Transient identification of lightning strokes on ±800 kV UHVDC transmission lines

When thunderbolt directly strikes on UHVDC transmission line and does not lead to line fault, the voltage traveling wave on polar line alternately fluctuates around the DC component and the correlation degree between the voltage traveling-wave and the direct voltage line is close to 1. Such a feature can be used as the criterion to identify lightning disturbance. When lightning fault occurs, there are lots of high-frequency components in lightning wave, which attenuates quickly after the insulation is broke down; when earth fault occurs, the traveling wave of short-circuit voltage is caused by additional power supply, so there are few high-frequency components in it. The lightning stroke fault finally takes on the feature of earth fault, and after the wavelet transform the medium- and low-frequency components due to lightning stroke are similar to those of earth fault, thus the ratio of high-frequency components caused by lightning stroke to medium- and low-frequency components is larger than that of earth fault, accordingly such a feature can be used to distinguish lightning stroke fault from earth fault. Utilizing the model of ±800 kV UHVDC power transmission project from Yunnan to Guangdong and adopting the time window with the width of 5 ms, a lot of EMTP simulation are performed, and simulation results show that the proposed method is effective.