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The increasing use of natural gas power generation has strengthened the interdependence between the power and natural gas subsystems in the integrated power and gas system (IPGS). Due to the interactions between the two subsystems, the disturbances in one system may spread to the other one, triggering a disruptive avalanche of subsequent failures in the IPGS. This paper presents a survey of cascading failure analysis for the IPGS. First, we identify the important features characterizing cascading dynamics in individual power and gas subsystems. Then, we will discuss the features for the cascading failure analysis in the IPGS and future research. 

The growing penetration of renewable resources such as wind and solar into the electric power grid through power electronic inverters is challenging grid protection. Due to the advanced inverter control algorithms, the inverter-based resources present fault responses different from conventional generators, which can fundamentally affect the way that the power grid is protected. This paper studied solar inverter dynamics focused on negative-sequence quantities during the restoration period following a grid disturbance by using a real-time digital simulator. It was found that solar inverters can act as negative-sequence sources to inject negative-sequence currents into the grid during the restoration period. The negative-sequence current can be affected by different operating conditions such as the number of inverters in service, grid strength, and grid fault types. Such negative-sequence responses can adversely impact the performance of protection schemes based on negative-sequence components and potentially cause relay maloperations during the grid restoration period, thus making system protection less secure and reliable.