Study on fault mechanism of LCC-HVDC large disturbances under cloud-to-ground lightning with long continuous current

The safe and stable operation of the line commutated converter high voltage direct current (LCC-HVDC) system is of great significance to the reliability of electricity supply. In order to clearly reveal the mechanism of LCC-HVDC large disturbance fault under the Cloud-to-Ground (C-G) lightning with long continuous current, the HVDC-lightning simulation model considering long continuous current, actual control and protection systems is proposed. The effect of long continuous current on traveling wave protection is analyzed. Transient processes including commutation failure (CF), fault restart and blocking of the DC system under the lighting with long continuous current are simulated. The reasons for CF of LCC-HVDC system caused by long continuous current are analyzed, and the influence of long continuous current amplitude and duration on fault restart process is studied. Results show that the long continuous current has little influence on the response characteristics of travelling wave protection, but during the regulation process of control system under lightning disturbance, the DC current control regulation quantity will increase due to the presence of long continuous current. If the amplitude of long continuous current exceeds 80 A, the CF will occur in the DC system. If the duration of long continuous current exceeds the deionization time, the line will fail to restart, and the line can be successfully restarted only if the long continuous current is over before the voltage begins to rise.