| Author: | Zhang, Yang |
| Title: | Lightning protection for large-scale photovoltaic systems |
| Advisors: | Du, Ya-ping (BSE) |
| Degree: | Ph.D. |
| Year: | 2021 |
| Subject: | Photovoltaic power systems Lightning protection Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Building Services Engineering |
| Pages: | 187 pages : color illustrations |
| Language: | English |
| Abstract: | As clean and renewable energy, the photovoltaic (PV) technique has been developing vigorously in recent decades and is utilized by countries all over the world. With the increasing installed capacity of the PV system, the safety issues of PV systems draw a lot of attention from both the academy and industry. Since the PV equipment is exposed in open areas, lightning becomes the main cause of PV failure. It is necessary to investigate the damage mechanism of lightning hazards in PV systems and provide guidance for the lightning protection of the system. Studies related to PV system lightning protection is insufficient. From the view of modelling, the lightning transient model for PV cells is not fully developed. Various PV models have been adopted to study the lightning transient in the PV systems. However, all these models adopt a certain level of simplification in the simulation due to the hardness of modelling complex wiring in PV systems. They cannot provide a complete and systematic evaluation of the lightning transient in PV systems. Therefore, an efficient modelling method for the PV systems is necessary for effective lightning protection design. From the view of investigation and engineering applications, the lightning protection research of PV systems mainly focuses on surge protection devices (SPDs) selection and PV ground grid design. However, the work concerning SPDs selection has limited reference value due to using over-simplified models for evaluation. Most of the researches on PV ground grid design just focus on a ground grid system that buried under the ground, without fully considering the connection of other PV system structure that installed in the air. Moreover, there is no work to evaluate the waveform and amplitude of the overvoltage that the PV panels and bypass diodes will suffer in the PV system during lightning strikes. Another drawback of previous studies is that they only focus on discussion on the lightning transient behaviour in the system or presenting the experimental phenomenon. However, no solutions or improvements for the lightning protection design are proposed. Thus, their contribution to practical engineering is limited. From the view of standards and practical codes, the current standard did not consider the specific configuration of the PV system. Most of the standards for PV lightning protection adopt general lightning protection regulations based on that developed for buildings or substations. Consequently, their reliability on the protection of PV systems is not fully validated. To solve these problems, this work presents a comprehensive study on lightning protection of PV systems from modelling to practical scenario analysis and design guidelines. The main contribution of the thesis is summarized as follows: (1) Systematic modelling of PV systems is proposed. The modelling of major components in the PV systems including the C-profile supporting structure, PV cable, wiring in the PV panel is presented in detail. The frequency-dependent effects and ferromagnetic properties of structural steel are taken into account. The PV cell model which exhibits non-linear characteristics under lightning current is also developed. (2) Failure modes of the PV system are discussed elaborately in the work. Factors that need to be considered while evaluating the lightning transient behaviour under each failure mode are demonstrated through theoretical analysis and simulation work. (3) Three types of lightning incidents, namely failure of PV inverters, breakdown of bypass diodes, and arcing between metallic parts are investigated. Both bypass diode breakdown and arcing-related incidents in the PV systems have not been analysed systemically in the literature. To go a step further, several protection measures against lightning to the PV systems are proposed to achieve more effective protection performance. (4) A comprehensive study is conducted to analyse the structure design of the PV system that will influence the induced voltage in the PV inverter. The influences of the mounting systems, lightning protection systems, PV frames, and DC cable arrangements are thoroughly investigated. The induced voltage between the positive and negative cable can be largely shielded by a select proper PV structure without using any additional SPDs. The results can guide PV system installations for maximizing lightning protection performance. (5) The grounding grid configurations of the PV system are investigated, and the transferred voltages between the DC cables and supporting structures at different points in the PV system are evaluated. A novel grounding grid arrangement that is simple to implement and cost-effective is proposed. Moreover, with the proposed arrangement, the soil with higher resistivity does not worsen the performance of lightning protection. On the contrary, the PV system will experience less residual voltage when the soil resistivity is high. This means the site selection of a PV plant will not be limited by the soil resistivity when lightning protection is an issue of concern. This work presents my efforts in both PV system modelling and scenario analysis. This work will benefit the PV modelling theory, provide solutions for the lightning protection design of PV systems, and also help the industry to develop the standard for PV system lightning. |
| Rights: | All rights reserved |
| Access: | open access |
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