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The fault conditions at the receiving end of the hybrid cascaded UHVDC project cause the transmission energy to be blocked, and the sending end cannot respond quickly in a short time, resulting in temporary excess power in the receiving system. A DC controllable self-recovery energy dissipation device for a hybrid cascaded UHVDC project is proposed. The related technical research is carried out, the working principle of the controllable self-recovery energy dissipation device is explained, and the design scheme of the controllable self-recovery energy dissipation device is given. Finally, the feasibility and reliability of the controllable self-recovery energy dissipation device for suppressing system transient overvoltage are verified by simulation. The successful development of the controlled self-recovery energy dissipation device provides a new technology for suppressing transient overvoltage of hybrid cascaded UHVDC faults. more...

For suppress the amplitude of overvoltage from HVDC sending terminal, an overvoltage suppression scheme based on the principle of controllable energy dissipation was proposed. The overvoltage mechanism of a weak AC system under the fault of the DC system was analyzed, and the method and operating principle of the CSREDD were proposed. Prototype of the develop CSREDD was tested, which proved correctness about the design. The controllable energy dissipation device has been successfully applied to the ±800kV Lu-Gu UHVDC transmission project. The operation results show that the controllable energy dissipation device can effectively suppress the AC overvoltage. more...

The MMC converter valve adopts the water-cooled heat dissipation method. The automatic exhaust valve is installed at the upper part of the main water pipe, and the manual ball valve is installed between the automatic exhaust valve and the main water pipe, which is made of insulating material. During laboratory tests, it was found that the switch state of the manual ball valve may lead to an abnormal discharge of the manual ball valve. When the manual ball valve is closed, it is filled with air, and the insulating material bears high voltage, and the air inside will be broken down. This paper studies the abnormal discharge phenomenon of the manual ball valve, analyses the discharging principle, evaluates the influence on converter valve equipment, and proposes an optimal design scheme. more...