Estimation of the WECC System Inertia Using Observed Frequency   Transients
  Computer models being developed to understand the interaction between demand-response technology, power system deregulation and market transformation depend in part on understanding the relationship between system frequency and load-control. Frequency, load, and plant outage events data collected over the last several years have permitted analysis to determine the Western Electricity Coordination Council (WECC) system's inertia during each event. This data was used to evaluate the relationship of system inertia to total load, which is used to model system response to load curtailment programs in next generation power system simulations. 
David P. Chassin, Zhenyu Huang, Matthew K. Donnelly, Candee Hassler,   Enrique Ramirez, Cody Ray