IEEE Wind Farm Collector System Grounding for Personal Safety Summary of Topics

Content 1.0INTRODUCTION 1.0INTRODUCTION 2.0GENERAL REQUIREMENTS 2.0GENERAL REQUIREMENTS 3.0ENVIRONMENT AND GEOTECHNICAL DATA 3.0ENVIRONMENT AND GEOTECHNICAL DATA 4.0 SOIL RESISTIVITY MODEL 4.0 SOIL RESISTIVITY MODEL 5.0 SAFETY DESIGN CRITERIA 5.0 SAFETY DESIGN CRITERIA 6.0 GROUND FAULT RETURN CURRENT 6.0 GROUND FAULT RETURN CURRENT 7.0 MINIMUM GROUND CONDUCTOR CROSS SECTIONAL AREA 7.0 MINIMUM GROUND CONDUCTOR CROSS SECTIONAL AREA 8.0GROUND ELECTRODE SYSTEM & IMPEDANCE 8.0GROUND ELECTRODE SYSTEM & IMPEDANCE 9.0GROUND POTENTIALS 9.0GROUND POTENTIALS 10.0 DESIGN OF SUBSTATION GROUND GRID AND LIGHTNING PROTECTION 10.0 DESIGN OF SUBSTATION GROUND GRID AND LIGHTNING PROTECTION

1-Introduction This document is a summary of questions/comments on a typical approach for the minimum design requirements of a Wind Power Plant Grounding System. This document is a summary of questions/comments on a typical approach for the minimum design requirements of a Wind Power Plant Grounding System. Aim to Define Topics for Future Standard or Guide Aim to Define Topics for Future Standard or Guide

2 - General requirements 2.1 Definitions: 2.1 Definitions: –Wind Power Plant (WPP) A Wind Power Plant is a single or multiple wind turbine generators electrically interconnected and where the collection system crosses a single or multiple private or public properties; and having one or more points of interconnection to the Utility electric system. –WTG –HV –LV –Grounding system –GPR –Etc..

2.2 Reference Standards and Documents 2.2 Reference Standards and Documents –What reference standards, guides, codes, document to be used ? –ANSI/IEEE 80 Guide for Safety in AC Substation Grounding –ANSI/IEEE 81 Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Ground System –ANSI/IEEE 998 Guide for Direct Lightning Stroke Shielding of Substations –ANSI/ IEEE 367 Recommended Practice for Determining the Electric Power Station Ground Potential Rise and Induced Voltage From a Power Fault –Other IEEE/ANSI?? –National Electrical Code [NEC] –National Electrical Safety Code [NESC] –International Electrotechnical Commission [IEC] –Underwriters Laboratories [UL] –Insulated Cable Engineers Association [ICEA]

2.3 What Consists a WPP Grounding System 2.3 What Consists a WPP Grounding System Interpreting NESC/IEEE 80 –Single point, –Multi point –3 wires ? (Ex. Concentric neutral cable only without additional ground wire –4 wires ? (Ex concentric neutral cable + additional ground wire) –Ungrounded System?

2.4 Grounding Design Tools 2.4 Grounding Design Tools –Grounding Design analysis software and calculation tools. CDEGS ? CDEGS ? CYME ? CYME ? ETAP? ETAP? EPRI ? EPRI ? Other? Other? –Hand Calculation

2.5 Other Design Aspects 2.5 Other Design Aspects –Design Life –Access to Site and Equipment Public, private Public, private –Etc.

3.0Environment and Geotechnical Data 3.1Climate 3.1Climate –Altitude –Normal Ambient Temperature –Extreme Ambient Temperature –Humidity –Max Wind Speed –Precipitation –Seismic Hazard –Lightning Rate

3.2 Geotechnical data 3.2 Geotechnical data –What measurement & why? (Electrical Resistivity; Soil Acidity) –Measurement method? (Wenner, Schlumberger…) –Where? Each WTG location? Each WTG location? Each Junction location? Each Junction location? Each switchgear location (pad or pole mounted) ? Each switchgear location (pad or pole mounted) ? Main Substation ? Main Substation ? Interconnection station ? Interconnection station ? Met tower location ? Met tower location ? Any other location subjected to electrical hazard? Any other location subjected to electrical hazard?

4.0 Soil Resistivity Models Analyse collected data and determine an equivalent soil model for each test location. Analyse collected data and determine an equivalent soil model for each test location. –Uniform soil? –2 layers soil? –More than 2 layers

5.0 Safety Design Criteria In accordance with IEEE 80: 2000 Body Resistanceper IEEE 80: 2000 Body Resistanceper IEEE 80: 2000 Foot Resistanceper IEEE 80: 2000 Foot Resistanceper IEEE 80: 2000 Extra Foot ResistanceApplicable or not applicable ? Extra Foot ResistanceApplicable or not applicable ? Maximum HV Ground Fault Disconnection Time: 0.5s or 1s? Maximum HV Ground Fault Disconnection Time: 0.5s or 1s? Maximum MV Ground Fault Disconnection Time: 0.133s, 0.5s or 1s? Maximum MV Ground Fault Disconnection Time: 0.133s, 0.5s or 1s? System X/R Ratio (default value 20?) System X/R Ratio (default value 20?) Fibrillation Current Calculationper IEEE 80: 2000 & 50kg Body Weight Fibrillation Current Calculationper IEEE 80: 2000 & 50kg Body Weight Starting Surface Layer Resistivity:Per applicable Soil Resistivity Model Starting Surface Layer Resistivity:Per applicable Soil Resistivity Model Surface Layer Thickness Surface Layer Thickness Sub-Surface Layer Resistivity Sub-Surface Layer Resistivity Imported Crushed Rock For Starting Surface Imported Crushed Rock For Starting Surface – 2000 Ω.m wet Electrical Resistivity. Or more than 2000 Ω.m?

6.0 Ground Fault Return Current 1-Phase-to-ground fault current calculations? 1-Phase-to-ground fault current calculations? 2-Phase-to-ground fault current calculations? 2-Phase-to-ground fault current calculations?

6.1 HV Ground fault return current 6.1 HV Ground fault return current –Depends on the Main transformer HV winding connection: Generally Solidly grounded to provide a ground current return path back to the POI through the transformer HV neutral. 6.2 MV Ground fault return current 6.2 MV Ground fault return current –The 34.5kV system neutral is generally solidly connected to ground at the main substation, with no intentional neutral to ground impedance. –Main substation grounding system connection to WTG? –The MV cable screening and bare horizontal ground conductor connection 6.3 LV Ground fault return current 6.3 LV Ground fault return current –The LV system at the WTG with all local metalwork being solidly bonded to the LV Neutral of the WTG Transformer

7.0 Minimum Ground Conductor Cross-section Area Determine the minimum ground conductors cross sectional area (Based on IEEE 80: 2000) (Section , Formula (37) or code tables?) Determine the minimum ground conductors cross sectional area (Based on IEEE 80: 2000) (Section , Formula (37) or code tables?) –Conductor metal –Minimum ground conductor size –Max Ground Ambient temperature –Max Air Ambient temperature –Max bare conductor temperature –Max insulated conductor temperature –System X/R ratio: –HV design total ground fault current (+ Safety margin?) –MV design total ground fault current (+ Safety Margin?) –LV design total ground fault current (+ Safety Margin?) –Fault clearing time ?

8.0Ground Electrode System & Impedance Determine the Ground Electrode System impedance for the wind farm Determine the Ground Electrode System impedance for the wind farm Based on soil resistivity models and ground electrode conductor configurations Based on soil resistivity models and ground electrode conductor configurations –Main S/S & compound What ohmic value? Common sense? What ohmic value? Common sense? –Cable trenches. –Each wind turbine and it’s associated transformer What ohmic value? Common sense? What ohmic value? Common sense? –Each meteorological mast What ohmic value? Common sense? What ohmic value? Common sense? –Each MV junction box/switchgear –etc.

9.0Ground Potentials 9.1GPR, Transfer, Touch & Step Potential 9.1GPR, Transfer, Touch & Step Potential –Examine Ground potential rise due to HV MV & LV ground fault currents. –Compare maximum values to safety criteria for acceptance 9.2Zone of Influence (Hot Zone) Contour 9.2Zone of Influence (Hot Zone) Contour –Determine the Zone of Influence of Ground fault potential (Hot Zone) as per IEEE 367 (and /or local specific code) –Each site shall then be classified based on a 300V Zone of Influence contour limit as recommended by IEEE , section 9.3 as: a “Hot Zone of Influence” GPR >/= 300V. a “Hot Zone of Influence” GPR >/= 300V. a “Cold Zone of Influence”, GPR is < 300V everywhere across the Site. a “Cold Zone of Influence”, GPR is < 300V everywhere across the Site.

10 Design of Substation Ground Grid and Lightning protection 10.1 Base document & references data 10.1 Base document & references data –IEEE 80 – IEEE Guide for Safety in AC Substation Grounding –IEEE 81 – IEEE Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Ground System –IEEE 998 – IEEE Guide for Direct Lightning Stroke Shielding of Substations –The substation location and prevailing keraunic level & ground flash density. –Soil resistivity at all grounding points. –Fault Level Schedule.

10.2 Substation Grounding System 10.2 Substation Grounding System –What design criteria specific to Wind Power Plant? Do we specify a Max Ground Grid Impedance, Why? Do we specify a Max Ground Grid Impedance, Why? What acceptable limits for touch & step potential? (in accordance with IEEE 80). What acceptable limits for touch & step potential? (in accordance with IEEE 80). Fault disconnection time Fault disconnection time minimum ground conductor size & material. minimum ground conductor size & material. Burial depth. Burial depth. Etc.. Etc Substation Lightning Protection 10.3 Substation Lightning Protection –Free standing lightning masts –Lightning rods installed atop substations structures, –Static wire strung between static masts? –Calculation of the Zone of Protection: rolling sphere / electrogeometric method (EGM)/other methods.

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