SF6 density relays with protection and control functions are widely used in AC/DC transmission systems.Due to the differences in the principle of fault cutoff in AC/DC transmission systems,the risk of abnormal operation of SF6 density relays is significantly higher in DC transmission systems than in AC transmission systems.Therefore,risk assessment must be conducted for live gas replenishment,gas measurement,and other operations on their gas circuits.The risks caused by abnormal operation of SF6 density relay at the moment of connection with external gas circuit are ana-lyzed,and experimental verification is conducted.Suggestions for improving the SF6 pressure low blocking protection cri-terion of SF6 insulation equipment in DC transmission systems have been proposed for industry reference.
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