Field frequency data of three real event cases from SMD-Ls.

Case 1:  a fast event.

At 17:21:31 on March 18, 2020, the second-line circuit breaker in Shanan, Jibei, China tripped. The valid SMD-L data points in the AC network of North China are in place H, Z, X, and N. 

Case 2:  a slow event.