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TB 609 2015 Study of Converter Transients Imposed on the HVDC Converter Transformers

The LCC HVDC converter transformers are connected between the AC system and the HVDC converter. A converter transformer is subjected to voltage and current transients as a result of normal converter operation and the faults on the converter side. This document identifies the voltage and current transients imposed by the converter that must be taken into account by the transformer designer.

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TABLE OF CONTENTS

Introduction

      1.1 Review of Previous Work

      1.2 Summary of Transformer Failure Survey

      1.3 Scope of Work

      1.4 References

2. Normal Operation

      2.1 Overview of LCC System

      2.2 Six Pulse Bridge

      2.3 Converter Configurations

            2.3.1 Single 12 Pulse Converters per Pole

            2.3.2 Two 12 Pulse Converters per Pole

      2.4 Voltage Waveforms on the Valve Side of Converter Transformer Terminal

            2.4.1 Operation at 15 Degrees Firing Angle

            2.4.2 Operation at 30 Degrees Firing Angle

            2.4.3 Operation at 90 Degrees Firing Angle

      2.5 Transient Stresses during Commutation

      2.6 Spectral Analysis of Voltage Waveforms

      2.7 References

3.Transformer Stresses Caused by Commutation Failure

      3.1 Commutation

      3.2 Commutation failure Causes

      3.3 Commutation Failure Scenario

      3.4 Transformer Stresses

            3.4.1 Description

            3.4.2 Simulation Results

      3.5 Measurement Results

      3.6 References

4. Polarity Reversal

      4.1 Introduction

      4.2 DC Line Faults

            4.2.1 Response of Normal Control Action

            4.2.2 Fault Detection

            4.2.3 Deionization

            4.2.4 Overshoot of Direct current

      4.3 Polarity Reversal Due to Power Reversal

      4.4 Voltage Distribution during Polarity Reversal

      4.5 Investigation of Polarity Reversal Stresses

            4.5.1 Polarity Reversal during DC Line Faults

      4.6 References.

5. Current Harmonics

      5.1 Introduction

      5.2 Six Pulse Bridge Currents

      5.3 Characteristic AC Harmonics in Line Currents of a Converter transformer

            5.3.1 Characteristic AC Harmonics in Line Current on Valve Side of a Six Pulse Bridge

            5.3.2 Characteristic AC Harmonics in Line Current on Network Side of a Six Pulse Bridge

      5.4 Characteristic AC Harmonics in Line Currents on Valve Side of a Six Pulse Bridge With commutation Reactance

      5.5 Non Characteristic Harmonics

      5.6 Effect of Harmonics on Converter Transformers

      5.7 Level of Harmonics for Transformer Specification

      5.8 Estimation of Losses

            5.8.1 IEC Method

            5.8.2 IEEE Method

      5.9 Temperature Rise Test

      5.10 DC Current in converter Transformer

      5.11 References

6. Simulation Results

      6.1 Introduction

      6.2 Gui-Guang I System

            6.2.1 Operation at 15 Degrees Firing Angle

            6.2.2 Operation at 30 Degrees Firing Angle

            6.2.3 Operation at 90 Degrees Firing Angle

            6.2.4 DC Line Fault

            6.2.5 Commutation Failure

      6.3 Itaipu System

            6.3.1 Operation at 15 Degrees Firing Angle

            6.3.2 Operation at 30 Degrees Firing Angle

            6.3.3 Operation at 90 Degrees Firing Angle

            6.3.4 DC Line Fault

      6.4 Harmonic Content of Transformer Valve Side Voltage in Steady State Operation

            6.4.1 Harmonics in Phase to Ground Voltages

            6.4.2 Harmonics in Phase to Phase Voltages

      6.5 References

7. Field Measurements

      7.1 Gui-Guang I Project (+/- 500kV, 3000MW)

            7.1.1 Steady State Operation

            7.1.2 DC Line fault Test

            7.1.3 Commutation Failure Test

      7.2 Itaipu Bipole (+/- 600 kV, 3150MW)

            7.2.1 Rectifier Normal Operation

            7.2.2 Inverter Normal Operation

            7.2.3 Inverter Commutation Failure on an AC system Fault

            7.2.4 Detailed Comparison of Field Measurements and Simulations

      7.3 Nelson River Bipole 2 (+/- 500kV, 2000MW)

      7.4 Nelson River Bipole 1 (+/- 463.5kV, 1854MW)

            7.4.1 Pole 2 Rectifier -DC Line fault

            7.4.2 Pole 1 Inverter - Commutation Failure

      7.5 Commutation Transients

8. Overview of Existing Transformer Test Requirements

      8.1 Valid Standards

      8.2 Dielectric Tests

            8.2.1 Dielectric Tests on AC Line Winding

            8.2.2 Dielectric Tests on Valve Winding

      8.3 Thermal Tests

      8.4 Ongoing Work with the Standards

      8.5 Comparison of Stress in Service and Stress in Test

      8.6 References

9. Analysis and Conclusions

      9.1 Introduction

      9.2 Normal Operation

      9.3 DC Voltage Polarity Reversal

      9.4 Commutation Failures

      9.5 Current Harmonics

      9.6 Conclusions

      9.7 References