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TB 034 1989 SC 33/14 JWG 33/14.05 Guidelines for the applications of metal oxide arresters without gaps for HVDC converter stations.

This guide for metal oxide arresters without gaps for HVDC converter stations is a supplement to the application guide for insulation coordination and arrester protection of HVDC converter stations published in Electra No.96 (Oct. 1984). It gives basic information about metal oxide material and basic arrester characteristics which will be of value when designing and specifying an arrester protective scheme and specifying the arresters.

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TABLE OF CONTENTS

1 SCOPE

2 METAL OXIDE ARRESTER CHARACTERISTICS

      2.1. Metal oxide material and arrester assemblies

            2.1.1. Voltage-Current characteristics

            2.1.2 Microstructure

            2.1.3 Conduction mechanism

            2.1.4 Degradation of zinc oxide material

            2.1.5 Thermal stability

      2.2. Basic arrester parameters and performance

            2.2.1 Reference voltage of an arrester (Uref)

            2.2.2 Reference current of an arrester

            2.2.3 Nominal discharge current or an arrester

            2.2.4 Residual voltage (discharge voltage) o an arrester (Ures)

            2.2.5 Protection characteristics of an arrester

            2.2.6 Continuous operating voltage

            2.2.7 Continuous current

            2.2.8 Coordinating current

            2.2.9 Discharge duty

            2.2.10 Degradation and acceleration

            2.2.11 Temporary overvoltage withstand versus time characteristics of an

                     arrester

3 ARRESTER SCHEMES AND STRESSES IN HVDC CONVERTER STATIONS

      3.1 Arrester schemes

      3.2. Stresses by continuous operating voltages

      3.3 Stresses by temporary overvoltage

            3.3.1 AC Side generated temporary overvoltage

            3.3.2 DC side generated temporary overvoltage

      3.4 Stresses by transient overvoltage

            3.4.1 Transient stresses on valve arresters (V)

            3.4.2 Transient stresses on the midpoint DC bus arrester (M)

            3.4.3 Transient stresses on the converter OC arrester (CB)

            3.4.4 Transient stresses on the DC bus arrester (DB)

            3.4.5 Transient stresses on the neutral bus arrester (E)

            3.4.6 Transient stresses on the Dc filter arrester (FD)

            3.4.7 Transient stresses on the arrester across the DC reactor (DR)

            3.4.8 Transient stresses on the AC bus arrester (A)

            3.4.9 Transient stresses on the AC filter arrester )FA)

      3.5 Different transmission schemes

4 STUDIES FOR DETERMINATION OF ARRESTER STRESSES

      4.1 General considerations

            4.1.1 Objectives of the studies

            4.1.2 Information assumed to be available

            4.1.3 Study approach

      4.2 Events to be studied and relevant transients

      4.3 Methods for studying different events and representation

            4.3.1 General requirements for system modeling

                  4.3.1.1 Switching type transients and temporary overvoltage

                  4.3.1.2 Steep front and lightning type transients

                  4.3.1.3 Thyristor valve and control and protection modeling

            4.3.3 Required data

            4.3.4 Study tools

                  4.3.4.1 Frequency range up to switching type transients and temporary

                            overvoltage

                  4.3.4.2 Steep front and lightning type transients

            4.3.5 Considerations specific to the study of different transient events

                  4.3.5.1 Faults and switching operation in the AC side

                  4.3.5.2 Ground faults and switching surges in the DC side.

                  4.3.5.3 Events forcing the DC current into arresters

                  4.3.5.4 Lightning overvoltage and over currents

      4.4 Arrester stresses based on study results

      4.5 Studies for expansion of arrester schemes and for replacement of arresters

5 METAL OXIDE ARRESTERS TO LIMIT TEMPORARY OVERVOLTAGE

      5.1 Introduction

      5.2 Basic philosophy

      5.3 Studies to be performed

6 DETERMINATIONS OF ARRESTER CAPABILITIES AND ARRESTER TEST REQUIREMENTS

      6.1 Introduction

      6.2 Procedures for determination of arrester specification

      6.3 Determination of test values for arrester protective levels and wave shapes for

            coordinating currents

            6.3.1 Arrester protective levels

            6.3.2 Amplitude of coordinating current

      6.4 Current sharing between parallel resistor columns

      6.5 Arrester energy stresses

7 ARRESTER TESTING

      7.1 General principles

            7.1.1 Protective characteristics

            7.1.2 Energy withstand capability

            7.1.3 Verification of thermal stability

            7.1.4 How to consider results from pollution tests

            7.1.5 Pressure relief test

            7.1.6 Insulation withstand test

            7.1.7 Importance of current sharing requirements

            7.1.8 Selection of test samples

      7.2 Type tests

            7.2.1 Residual voltage test

            7.2.2 Operating duty test

                  7.2.2.1 Energy withstand test and high current test

                  7.2.2.2 Accelerated ageing procedure

                  7.2.2.3 Verification of thermal stability

7.2.2.4 Verification of thermally prorated section

      7.3 Routine tests