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Alltec Lightning Risk Analysis

In many situations the need for lightning protection is critical due to the severe consequences that could result from an unprotected lightning strike. The National Fire Protection Association (NFPA)-780 and the International Electrotechnical Commission (IEC)-62305 standards refer to lightning risk analysis in order to establish a technical compliance base for selection of levels and requirements of lightning protection systems.

The National Fire Protection Association (NFPA)-780 2014 editions has options for both simplified and detailed lightning risk analysis. A simplified lightning risk analysis only determines whether a particular structure(s) located at the specific area will require a lightning protection system to be installed or not. Simplified lightning risk analysis does not determine the level of lightning protection system.

Meanwhile, the detailed lightning risk analysis provided in NFPA-780 2014 is a sub-set of the detail analysis presented in the IEC 62305-2 standard. NFPA-780 Annex “L” mentions “continuity of facility service” as one of the major consequences for a simplified risk analysis, however, no specific loss component values are referenced in the detailed risk analysis for any facility where continuity of service is required.

Alltec’s Capability

Alltec has the capability to perform Lightning Risk Analyses in compliance to both the NFPA-780 and IEC 62305 standards. Alltec’s Lightning Risk Analysis consists of investigation of the facilities, review of proper documentation, and planning in order to identify the risks associated with lightning and the measures taken to reduce the risks.

The types of risk due to lightning for a particular structure or facility could include one or more of the following:

  • R1 risk associated with loss of life or injury
  • R2 risk associated with loss of service
  • R3 risk associated with loss of historical significance
  • R4 risk associated with loss of economical value

The analysis requires review of the physical site to identify zones of activities. Even if the risk of touch and step voltages due to flashes to the structure is minimal, it is necessary to evaluate at least two zones: an external and internal for each structure. The risk analysis should identify for each considered zone:

  • The characteristics of that zone;
  • The existing internal systems;
  • The relevant lightning risks components to consider;
  • The value of loss

It is also necessary to provide input data for incoming lines in the structures at the facility; the characteristics that influence the number of surges caused by lightning on the line and that may be dangerous for the internal systems of the structure to which the line is connected. The basic parameters noted are:

  • Length and resistivity of the soil for underground cables;
  • Shield resistance of the underground cables (if any);
  • Height and shield resistance of the overhead cables
  • Protection measures provided at point of entry of line in the structure;

Lines having the same routing shall be considered as a unique line; in this case the line with the most unfavorable characteristics, from the point of view of surges, is to be indicated (in other words, the one transmitting the most dangerous surges for internal systems of the structure to which it is connected), as indicated in following table:

Risk of surge damage as related to line characteristics

Less Dangerous

More Dangerous

Underground Cable Overhead
Shielded Not Shielded
High impulse withstand voltage level Reduce impulse withstand voltage levels
Supplied with HV/LV Transformer Not supplied with HV/LV transformer
SPD at point of Entry of Line No SPD at Point of Entry of Line
Optical Fiber Co-axial Cable

Our Lightning Risk Analysis Tool

Alltec Engineers use specialized analysis tools to perform detailed lightning risk analyses associated with sites. All required input data should be collected as per the standard.  Each Risk component is evaluated as per the standard and the total associated risk is calculated. The total risk is compared to the Tolerable Risk Value.

Lightning_Assesment_Article_1An example of the Calculated Risk. The Total Risk is higher than tolerable risk value, indicating the facility requires lightning protection system

The selection of the most suitable protection measures is made according to the share of risk components and according to the technical and economic aspects of the different protection measures. Typically, this type of risk analysis requires a detailed dialog between Alltec Engineers and the client, resulting in a highly customized and useful analysis. The major protection measure parameters include:

  • Lightning Protection System and associated level
  • Surge Protection Device (SPD) at Line Entrance
  • Coordinated SPDs
  • Shielding of cables/wiring configuration and equipment withstand voltage
  • Touch and Step Voltage criterion
  • Type of surface.

Lightning_Assesment_Article_2An example of the Calculated Risk after selection of protection measures (Lightning Protection System, Level III and Coordinated Surge Protection Devices). The Total Risk is lower than tolerable risk value, indicating the facility is acceptably protected

Applications

For example Alltec has performed detailed lightning risk analyses for major petrochemical and solar facilities.

One petrochemical facility is located in the Upper Midwestern United States. Structures within the petrochemical facility were classified under both flammable and nonflammable zones. Typical structures include operations building, fire pump building, MCC buildings, tank farm area, rail loading area, and pump pad transfer area. The detailed lightning risk analysis was performed for each structure. Based on the selection of risk assessment parameters, lightning protection was recommended for the structures which were under flammable zone classification. The balance of the non-critical structures did not require to have installed lightning protection systems.

Corresponding to the lightning risk assessment results, Alltec provided code compliant structural lighting protection system solutions for the needed structures. The solution set included recommendations for the cascaded application of Surge Protection Devices (SPD) with review of electrical single line diagrams.

One of the solar facilities is located in the Southeastern US. The solar facility was divided into various zones including ground mounted solar panel arrays, PCS stations, Photovoltaic Combining Switchgear (PVCS) stations, weather stations, and operations buildings. The risk associated with loss of service should be considered when determining the need for an effective lightning protection system for any solar facility.

In any instance where possible damage to any installed system (either ground mounted solar panel units and/or inverter station/PVCS stations) is considered as “unacceptable loss of service”, it is recommended that the International Electrotechnical Commission (IEC) 62305- 2010-2 should be considered to select the typical loss values for power supply. Alltec Lightning Risk Assessments for large solar array panels with multiples inverters and PVCS stations reflects the necessity of an effective lightning protection system to provide for 100% continuous service from all installed components.

To try our Lightning Risk Analysis Tool please visit: alltecglobal.com/resources/lightning-risk-assessment. Call +1 (828) 646-9290 or email info@alltecglobal.com for more information. You can also send a message through our online contact form alltecglobal.com/contact.

 

Rev. 20151210

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