Surge Protection for Low Voltage Systems
Low-voltage equipment is designed for handling low voltages at consumer-level. This includes computing and telecommunications systems, power distribution grids and PV systems, and EV charging facilities. Exposure to sudden high voltage surges, for example, from switching or lightning, can damage or destroy low-voltage equipment. Protection of low-voltage equipment and systems from such phenomena is thus vital for human safety as well as preventing damages, and so understanding the processes and protective countermeasures is of great importance. This book offers a systematic and thorough treatise of the topic for researchers in industry and universities as well as utility experts and advanced students and more generally for all people involved in electromagnetic compatibility or designing surge protection systems and lightning protection systems. The book aims to provide answers to all readers' questions from the simplest to the most complicated, including guidance on the application of surge protective devices (SPD) illustrated by many cases studies. Following an introduction, chapters cover lightning and surges, risk assessment, standard environment, surge protection (surge protective components and surge protective devices), and their applications, new trends and unsolved challenges.
Inspec keywords: lightning protection; IEC standards; arresters; overvoltage protection; surge protection
Other keywords: poles and towers; power overhead lines; silicon compounds; arresters; lightning protection; surge protection; overvoltage protection; air gaps; resistors; IEC standards
Subjects: Education and training; General electrical engineering topics; Overhead power lines; Power system protection; Protection apparatus; Resistors; Power line supports, insulators and connectors
- Book DOI: 10.1049/PBPO182E
- Chapter DOI: 10.1049/PBPO182E
- ISBN: 9781839532658
- e-ISBN: 9781839532665
- Page count: 492
- Format: PDF
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Front Matter
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1 Introduction
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This paper is about the link between protection against lightning and surge protection dates back to the use of electricity in the United States. Shortly after the installation of overhead lines as a part of the US telegraph system infrastructure, damages of atmospheric origin began to appear. A paper written in 1847 by Joseph Henry (for whom the SI unit of inductance is named), then a professor at what is now Princeton University, provided a description of a simple air-gap device for use in reducing damages to telegraph lines from the results of such atmospheric discharges. Henry's proposed design recommended the installation of a wire connected to the earth at the bottom of a telegraph pole that would be attached to the pole up to a point within 0.5 inches (13 mm) of the telegraph line. Within the next few decades, the development of the technology became more sophisticated. With the advent of the light bulb, overhead power lines provided additional challenges. Nonlinear resistors, oxide film arrestors, the introduction of silicon carbide devices with nonactive and then active gaps to zinc-oxide devices ensued. With the development of sophisticated electronic systems and today's smart homes and offices, surge-protective devices (SPDs) for low-voltage applications require even greater sophistication and even smart SPDs.
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2 Lightning and surges
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In this chapter, focus is on lightning strikes to ground, i.e., the electrical discharges between the thunder cloud and the ground. Special attention to ground structures, such as buildings and electrical networks will be considered. Lightning strikes can affect electrical circuits in two ways: by direct strikes and by induced effects due to the electromagnetic fields generated by the high magnitude fast lightning current. Following lightning strikes, high current and high-voltage surges travel on electrical networks on both low-voltage (LV) and high-voltage systems. If and when these travelling surges reach sensitive electrical and/or electronic equipment, significant damage can occur if no adequate lightning protection or shielding is put in place. For completeness, switching surges on networks will be reviewed and their impact on the network will be addressed.
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3 Risk assessment
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The possible types of damages caused by lightning and surges (overvoltages or impulse current) to a structure and its connected lines should be evaluated as well as their frequency of occurrence and the extent of the associated damages. The method to perform this evaluation is a lightning risk assessment (LRA) as defined in IEC Standard 62305-2. This analysis aims to determine what are the most efficient protection means for the studied structure (lightning rods, mesh system, surge-protective devices (SPDs), Thunderstorm Warning System (TWS), etc.), where to locate the selected protection components and with which efficiency (level of protection).
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4 Standard environment
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Standards are often late compared to the market needs and manufacturers development of new products to meet those needs. It is typical that 3-5 years are needed to develop and publish a standard. The result is that technology will generally lead standards in terms of what is available in the marketplace. On the other hand, standards are a good indication of accepted norms for the technology that are currently established. Surge-protective devices (SPDs) are used in a number of increasing applications as new technologies are developed. An example was the rapid expansion of photovoltaic (PV) applications that led to an urgent demand for SPDs tailored to the application. It was urgent that standards be developed to address safety and performance tests for SPDs designed to be installed in the PV installations. This led to the development of product and application standards now published as IEC 61643-31 and IEC 61643-32, respectively. In the same way, the growing need for SPDs connected to DC power circuits and equipment for protection against indirect and direct effects of lightning or other transient over-voltages justified the current development of IEC 61643-41. There are many International Electrotechnical Commission (IEC) standards that incorporate the use of SPDs into their standards.
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5 Surge-protective components
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This chapter is about components that are commonly used to achieve surge protection. They can be either used in devices that are specially designed for this purpose or used in equipment's or systems that are dedicated to various applications other than specifically surge protection. They can be used alone or combined. They are commonly called SPC standing for surge-protection component.
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6 Surge protective devices
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A surge-protective device (SPD) is defined as a device containing at least one nonlinear component intended to limit surge voltages (transients) and to divert surge currents. This implicates that such a device is designed using one or more components that either show a continuous voltage-dependent decrease in impedance, or a sudden voltage-dependent change in impedance. An ideal SPD should under normal supply voltage and system conditions 'be invisible' and not influence the system characteristics in any way and as soon as a surge voltage appears limit the amplitude to a value low enough to avoid any damage to installations and equipment or malfunction of equipment, without any significant impact on power quality, e.g. avoiding any dips or even interruptions due to follow currents or slow recovery to a high-impedance state again.
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7 Application rules
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This paper is about the selection of surge-protective devices (SPDs) and their installation rules are generally not complex. For most of the cases, the path to follow is clear and straight forward. In a few circumstances, there are complexities either for selection of the appropriate SPDs (such as coping with superimposed high-frequency impulses, switching surges, high temporary overvoltages (TOVs)) or more generally during the installation process (lack of space in a panel board, need to install SPDs in another place instead of originally scheduled, difficulties to keep lead length short, etc.). There is then a need to accommodate these complexities by selecting other SPDs (such as with a better voltage protection level) or adding more SPDs to further reduce the overvoltages in front of equipment to be protected. Except in these cases, the rules are simple (it does not mean that the application of these rules is always simple). However, these rules are based on the assumption that protection is efficient. Even if true in a large majority of cases, the application of standard rules may not be sufficient in a few cases. Sometimes (see Sections 8.7 and 8.8), it is necessary to demonstrate protection efficiency. Then tests or calculations are needed and those make the selection process more complex.
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8 Specific application rules
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This section has sought to provide an overview of some of the more important aspects to be considered when installing SPDs on the US power distribution system, as well as providing some insight into the legal and legislative framework which govern such installations under the National Electric Code and ULs. In addition, it has briefly addressed some countries adopting similar voltages and frequency to North America, where SPDs designed for the US market are often installed.
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9 New trends
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Surge-protective device (SPD) is the core device to protect the equipment against over-voltage and surge current in the electrical and electronic systems. The safe and stable operation of SPD is very important for the lightning protection of the electrical and electronic systems. Therefore, the real-time monitoring of SPD working status is necessary to ensure the reliable operation of SPD. The safe operation of SPD cannot be fully guaranteed during the inspection period due to incorrect installation or the self-degradation failure during the period. With the rapid development of sensors and Internet of Things (IoT) in recent years, the periodical inspection of SPD is gradually upgraded to real-time online monitoring. It can not only monitor the surge information, the leakage current, the working temperature of SPD, the disconnection status of disconnectors and so on, but also to give warning or life prediction message when SPD comes to degradation or failure status through IoT. This new type SPD is usually called Smart SPD by the manufacturers and users.
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10 Ongoing issues and possible solutions
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Surge-protective device (SPD) protection characteristics depend on the surge protection components that are used inside and, in that direction, main evolutions are coming from a combination of components to achieve better protection characteristics rather than from breakthrough technologies. It is often expected that new surge protection components will approach better the ideal protection characteristics (impedance equals zero when there is a surge and open circuit for the remaining time) but basically, based, for example, on varistors, there are little improvement to notice at the present time. It is well known that it is possible to improve one characteristic of a varistor to meet a specific goal or to better suit an application, but it is generally associated with a degradation of another characteristic. Main progress in terms of varistors is presently coming from their shape that will better fit to the available space inside an SPD to maximize efficiency and minimize the size of SPDs. Size of SPDs is always a challenging issue and we will come back to this later when discussing installation rules. Regarding gaps, progress is mainly coming from their size that also decreases, from their surge withstand capability increase and the follow current (AC current that follows the flow of a surge when a gap operates) reduction.
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Back Matter
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