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TB 675 2017 General guidelines for HVDC electrode design

HVDC electrodes have traditionally been installed on HVDC transmission systems to provide a low resistance current return path during both monopolar and bipolar operation using the earth and/or sea as the conductive medium. HVDC electrodes are in general less costly and have lower losses than dedicated metallic return conductors. Environmental concerns related to electrode operation have become more prominent in recent years due to greater public awareness of potential impacts, tighter environmental approval processes and increasing numbers of HVDC projects. While the environmental approval process can be challenging, the long-time successful operation of older electrodes indicates many of the potential environmental impacts from electrodes can be minimized or eliminated either by suitable selection of the electrode site for impacts remote from the electrode or by application of good design techniques if the impacts are near the electrode or on the electrode site. With the development of new geophysical and geological investigation techniques, and more powerful computer simulation tools for electrical field studies and infrastructure modelling, potentially more economical designs of ground electrodes can be achieved, and the impacts of the electrode operation on existing or potential future infrastructure can be more accurately quantified. This technical brochure is prepared to formalize methodology and guidelines for the analysis, design, construction and testing of new electrodes and refurbishment or extension of existing electrodes. It is a collection of most recent techniques, processes and descriptions of software and procedures available for site selection and electrode designs.

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TABLE OF CONTENTS

EXECUTIVE SUMMARY

CONTENTS

TERMS AND DEFINITIONS

1.  HVDC CONFIGURATIONS WITH GROUND RETURN CURRENT

2.  TYPES OF ELECTRODES AND SELECTION OF TYPE OF ELECTRODE

   2.1  TYPES OF ELECTRODES

   2.2  ELECTRODE SHAPES AND CONFIGURATIONS

      2.2.1 Land Electrodes

      2.2.2 Sea Electrodes

      2.2.3  Beach Electrodes

      2.2.4  Pond Electrodes

   2.3  SELECTION OF ELECTRODE TYPE

3.  ELECTRODE SITE SELECTION CRITERIA AND PROCESS

   3.1  GENERAL ASPECTS OF SITE SELECTION

      3.1.1  Process of Finding Candidate Electrode Locations

      3.1.2  Site Exclusion Process

   3.2  TECHNICAL, ECONOMIC AND TIME ASPECTS OF SITE SELECTION

      3.2.1  Duration of Operation in Monopolar Mode

      3.2.2  Rated and Overload current

      3.2.3  Converter Station Locations

      3.2.4  Line Servitudes or Right-of-way and Land Acquisition

      3.2.5  Environmental and Other Permits

      3.2.6  Possible Impact on Infrastructure

      3.2.7  Constructability and Accessibility

      3.2.8  Permitted Potentials and Potential gradients

   3.3  GEOPHYSICAL, GEOLOGICAL AND HYDROLOGICAL ASPECTS OF SITE SELECTION

      3.3.1  Land Electrodes

      3.3.2  Sea and Shore electrodes

   3.4  PROCESS OF GEOPHYSICAL AND GEOLOGICAL INVESTIGATIONS

      3.4.1  Geoscientific Desktop Study and Definition of Candidate Areas

      3.4.2  Initial Resistivity Model

      3.4.3 Initial Field Investigations

      3.4.4 Site Selection

      3.4.5 Permitting, Land Acquisition, Line Servitudes

      3.4.6  Detailed Field Investigations

      3.4.7 Detailed Resistivity Model

      3.4.8 Preliminary Design and Electrode Modelling

      3.4.9 Borehole Investigations

      3.4.10  Test Electrodes

4.  IMPACTS OF ELECTRODES

   4.1  INTRODUCTION

   4.2  IMPACTS ON INFRASTRUCTURE

      4.2.1  Impacts on Buried Metallic Objects

   4.3  IMPACTS ON THE ENVIRONMENT

      4.3.1  Compass Deflection

      4.3.2  Chemical Aspects

   4.4  IMPACT STUDIES

      4.4.1  Data for Impact Studies

      4.4.2  Physical Variables to Study

5.  ELECTRODE DESIGN ASPECTS

   5.1  GENERAL DESIGN CONSIDERATIONS

      5.1.1  Safety Requirements for Humans and Animals

      5.1.2  Safety Metrics and Criteria

      5.1.3  Physical design criteria and constraints

      5.1.4  Potential Impacts on Environment and Infrastructure

      5.1.5  Constructability

      5.1.6  Data Required for design

   5.2  DESIGN METHODOLOGY

      5.2.1  Simple Calculations

      5.2.2  Simulations

      5.2.3  Verification of Design

   5.3  LAND ELECTRODES

      5.3.1  Design Considerations

      5.3.2  Operation and Maintenance Considerations

      5.3.3  Land Electrode Design Example

   5.4  SEA ELECTRODES

      5.4.1  Design Considerations

      5.4.2  Operation and Maintenance Considerations

      5.4.3  Environmental Impact

      5.4.4  Chemical Aspects

      5.4.5  Structure and Features

      5.4.6  Electrode active element materials

      5.4.7  Sea Electrode Designs

      5.4.8  Sea Electrodes in Operation

   5.5  SHORELINE POND ELECTRODES

      5.5.1  Design Consideration

      5.5.2  Operation and Maintenance Considerations

      5.5.3  GPR, Potential Gradient and Resistance to Remote Earth

      5.5.4  Pond Electrode Examples

   5.6  SHORELINE BEACH ELECTRODES

      5.6.1  Design considerations

      5.6.2  Beach Electrode Example

6.  CONNECTION FROM CONVERTER STATION TO ELECTRODE STATION

   6.1  OVERHEAD ELECTRODE LINES

   6.2  CABLE ELECTRODE LINE

   6.3  DESIGN FACTORS FOR OVERHEAD ELECTRODE LINES

      6.3.1  Factors which affect the overhead electrode line

      6.3.2  Environmental Impact of Overhead Electrode Lines

   6.4  ELECTRODE LINE MONITORING AND PROTECTION

   6.5  MAINTENANCE OF ELECTRODE LINES AND CABLES

7.  AUXILIARY SYSTEMS FOR ELECTRODE STATIONS

   7.1  INTRODUCTION

   7.2  STATION SERVICE SUPPLY

   7.3  ELECTRODE SITE MONITORING SYSTEM

   7.4  FENCES, EQUIPMENT AND CONTROL BUILDINGS

8.  TESTING AND COMMISSIONING

   8.1  LAND ELECTRODE

      8.1.1  Soil Temperature

      8.1.2  Soil Moisture

      8.1.3  Resistance Measurements

      8.1.4  Sub Electrode Resistance

      8.1.5  Current Distribution Measurements

      8.1.6  Potential and Gradient Measurements

      8.1.7  Test of Data Acquisition System

      8.1.8  DC Current in Converter or Power Transformer Neutrals

   8.2  SEA ELECTRODES

   8.3  SHORELINE POND ELECTRODES

   8.4  SHORELINE BEACH ELECTRODES

9.  REFERENCES