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TB 269 2005 SC B4 WG B4.37 VSC Transmission

This Brochure describes VSC Transmission technology, i.e. HVDC transmission using Voltage Sourced Converters. A comparison with Line Commutated HVDC technology is provided. The WG found no technical reason why this technology could not be used at high voltage and power, and concluded that such development would depend solely on the perceived commercial return on the R&D investment.

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TABLE OF CONTENTS

1. DEFINITIONS

      1.1 INTRODUCTION

      1.2 LIST OF LETTER SYMBOLS

      1.3 GENERAL TERMS RELATED TO CONVERTER CIRCUITS AND POLE TOPOLOGIES FOR

           VSC CIRCUITS

            1.3.1 VSC Transmission

            1.3.2 VSC Phase Unit

            1.3.3 VSC Unit

            1.3.4 VSC Substation

            1.3.5 Two-Level Converter

            1.3.6 Three-Level Converter

            1.3.7 Multi-Level Converter

            1.3.8 VSC Pulse Number p

      1.4 VSC UNIT EQUIPMENT

            1.4.1 VSC Valve

            1.4.2 Diode Valve

            1.4.3 VSC Valve Level

      1.5 VSC SUBSTATION EQUIPMENT

            1.5.1 Interface Transformer

            1.5.2 Phase Reactor

            1.5.3 VSC DC Capacitor

      1.6 REFERENCES

2. VSC TRANSMISSION APPLICATIONS

      2.1 INTRODUCTION

      2.2 EXAMPLES OF POSSIBLE VSC TRANSMISSION APPLICATIONS

      2.3 THE VOLTAGE SOURCE CONVERTER AS A BLACK BOX

      2.4 THE PRINCIPLES OF ACTIVE AND REACTIVE POWER CONTROL

            2.4.1 The Principle of Active Power Control

            2.4.2 The Principle of Reactive Power Control

            2.4.3 Basic PQ Diagram for a VSC Station

      2.5 OPERATING PRINCIPLES OF A VSC TRANSMISSION SCHEME

      2.6 LOSSES

      2.7 SUMMARY OF THE BASIC CHARACTERISTICS OF VSC TRANSMISSION

      2.8 REFERENCES

3. BASIC OPERATING PRINCIPLES OF VSC TRANSMISSION

      3.1 INTRODUCTION

      3.2 BASIC OPERATING PRINCIPLES OF TWO-LEVEL CONVERTERS

      3.3 TWO-LEVEL VSC—THREE-PHASE CONFIGURATION

            3.3.1 Terminal Voltages

            3.3.2 Fundamental Frequency Equations—Square Wave Operation

      3.4 ACTIVE AND REACTIVE POWER EQUATIONS

      3.5 VSC CONTROL AND HARMONICS

      3.6 REFERENCES

4. VSC TRANSMISSION TOPOLOGIES

      4.1 INTRODUCTION

      4.2 CONVERTER PHASE UNIT TOPOLOGIES

            4.2.1 Converter Phase Unit Topologies—General Aspects

            4.2.2 Two-Level Converter

            4.2.3 Three-Level Neutral Point Clamped Converter

            4.2.4 Multi-Level Neutral Point Clamped Converter

            4.2.5 Three-Level Floating Capacitor Topology

            4.2.6 Multi-Level Capacitor Topology

      4.3 COMBINATION OF CONVERTER PHASE UNITS

            4.3.1 General

            4.3.2 Combination Using Separate Transformer Windings

                  4.3.2.1 Series Connection of Converters

                  4.3.2.2 Parallel Connection of Converters

                  4.3.2.3 Series and Parallel Connection on the DC Side

      4.4 CONCLUDING DISCUSSION

            4.4.1 Converter Phase Unit Topologies

            4.4.2 Combination of Converter Units

      4.5 REFERENCES

5. VSC TRANSMISSION VALVES

      5.1 INTRODUCTION

      5.2 SEMICONDUCTORS FOR VSC TRANSMISSION

            5.2.1 Overview of High Power Semiconductors

            5.2.2 Thyristors

            5.2.3 GTOs and IGCTs (GCT)

            5.2.4 IGBT Type Devices

            5.2.5 Comparison of Devices

      5.3 VSC VALVE DESIGN CONSIDERATIONS

            5.3.1 Reliability (IGBT)

            5.3.2 IGBT Current Rating

            5.3.3 Transient Current Requirements

            5.3.4 Diode Requirements

      5.4 THERMAL DESIGN

            5.4.1 Converter Power Losses

            5.4.2 Cooling System Design

            5.4.3 IGBT Losses

            5.4.4 Voltage Rating

                  5.4.4.1 Aspects of Series Connection

                  5.4.4.2 Commutation Process

      5.5 MECHANICAL STRUCTURE OF THE VALVE

      5.6 VALVE HALL OR VALVE ENCLOSURES

      5.7 REFERENCES

6. OTHER MAIN EQUIPMENT FOR VSC TRANSMISSION SCHEMES

      6.1 INTRODUCTION

      6.2 POWER COMPONENTS OF A VSC TRANSMISSION SCHEME

      6.3 VSC SUBSTATION CIRCUIT BREAKER

      6.4 AC SYSTEM SIDE HARMONIC FILTERS

      6.5 RADIO FREQUENCY INTERFERENCE FILTERS

      6.6 INTERFACE TRANSFORMERS AND PHASE REACTORS

      6.7 CONVERTER SIDE HARMONIC FILTERS AND HF BLOCKING FILTER

      6.8 VSC DC CAPACITOR

      6.9 DC FILTER

      6.10 NEUTRAL POINT GROUNDING BRANCH

      6.11 DC REACTOR

      6.12 COMMON MODE BLOCKING REACTOR

      6.13 DC CABLE AND OVERHEAD TRANSMISSION LINES

      6.14 SPECIAL ASPECTS FOR BACK-TO-BACK DC TRANSMISSION SYSTEMS

      6.15 REFERENCES

7. VSC CONTROL

      7.1 INTRODUCTION

      7.2 MODES OF CONTROL

            7.2.1 AC Voltage Control

            7.2.2 Power Control

            7.2.3 Reactive Power Control

            7.2.4 DC Voltage Control

            7.2.5 Current Control

            7.2.6 Frequency Control

      7.3 INFORMATION REQUIREMENTS FOR CONTROLS

      7.4 PERFORMANCE OF CONTROLS

      7.5 LEVELS OF CONTROLS

            7.5.1 Firing Control

            7.5.2 Converter Unit Control

            7.5.3 System Control

      7.6 COORDINATION OF CONTROLS

            7.6.1 Supply to a Load with No Other Source of Generation

            7.6.2 Interconnection of Two or More AC Power Systems

            7.6.3 Telecommunication Between Converter Stations

            7.6.4 Supply from a Wind Farm

      7.7 REFERENCES

8. FAULT PERFORMANCE AND PROTECTION REQUIREMENTS

      8.1 PROTECTION SYSTEM PHILOSOPHY

      8.2 TYPE OF PROTECTION AND FAULT CLEARING ACTIONS

      8.3 VSC SUBSTATION PROTECTION

      8.4 INTERNAL FAULTS IN THE VSC SUBSTATION

            8.4.1 Internal AC Bus Fault

            8.4.2 DC Bus Fault

            8.4.3 Component Failure

                  8.4.3.1 VSC Valve Failure

                  8.4.3.2 DC Capacitor Failure

                  8.4.3.3 Phase Reactor Failure

      8.5 EXTERNAL FAULTS AND SWITCHING TRANSIENTS ON THE AC SIDE

            8.5.1 AC Voltage Dip

            8.5.2 AC Temporary Overvoltage

            8.5.3 AC Lightning Overvoltage

            8.5.4 AC Switching Overvoltage

            8.5.5 AC Voltage Phase Shifting

            8.5.6 AC Voltage Phase Unbalance

            8.5.7 DC Overvoltage

            8.5.8 Post-Fault Recovery

      8.6 FAULTS ON THE DC TRANSMISSION LINE OR CABLE

            8.6.1 DC Cable Fault

            8.6.2 DC Overhead Line Fault

            8.6.3 DC Bus Overvoltage (dc overhead line only)

            8.6.4 DC Overvoltage

            8.6.5 Other Protection Measures

      8.7 REFERENCES

9. HARMONIC PERFORMANCE

      9.1 INTRODUCTION

      9.2 WAVE DISTORTION

      9.3 FUNDAMENTAL AND HARMONICS

            9.3.1 Three-Phase 2-Level VSC

            9.3.2 Pulse Width Modulation (PWM)

            9.3.3 Multi-Pulse and Multi-Level Converters

            9.3.4 Comparison of the Harmonic Content at the AC Terminals of the VSC Valve Units

      9.4 HARMONIC VOLTAGES ON POWER SYSTEMS DUE TO VSC OPERATION

      9.5 DESIGN CONSIDERATIONS FOR HARMONIC FILTERS (AC SIDE)

      9.6 DC SIDE FILTERING

      9.7 REFERENCES

10. ENVIRONMENTAL IMPACT

      10.1 INTRODUCTION

      10.2 AUDIBLE NOISE

      10.3 VISUAL IMPACT

      10.4 ELECTRIC AND MAGNETIC FIELDS (EMF)

      10.5 ELECTROMAGNETIC COMPATIBILITY (EMC)

      10.6 REFERENCES

11. APPLICATION STUDIES

      11.1 INTRODUCTION

      11.2 FEASIBILITY STUDIES

            11.2.1 Economic Justification of a VSC Scheme

            11.2.2 Comparing Alternative Termination Points for the VSC Scheme

            11.2.3 Comparing the Selected Scheme with Alternative Solutions

            11.2.4 Preparing an Outline Specification of the VSC Transmission Project

      11.3 SPECIFICATION STUDIES

            11.3.1 Specifying the Performance Requirements for the VSC Scheme

            11.3.2 AC System Data for the Design of the VSC Scheme

      11.4 IMPLEMENTATION STUDIES

      11.5 MODELLING OF THE VSC SCHEME

            11.5.1 Load Flow Modelling Requirements

            11.5.2 Short-Circuit and Harmonic Modelling Requirements

            11.5.3 Electromechanical Stability Modelling Requirements

            11.5.4 Electromagnetic Transient Modelling Requirements

      11.6 REFERENCES

12. TESTING AND COMMISSIONING

      12.1 INTRODUCTION

      12.2 THE TESTING AND COMMISSIONING PROCESS

      12.3 FACTORY TESTS

            12.3.1 Component Tests

            12.3.2 Control System Tests

      12.4 SITE TESTS (COMMISSIONING)

            12.4.1 General

            12.4.2 Precommissioning Tests

            12.4.3 Subsystem Tests

            12.4.4 System Tests

                  12.4.4.1 High-Voltage Energisation

                  12.4.4.2 Converter Operational Tests

                  12.4.4.3 Transmission Tests

            12.4.5 Trial Operation

            12.4.6 Acceptance Tests

      12.5 REFERENCES

13. LIFE CYCLE COST

      13.1 INTRODUCTION

      13.2 DETERMINATION OF THE PROFITABILITY OF AN INVESTMENT

      13.3 LIFE CYCLE COSTING

            13.3.1 Operational Life

            13.3.2 Interest and Inflation Rates—Calculation of Present Value

            13.3.3 Initial Costs of the System

            13.3.4 Cost of Spare Parts

            13.3.5 Annual Costs of System Losses

            13.3.6 Cost of Periodic Refurbishment

            13.3.7 Annual Operating Costs of the System

            13.3.8 Annual Maintenance Costs of the System

            13.3.9 Annual Cost of Unavailability

            13.3.10 Salvage Value or Disposal Costs of VSC Transmission Systems

                  13.3.10.1 Salvage Value

                  13.3.10.2 Disposal Cost

      13.4 BENEFITS OF CONTROLLABILITY

      13.5 REFERENCES

14. COMPARISON OF LINE COMMUTATED CONVERTER AND VSC

      14.1 INTRODUCTION

      14.2 DIFFERENCES RESULTING FROM THE COMMUTATION PRINCIPLE

            14.2.1 Dependence on an AC Voltage Source

            14.2.2 Reactive Power Consumption or Generation

            14.2.3 Short-Circuit Level Requirement for Stable Operation

            14.2.4 Harmonics and Filter Requirements

            14.2.5 Overvoltages in the AC System

            14.2.6 Robustness against AC System Faults

      14.3 DIFFERENCES RESULTING FROM THE SOURCE TYPE

            14.3.1 Protection against DC System Faults

            14.3.2 Flexibility of the Power Flow Reversal in the Multi-Terminal HVDC System

            14.3.3 Cost, Losses, Reliability and the Availability of the Large Scale HVDC System

      14.4 SUMMARY

      14.5 REFERENCES

15. VSC TRANSMISSION OUTLOOK

      15.1 INTRODUCTION

      15.2 FUTURE TRENDS

            15.2.1 Reliability

            15.2.2 Capital Cost of a VSC Transmission Installation

            15.2.3 Controllable Switching Components

            15.2.4 Power Losses

            15.2.5 Increased DC Voltage and Power Rating of DC Extruded Cables

            15.2.6 Utilisation of the Functionality and Controllability of VSC Transmission

      15.3 REFERENCES

16. CONCLUSION