Electrical Safety Engineering of Renewable Energy Systems. Rodolfo Araneo

and Ground Resistance6.1 Soil Resistivity Measurements6.2 Wenner Method6.3 Schlumberger Method6.4 Multi-layer Soils6.4.1 Ground Grid in Multi-layer Soil6.4.2 Ground Rod in Multi-layer Soil6.5 Fall-of-Potential Method for Ground Resistance Measurement6.6 Slope Method for Grounding Resistance Measurement6.7 Star-delta Method for Grounding Resistance Measurement6.8 Four Potential Method for Grounding Resistance Measurement6.9 Potentiometer Method for Grounding Resistance Measurement

      12 Appendix 1: Performance of Grounding Systems in Transient Conditions1 Grounding System Analysis2 Mathematical Model3 Computation of Impedances4 Green’s Function4.1 Static Formulation4.1.1 One-Layer Ground4.1.2 Two-Layer Ground4.2 Dynamic Formulation4.2.1 Equivalent Transmission Line Approach5 Numerical Integration Aspects5.1 Singular Term5.2 Sommerfeld Integrals

      13 Appendix 2: Cable Failures in Renewable Energy Systems1 Cable Failures in Renewable Energy Systems: Introduction2 Possible Solutions2.1 Optimal Solutions2.2 Termite Attacks Prevention3 Non-destructive Methods for Cable Testing and Fault-locating3.1 Insulation Resistance (IR) Test3.1.1 IR Measurement of the Cable Insulation (XLPE)3.1.2 IR Measurement of the Polyethylene (PE) Cable Jacket3.2 High-Potential Test3.3 LCR Test3.3.1 Insulation Resistance (IR)3.3.2 Dielectric Absorption Ratio (DAR)3.3.3 Polarization Index (PI)3.3.4 Quality Factor (Q)3.3.5 Dissipation Factor (DF)3.3.6 Time Domain Reflectometry (TDR) Test3.3.7 Arc Reflection (ARC) Test3.3.8 Bridge Methods3.4 Cable Fault Analysis3.4.1 Prelocation3.4.2 Pinpointing4 Sheath and Jacket Repairs5 Termite Baiting Stations and Monitoring6 Termite-proof Cables

      14  Index

      15  End User License Agreement

      List of Illustrations

      1 Chapter 1Figure 1.1 Electric conduction of the heart.Figure 1.2 A normal electrocardiogram (EKG).Figure 1.3 Impedances of the human body.Figure 1.4 Current response of human body to d.c. voltage.Figure 1.5 Internal partial impedances of the human body (no skin contribution).Figure 1.6 Body impedances at 1250 V for a path hand-to-hand vs. the area of contact.Figure 1.7 Temperature–Time Relationship for burns.Figure 1.8 Hemispherical ground-electrode.Figure 1.9 Hyperbolic distribution of the ground-potential....Figure 1.10 Electrode ground-resistance as an equivalent one-port...Figure 1.11 Ground-electrodes in parallel...Figure 1.12 Hemispherical electrodes connected in series.Figure 1.13 Equivalent circuit for the computation of body currents due to a touch voltage.Figure 1.14 Person standing in a region at zero...Figure 1.15 Distribution of the ground-potential with a person standing...Figure 1.16 Distribution of the ground-potential with person standing in a...Figure 1.17 Equivalent circuit for the computation of body currents in the...Figure 1.18 Touch voltage measurement with the current...

      2 Chapter 2Figure 2.1 Single-phase inverter.Figure 2.2 (a) Metal frames and mounting racks of PV arrays and...Figure 2.3 Sun-tracking PV arrays.Figure 2.4 Mounting racks are equipotential to metal frames of...Figure 2.5 Protective devices in combiner box.Figure 2.6 Functionally grounded PV system.Figure 2.7 Functionally grounded system with faulty positive conductor.Figure 2.8 Functionally grounded system with faulty functionally grounded conductor.Figure 2.9 Non-ground-referenced PV system.Figure 2.10 Second Fault in non-ground-referenced PV systems.Figure 2.11 Ground Fault in PV systems.Figure 2.12 Ground Fault Detection Interruption in TN PV systems.Figure 2.13 Defect in the insulation of the grounded conductor.Figure 2.14 GFDI installed in combiner box.Figure 2.15 Faults downstream the PV inverter in ground-referenced PV systems.Figure 2.16 Faults within the inverter.Figure 2.17 Fault occurring at load between inverter and point of common coupling.Figure 2.18 Non- electrically-separated PV system.Figure 2.19 Transformerless PV inverter and ground fault on the a.c. side.Figure 2.20 Transformerless PV inverter and ground fault on the d.c. side.Figure 2.21 Conventional time/current curves describing the effects of d.c. currents.Figure 2.22 Comparison between a.c. and d.c. fibrillation curves.Figure 2.23 Comparison between a.c. and d.c. maximum permissible touch voltages.Figure 2.24 Putting in safety PV generators.Figure 2.25 Array boundary and d.c. voltage requirements.Figure 2.26 Iso-risk curves.

      3 Chapter 3Figure 3.1 Schematics of the grounding system of a PV installation.Figure 3.2 (a) Copper rod manufactured in solid steel and electrolytically copper-plated,...Figure 3.3 Potential distribution of a rod...Figure 3.4 (a) galvanized steel driven-pile connected to the earth system;...Figure 3.5 General representation of a discretized electrode structure (a)...Figure 3.6 Current density distribution over a rod....Figure 3.7 Earth resistance of a ground rod....Figure 3.8 Earth resistance of a ground rod...Figure 3.9 Soil ground potential distribution....Figure 3.10 Two dimensional map of the potential V and the current...Figure 3.11 Comparison between numerical and analytical...Figure 3.12 Ground resistance of different grounding systems...Figure 3.13 Graphs of the ground resistance of a system composed...Figure 3.14 Typical grounding systems of megawatt-sized PV...Figure 3.15 Ground systems of megawatt-sized PV central inverter substations:...Figure 3.16 Ground-grid of a wind farm substation...Figure 3.17 Construction details of a grounding system of a wind farm substation.Figure 3.18 Surface ground potential...Figure 3.19 Definitions of fundamental voltages.Figure 3.20 Sketch of the earthing-systems for circular wind tower foundation slab.Figure 3.21 Grounding system for a square foundation (a) with additional rods (b)...Figure 3.22 Views of the construction of a wind tower.Figure 3.23 General view of an onshore wind farm site.Figure 3.24 Ground resistance of a rectangular ring of shorter side a,...Figure 3.25 Ground resistance (a), prospective touch voltage...Figure 3.26 Ground resistance of a rectangular ring of shorter side a,...Figure 3.27 Prospective touch....

      4 Chapter 4Figure 4.1 Types of lightning flashes comprising (a) cloud-to-ground,...Figure 4.2 Evolution of cloud-to-ground lightning with schematic...Figure 4.3 Types of lightning flashes.112Figure 4.4 Current of a multiple stroke negative downward lightning....Figure 4.5 Short return-stroke current waveform.Figure 4.6 Current (a) and voltage (b) waveforms.Figure 4.7 Rolling sphere method (a) and protective angle method (a-b).Figure 4.8 Main coupling mechanisms: galvanic, inductive and capacitive.Figure 4.9 Main sources of damages.Figure 4.10 Risk components for ground-mounted PV generators.Figure 4.11 Isolated and non-isolated LPS.Figure 4.12 Risk components for rooftop-mounted PV generators.Figure 4.13 Minimum induction loop area.Figure 4.14 SPD in combiner boxes.Figure 4.15 SPD in a central inverter station.Figure 4.16 Three-blade, horizontal axis wind turbine.Figure 4.17 Pictures taken during the construction of a wind tower.Figure 4.18 Lightning protection system over the nacelle.Figure 4.19 LPS of a WT: (a) Lightning path from the blade to the nacelle...Figure 4.20 Equivalent circuit in the case of contact with the down conductor...Figure 4.21 Equivalent collection area of WT.Figure 4.22 Rolling sphere method and Lightning Protection Zones.151Figure 4.23 Equivalent circuit of a horizontal ground electrode.152Figure 4.24 Transient potential rise at the top of a vertical rod under a...Figure 4.25 Frequency behavior of the normalized harmonic impedance...Figure 4.26 Grounding impedance as a function of time.Figure 4.27 Ground-termination system of a WT.

      5 Chapter 5Figure 5.1 Typical MV central collection point.Figure 5.2 Examples of RMU in a wind farm (a) and RMU and CCP in a PV plant (b).Figure 5.3 Radial collection configuration.Figure 5.4 Single-sided ring collection configuration.Figure 5.5 Double-sided ring collection configuration.Figure 5.6 Multi ring collection configuration.Figure 5.7 Star collection configuration.Figure 5.8 RMU (a) and CCP (b) switchgear with trapped-key interlocks.Figure 5.9 Examples of regular PV cluster (a) and irregular wind farm cluster (b).Figure 5.10 Examples of connection with directly buried cables.Figure 5.11 Connection infrastructure of a wind farm: MV connection to the HV/MV...Figure 5.12 Access tracks used for the construction of a wind farm.Figure 5.13 Cable tray with brackets secured to an existing bridge.Figure 5.14 Twisted three-core cable, or triplex.Figure 5.15 General layouts for offshore wind farms: (a)...Figure 5.16 Configurations for the d.c. grid of an offshore...Figure 5.17 Charging modes.Figure 5.18 Plugs: (a) Type 01, (b) Type 2, (c) Type CCS-1, (d) Type CCS-2, (e) CHAdeMO.Figure 5.19 Coordinated LPS and SPD system for EV charging stations.

      6 Chapter 6Figure 6.1 Wenner electrode arrangement. A and B denote the current electrodes,....Figure 6.2 IRIS Syscal Pro equipment.