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Adoption of IEC 62305 As the Basis for One Major U.S. Electric Utility's Lightning Protection Standard

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Adoption of IEC 62305 As the Basis for One Major U.S. Electric Utility's Lightning Protection Standard Adoption of IEC 62305 as the Basis for One Major U.S. Electric Utility’s Lightning Protection Standard Gary T. Brandon Duke Energy Charlotte, NC USA [email protected] Abstract— Lightning protection systems designed for electric In 1882, the Royal Meteorological Society convened a power generation facilities in the United States, by default, are lightning rod conference to formulate the existing knowledge typically designed according to the specifications of NFPA 780, as of atmospheric electricity for the protection of property from this is the governing lightning protection standard in this damage by lightning, as well as, to prepare and issue a general country. These facilities use the design guidance of this standard code of rules for the erection of lightning conductors in an even though this standard explicitly states that electric effort to take action for the public. The Report of the Lightning generating facilities are excluded from its requirements. Rod Conference (Symons 1882) provided the code of rules for Justification for this exclusion is given in Annex A of NFPA 780 those who installed lightning protection systems in Britain. and states, "Most electric utilities have standards covering the Following the conference proceeding, the first British code for protection of their facilities and equipment." Therefore, electric the protection against lightning was developed. generating facilities have no guidance on how to implement lightning protection for their facilities. Duke Energy's Fossil Up until this time no guidance was available in the United Hydro Operations Division performed a one to one comparison States for the design and implementation of LPS. There were of the NFPA 780 standard and the IEC 62305 international no texts or standards. Finally, in 1904, following the British standard to determine which of these two standards best met the code, W. S. Lemmon, B. H. Loomis and R. P. Barbour (Lemon lightning protection requirements of its fleet of electric power et al., 1904) prepared "Specifications for Protection of generation facilities. Buildings Against Lightning" which was adopted for American use by the National Fire Protection Association in Quincy MA Keywords— Lightning Protection, Standards, Electric Power Generation Facilities and became the first official standard, issued as NFPA 78, for the design of LPSs. After years of periodic revisions, as more I. INTRODUCTION has been learned about the physics of lightning and with the advancement of technology, this standard is currently issued as The purpose of a lightning protection system (LPS) is to NFPA 780:2017, the standard for the installation of LPSs in the provide an alternate and harmless path for lightning to travel to United States. The scope of this standard provides the earth. Knowing the stated purpose of a LPS, how is requirements for a traditional LPS and list installations for lightning safely and effectively channeled to earth? What which these requirements shall apply. Missing from this list of guidance is provided on how to accomplish this task? Without installations are electric power generation facilities. The an explicit LPS standard, the implementation of LPSs other current NFPA 780 standard excludes electric power generation than those recognized by the international scientific community facilities from its requirements with the assumption that most and approved by the United States National Fire Protection of these facilities have existing standards that address lightning Association (NFPA) or International Electrotechnical protection. Standards, such as IEEE 998: "IEEE Guide for Commission (IEC) lightning protection standards becomes a Direct Lightning Stroke Shielding of Substations", exist that real possibility. Such systems have been refuted by recognized address lightning protection for electrical substations; however, lightning protection authorities, as documented by M. Uman no other United States standard addresses lightning protection and V. Rakov in "A Critical Review of Nonconventional specifically for electric power generation facilities. Therefore, Approaches to Lightning Protection", (American the electric power generation industry has been left to adopt Meteorological Society, 2002), as being no more effective in either NFPA 780, another existing standard, or develop its own the protection of structures or living beings from the effects of LPS standard. lightning than traditional LPSs. Duke Energy’s Fossil Hydro Operations Division, when sections, materials etc.) construction rules. Each LPL is developing its lightning protection criteria for its latest electric assigned a set of maximum and minimum lightning current generation facilities, researched and reviewed existing parameters. The maximum values of the lightning current lightning protection standards for adoption of the one standard parameters for the different LPLs are given and used to derive that would best serve its lightning protection requirements. the physical requirements of lightning protection components Being knowledgeable of both the United States NFPA 780 and (e.g. cross-section of conductors, thickness of metal sheets, the international IEC 62305 standard, Duke Energy performed current capability of surge protection devices, separation a one to one comparison of these two standards when distance against dangerous flash over). The minimum values considering which should be the basis of its lightning define the lightning striking distance for each class of LPL. protection engineering standard. This paper examines Duke Over time, the NFPA 780 standard has relied more and more Energy's evaluation process of these two lightning protection on the IEC 62305 for guidance. Reference to the IEC 62305 standards for the selection of a LPS for its coal, gas, and standard is found throughout the NFPA 780 standard and is hydroelectric generation facilities. even referenced as an acceptable method for conducting a II. DESIGN PHILOSOPHY lightning risk assessment. References cited in the current edition of NFPA 780:2017 to the IEC 62305:2010 standard The 1997 edition of NFPA 780 states that "...lightning is a increased by 50% from the NFPA 780:2014 edition: an stochastic, if not capricious, natural process. Its behavior is not increase from 16 references in the 2014 edition to 24 yet completely understood." Given the incomplete knowledge references in the 2017 edition . of the science of lightning, no LPS can be expected to be 100% effective. A system designed in compliance with any lightning III. RISK ANALYSIS protection standard does not guarantee immunity from damage as lightning is an issue of statistical probabilities and risk Whether or not a LPS is required, and if so, the extent of this system, is determined by the performance of a lightning management. A system designed in compliance with a lightning protection standard should statistically reduce the risk risk analysis study of the structure being protected. The risk R to below a pre-determined threshold. Both NFPA 780 and IEC that lightning damage occurs is the sum of all risk components 62305 provide guidance on the design requirements of their relevant to the particular type of loss. The individual risk respective LPSs, although these standards differ in their components Rx are derived from the following equation: methodology for the implementation of such systems. Rx = (Nx )( Px )( Lx) (1) NFPA 780 is a single, stand-alone standard that provides where Nx is the number of dangerous events, that is, the lightning protection guidance defined by two classes of frequency of lightning strikes causing damage in the area under lightning protection which are based on the physical height of consideration, Px is the probability of damage caused by the structure being protected: Class I protection for structures lightning, and Lx is the loss factor that is the quantitative 75 feet or less in height and Class II for structures greater than evaluation of the damage incurred by the effects of lightning. 75 feet in height. Based on these two classifications, each class is provided a table specifying the material requirements for the The frequency of lightning strikes can be ascertained from respective LPS class. data obtained from the National Lightning Detection Network® (NLDN). From this system the ground flash The IEC 62305 lightning protection standard was created density can be derived. As stated in M. Uman's The Art and by the European TC 81 Technical committee of the IEC and is Science of Lighting Protection, "The two most important and composed of four individual parts: accessible factors in the analysis are the ground flash density IEC 62305-1 : Protection Against Lightning- and the equivalent collective area of the structure and its Part 1:General Principles services ". Data gathered by the NLDN is invaluable in the development of the lightning risk analysis study. IEC 62305-2 : Protection Against Lightning- Part 2: Risk Management A lightning risk analysis study is not a mandatory requirement of the NFPA 780 standard. Instead NFPA 780 IEC 62305-3 : Protection Against Lightning- includes its risk analysis procedure in Annex L, an informative Part 3: Physical Damage to document only and whose information is not a part of its Structures and Life Hazard requirements. Within this Annex, two methods are provided for the determination of lightning risk assessment: a simplified IEC 62305-4 : Protection Against Lightning- risk assessment and a more detailed risk calculation. Part 4: Electrical and
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