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TB 553 2013 B4-47 Special Aspects of AC Filter Design for HVDC Systems

This new TB is intended as an Addendum to the 1999 Technical Brochure 139 "Guide to the Specification and Design Evaluation of AC Filters for HVDC Projects", which was subsequently converted into IEC/TR 62001. It addresses four areas which continue to be problematic and controversial: a.c. network harmonic impedance, preexisting harmonics, a.c.-d.c. harmonic interaction, and current-based interference criteria. As well as making recommendations, it attempts to inform and explain, so that project-specific decisions can be made with full knowledge of the technical background while balancing the risks and benefits appropriately.

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TABLE OF CONTENTS

1 INTRODUCTION AND OBJECTIVES

      1.1 Introduction

      1.2 Definitions

      1.3 Issues

      1.4 Scope

2 AC NETWORK IMPEDANCE MODELLING

      2.1 Introduction

      2.2 Implications of inaccurate definition of network impedance

      2.3 Considerations for network modelling

      2.4 Network harmonic impedance envelopes

      2.5 Methods of determining envelope characteristics

      2.6 Examples of the impact of different network impedance representations

      2.7 Interharmonic impedance assessment

      2.8 Measurement of network harmonic impedance

      2.9 Conclusions

      Appendix 2.1 Location of worst case network impedance

      Appendix 2.2 Accuracy of network component modelling at harmonic frequencies

3 PRE-EXISTING HARMONICS

      3.1 Introduction

      3.2 Modelling and measurement of pre–existing harmonic levels

      3.3 Harmonic performance evaluation, methods and discussion

      3.4 Calculation of total harmonic performance indices

      3.5 Harmonic rating evaluation

      3.6 Difficulties with the voltage source/worst network model for rating

      3.7 Further possible calculation procedures for rating evaluation

      3.8 Conclusions

      Appendix 3.1 Further guidance for the measurement of harmonic voltage distortion

      Appendix 3.2 Project experience of pre-existing harmonic issues

      Appendix 3.3 Worked examples showing impact of pre-existing distortion

      Appendix 3.4 Comparison of calculation methods

4 HARMONIC INTERACTION ACROSS CONVERTERS

      4.1 Introduction

      4.2 Practical experience of problems

      4.3 Indicators of where harmonic interaction is significant

      4.4 General overview of modelling techniques

      4.5 Composite resonance

      4.6 Core saturation instability

      4.7 Particular considerations for back–to–back converters

      4.8 Issues to be considered in the design process

      4.9 Parallel a.c. lines and converter transformer saturation

      4.10 Recommendations for Technical Specifications

      4.11 Conclusion

5 CURRENT-BASED INTERFERENCE CRITERIA

      5.1 Introduction

      5.2 Determining the necessity for telephone interference limits

      5.3 Defining telephone interference limits

      5.4 Consequences for filter design

      5.5 Telephone infrastructure mitigation options

      5.6 Experience and examples

      5.7 Conclusions

      Appendix 5.1 Example of induced noise calculation with Dubanton equations

      Appendix 5.2 Illustration of the benefit of including a TIF requirement in the Technical Specification

      Appendix 5.3 The impact of a.c. network harmonic impedance and voltage level on the filter design

                          necessary to fulfil an IT criterion

      Appendix 5.4 Specification of IT limits dependent on network impedance

6 REFERENCES