3) Figure 3 is the number comparison of lightning trip
outs happened on 500kV AC transmission lines and ±
500kV DC transmission lines during the year 2010 to
2012. The former accounts for 74.7%, while the latter
only 25.3%. Two reasons contribute to the discrepancy:
One is the larger amount of AC transmission lines; and
another is most towers in DC transmission lines adopt
negative protection angle, which has higher shielding
properties. In addition, positive correlation of ground
flash density and lightning trip outs can be seen by
comprehensive analysis of Figure 1 and Figure 3.