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TB 086 1994 SC 33 /21/14 JWG 33/21/14.16 Overvoltages on HVDC cables.

The number of HVDC projects using long DC cables is increasing, mostly for submarine power transmission. A larger number of such HVDC schemes are already in operation or in planning stage. The economic design of DC cables is very important, because the cost of DC cables is high in proportion to the total cost of HVDC submarine cable transmission.

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TABLE OF CONTENTS

1 INTRODUCTION AND SCOPE OF JWG 33/21/14-16

2 DATA OF HVDC CABLES

3 PRESENT PRACTICES FOR TESTS OF HVDC CABLE 

4 INSULATION CAPABILITY

      4.1 Electric Stresses in the Insulation

      4.2 Overvoltages and Cable Design

5 OVERVOLTAGES

      5.1 Internal Overvoltages

            5.1.1 Overvoltages lower than 1.5 p.u.

                  5.1.1.1 Normal Power Changes

                  5.1.1.2 External Disturbances Causing Voltage Variations

                  5.1.1.3 DC Side Disturbances

            5.1.2 Overvoltages Higher than 1.5 p.u.

                  5.1.2.1 Loss of Firing Pulses in inverters or inverter Blocking

                  5.1.2.2 Start against Open End

                  5.1.2.3 Fault on OC in Mixed Overhead Line/Cable Trans­mission

      5.2 External Overvoltages

6 MEANS FOR REDUCTION OF OVERVOLTAGES

      6.1 Gapless Metal Oxide Arresters

      6.2 Arrester with Parallel Gap

      6.3 Thyristor Controlled Arrester

      6.4 Arrester in Series with Diode

      6.5 OC Damping Circuit

7 WITHSTAND CHARACTERISTICS OF HVDC CABLES

8 INSULATION COORDINATION

      8.1 General

      8.2 Recommended Minimum Margins between Protective and Withstand Levels

            8.2.1 Lightning Overvoltages

            8.2.2 Internal Overvoltages

            8.2.3 Long Duration AC Type Overvoltages

9 CONCLUSIONS

10 REFERENCES