The Lightning Rod as a Danger

Description

This book investigates the physical effects of a lightning flash on a person near the down conductor of a lightning protection system. These effects are the touch voltage, the step voltage and the side flash. For this purpose, a full-scale simulation model of the human body with a resistance of 1000 ohms was first created. In the simulation model, the body can touch the down conductor or be placed close to it. Furthermore, the specific resistance of the earth is varied. Likewise, insulating layers such as asphalt can be incorporated into the simulation model. Also, special cases like water permeable layers or water layers on an asphalt layer can be calculated. In post-processing, all relevant values can be determined, such as the energy converted in the body, the charge, the current and the voltage applied to the body. A comparison with the permissible limit values then shows for the lightning protection classes whether there is danger or not and provides information on necessary measures. There is a risk for death and injury if the down conductor is touched. However, there is also a risk of a side flash if a person is standing next to a discharge. Site isolation with dry asphalt is effective, but there is a residual risk of surface discharges. In real situations with wet asphalt, water-permeable layers or asphalt with a water layer, however, there is a great risk of death or injury. Equipotential bonding with an earthing grid is a necessary but not sufficient solution with regard to the induced voltage at negative subsequent stroke. Therefore, the situation must always be examined on a case-by-case basis with regard to the safety requirements. The only effective measure to prevent injury and death due to touch voltage is an insulating down conductor in conjunction with equipotential bonding. The measures for reducing the touch voltage, such as site insulation and equipotential bonding, basically also apply to limiting the step voltage. A risk calculation according to IEC 62305-2 gives the mean time between two events of injury and death MG = 1/RA. The tolerable risk is: RA = 0,0001 or MT = 10.000 years, equivalent to one death in 10.000 years. Preface Acknowledgements About This Book Contents About the Author 1 Introduction 2 Model for Calculating the Hazard 3 Exemplary Buildings with Earthing System Type A and Type B 4 Permissible Limits for the Cause of Death Due to Ventricular Fibrillation 4.1 Permissible Limits for Touch Voltage 4.2 Limit for Step Voltage 5 Materials 6 Danger from Lightning Currents 10/350, 1/200; 0.25/100 According to Type of Coupling 6.1 Galvanic Coupling Caused by a Down Conductor UA 6.2 Galvanic Coupling UE Due to Lightning Current in Soil 6.2.1 Galvanic Coupling UE. Person in Contact with a Down Conductor 6.2.2 Galvanic Coupling UE. No Contact of a Person with the Down Conductor 6.3 Inductive Coupling UM 6.4 Electric Coupling Due to Proximity UN Causing a Possible Side Flash 6.5 Capacitive Coupling 6.6 Electromagnetic Radiation 6.7 Influence of Equipotential Control Measures 6.7.1 Galvanic Coupling UE with a Person in Contact with Down Conductor in Case of Equipotential Control 6.7.2 Galvanic Coupling UE Without a Person in Contact with Down Conductor in Case of Potential Control 6.8 Results 6.8.1 Person in Contact with a Down Conductor in a Distance of 0.8 m 6.8.2 Galvanic Coupling with a Person in Contact with Down Conductor in a Distance of 0.4 m 6.8.3 Results for Inductive Coupling Depending on the Distance of a Person to the Down Conductor 7 Effect of Site Insulation with Asphalt According to IEC 62305-3 7.1 Galvanic Coupling UE with Contact of a Person with the Down Conductor 7.2 Inductive Coupling UM with a Person in Contact with the Down Conductor 7.3 Galvanic Coupling UE Without Contact of a Person with Down Conductor 7.4 Electric Coupling Due to Proximity UN 7.5 Effect of Potential Control with Meshed Earth Grid Underneath of the Asphalt Layer 7.5.1 Effect of Potential Control on Galvanic Coupling 7.5.2 Effect of Potential Control on Inductive Coupling 7.6 Asphalt with a Water Level of 2 cm 7.6.1 Galvanic Coupling UE, Person in Contact with Down Conductor 7.6.2 Galvanic Coupling UE Without Contact of a Person to Down Conductor 7.6.3 Inductive Coupling UM 7.7 Effect of Potential Control Measures Under a Water Covered Asphalt Layer 7.7.1 Effect of Potential Control Measures on Galvanic Coupling 7.7.2 Effect of Potential Control on Inductive Coupling (Person in Contact with Down Conductor) 7.8 Evaluation of the Results of Site Insulation with Asphalt 8 Effect of Site Insulation with Gravel According to IEC 62305-3 9 Water-Permeable Site Insulation 9.1 Water-Permeable Materials 9.2 Effect of a Water-Permeable Layer 9.2.1 Galvanic Coupling UE with a Person in Contact with Down Conductor 9.2.2 Galvanic Coupling UE Without a Person in Contact with Down Conductor 9.2.3 Inductive Coupling UM 9.3 Effect of Potential Control Measures in Case of a Water-Permeable Layer 9.3.1 Effect on Galvanic Coupling 9.3.2 Effect of Inductive Coupling 10 Danger Due to Step Voltage 10.1 Earthing System Type A 10.2 Earthing System Type B 10.3 Comparison of Step Voltage for Earth System Type A and B for Worst Case 10/350 11 Summary of the Hazard Posed by a Lightning Rod 11.1 Danger from Touch Voltage When Touching a Bare Down Conductor 11.2 Danger from Proximity and Step Voltage Without Touching a Bare Down Conductor 12 Measures to Reduce Step and Touch Voltage as Per IEC 62305-3 12.1 Distance 12.2 Site Insulation 12.3 Signage 12.4 Insulation of the Down Conductor 13 Insulating Down Conductor 13.1 Requirements for Insulating Down Conductor 13.2 Electric Field Strength Along an Insulating Down Conductor 13.2.1 Electrical Stress When a Person is in Contact with an Insulating Down Conductor 13.2.2 Electrical Stress When a Person is not Contact with an Insulating Down Conductor 13.3 Type Test of Insulating Down Conductors 14 National and International Statistics of Deaths and Injuries 15 Statistics of Relevant Parameters of Lightning 15.1 Statistics of the Steepness of Current of Negative Cloud to Ground Flashes 15.2 Normative Values in IEC 62305–1 16 Calculation of Risk RA for Death and Injury of Living Beings Due to Electric Shock as a Result of Touch- and Step Voltages According to IEC 62305–2 17 Strength of Air Gaps at Inductive Coupled Surge Voltages 17.1 Experimental Results from Literature 17.2 Calculation of Breakdown Voltage for Ramped Current Rise According to IEC 62305–1 17.2.1 Calculation Methodology 17.2.2 Calculation of the Dangerous Zone for Induced Voltage with Ramp-Shaped Current Rise According to IEC 62305–1 17.3 Calculation of Breakdown Voltage for Induced Voltage (Delta Impulse) 17.3.1 Test Facilities for EMP 17.3.2 Method of Calculation 17.3.3 Calculation of the Dangerous Zone for Induced Voltage (Delta Impulse) 18 Numeric Calculation 18.1 Numeric Field Calculation Using Comsol-Multiphysics and XGS-Lab 19 Applied Pulse Shapes 0.25/100 According to IEC 62305-1 20 Propagation and Velocity of Surface Discharges 20.1 Surface Discharges in Nature 20.2 Theory of Surface Discharges 20.3 Comparison of Surface Discharges on Panels at Lightning Impulse Voltage and Delta-Impulse Voltage 20.3.1 Tests on Panels 20.3.2 Field Calculation for the Test Arrangement Used for Tests 20.4 Surface Discharges on Coaxial Insulating Down Conductors 20.4.1 Estimation of the Leader Inception Voltage 20.4.2 Laboratory Test on a Conductor with XLPE Insulation 21 Annex A: A Contribution to the Limitation of Step Voltages 21.1 State of Art 21.2 Insulation Material 21.3 Calculation with XGS-Lab (Grounding System Analysis) 21.4 Calculation with Comsol Multiphysics 21.5 Calculation Including Soil Ionisation 21.6 Calculated Earthing System 21.7 Convention for the Results of the Calculation 21.8 Step Voltage Without Insulating Layer 21.9 Step Voltage with a Dry, Insulating Layer of 5 cm Asphalt or 15 cm Gravel 21.9.1 Step Voltage with a Wet Layer of Asphalt 21.9.2 Step Voltage with a Wet Layer of Gravel 21.9.3 Step Voltage for a 10 cm High Rain Water Layer on an Insulating Layer of 5 cm Asphalt 21.9.4 Calculation of the Edge Effect on a Dry Asphalt Layer with Comsol-Multiphysics 21.9.5 Calculation with Limited and Sprinkled Asphalt Layer with Comsol-Multiphysics 21.9.6 Technical Solution with Potential Equalisation 21.9.7 Formation of Surface Discharges 21.10 Summary References References