduce the lightning current into the ground, the shunting efect of multiple conductor system reduces the lead voltage drop, reduces the risk of side strikes, and reduces the intensity of the magnetic field generated by the leakage of the bonding conductor system.
In order to prevent lightning induction, all metal objects of the entire PV system shall be connected to the joint earthing equipotential body, including the outer frame equipment of the battery, the endlosure of metal cabinet, and the metal line pipe etc. And each part shall be grounded independently also.
●Surge Protection Devices (SPD)
Install the lightning protection devices step by step on the system loop to implement multi-level protections, so that lightning strikes or switching surge currents can leak through the muti-level lightning protection devices. Generll, DC power surge arresters are used on
the DC side of the PV system, and AC power surge arresters are used on the AC side behind the inverter. Next, well focus on explaining and analyzing SPD selection and earthing measures for the PV system.
Selection and Installation of SPD
According to the IEC61643 standard, the selection and installation of SPD are determined according to the actual situation on site, and it has very detailed description of the requirements. Figure 1 is the earthing system diagram of the distributed rooftop PV system,it would be easier for us to better understand the whole system construction and lightning protection measures.
The design of lightning protection for the distributed rooftop PV system is mainly divided into the following three different cases:
1.The roftop without direct lightning protection.
2.The rooftop has direct lightning protections and with the safe isolation distance.
3.The rooftop has direct lightning protection but does not have a safe isolation distance.For above different cases, position①②③④SPD selection should be carried out based on the fllowing conditions:
1.Distance between power distribution cabinet and inverter.
2.Distance between PV array and inverter.
3.The safe isolation distance “S” between lightning protection devices and the bonding conductor system and related equipment in the PV system (including photovoltaic panels, inverters, cables, and power distribution equipment).
Please refer to IEC 61643-31/32 for the calculation and judgement of SPD device selection.
Earthing and protective conductors should comply with IEC 60364-7-712:
1.Connecting conductors of SPDs for DC SPD connections to the main earthing terminal the conductors shall have a minimum cross section of 6 mm2 copper or equivalent for Class I tested SPDs and 16 mm2 copper or equivalent for Class I tested SPDs.
2.Functional earthing: for mechanical protection, the minimum cross-sectional area fora functional earthing conductor is 4 mm2 copper or equivalent.
3.Separate earth electrode: if a separate earth electrode is provided for the PV array, this electrode shall be connected to the main earthing terminal of the electrical insallation by main equipotential bonding conductors.
4.Bonding of PV metal structures: the bonding conductors (insulated or bare) shall have a minimum cross section of 4 mm2 copper or equivalent PV array bonding conductors shall be run as close to the positive and negative PV aray and or sub-array conductors as possible to reduce induced voltages due to lightning.
The lightning protection and earthing of distributed rooftop PV system is critical for the safe operation of PV power plant, need us to pay more attentions. Above we just explain the main considerations of the lightning protection design of a PV system, for more specific design rule and SPD device selection, you sill need to consult the regional professional insallers, and it’s requested to comply with local regulation requirements besides above IEC standards we have mentioned.
Growatt always put safety frst for the product design and PV plant system. Growatt provide full range of PV inverters which have been equipped with a built-in lightning protection module to protect the PV system safety. Take the new launched MAX 100-125KTL3-X LV flagship C&I inverter as an example, this model integrates Type I SPD protection devices for both DC and AC side. Below figure 3 has showed the dedicated SPD board of MAX 100-125KTL3-X LV model, it is a modular and separated board which is convenient for disassembly and replacement, easy for maintenance. The integrated SPD function of PV inverter could bring the cost saving and reduce the insallation difculties of the PV system.
Besides the SPD protection, MAX 100-125KTL3-X LV also integrates the PID and AFCI functions to protect your PV plant flly. It also creats many “highest” in the market. the highest power density and the highest power rating of a single unit C&I inverter, also has the highest string current up to 16A, perfectly compatible with 600W+ high power modules.