# Review of Power System Resilience Concept, Assessment, and Enhancement Measures
## 5 Enhancement Measures for Power System Resilience
### Measures after an Event  
Traditional recovery strategies may not be able to cope with severe natural disasters because, after the disaster, the major equipment and interdependent infrastructure may be damaged [10, 54]. Resilient systems, when dealing with disruptions, are designed to \"bend\" instead of \"break\", meaning they must possess flexibility and survivability. For instance, utilizing emergency power sources to provide temporary support or reconfiguring system  
Figure 7: Comparison of two systems with the same load loss under different circumstances. (**a**) A system lacking capabilities of absorption and recovery. (**b**) A system with better capabilities of absorption and recovery. configurations will enhance a system's flexibility [11]. To maximize the load capacity of the power system and minimize the duration of power outages, various hardening and operational measures are implemented to enhance the power system's resilience. Based on the optimized resilience metrics, enhancing system resilience means slowing down the rate of system performance degradation, which involves improving the capabilities of resistance, withstanding, and absorption of the system. This can be realized through the implementation of hardening measures, such as grid hardening. On the other hand, improving the capabilities of adaptation and recovery of the system to reduce the duration of such a state can also enhance the system's resilience. This can be achieved through operational measures, such as distributed energy resources (DER), microgrids, and advanced smart grid technologies. * Grid hardening  
Increasing the strength of infrastructure enhances its durability and stability, making it more capable of withstanding the impacts of extreme events and reducing damage [60]. For example, overhead power lines are the most vulnerable components in a distribution system, as they are susceptible to damage from external factors such as weather, vegetation, animals, and human interference. Recommended measures include upgrading utility poles and towers with stronger materials can make them more robust and durable, and replacing overhead power lines or other transmission and distribution lines with underground cables can effectively reduce damage caused by external factors [57; 80]. However, underground cables are challenging to locate in cases of faults and repair, and the cost of burying the entire electrical network underground is high. Therefore, a compromise solution is to identify the critical components in the system and prioritize their underground installation. It is crucial to consider the potential impact of extreme events and improve construction standards accordingly before constructing new distribution systems [81]. Additionally, relocating facilities to areas less prone to flooding or elevating substations can protect the electrical system from flood damage [15]. * Distributed energy resources  
Even with the implementation of emergency response plans and disaster preparedness plans before and during extreme events, it is not possible to completely avoid power outages [13]. The availability of generator sets is crucial to ensure power supply to critical loads during extreme events [2]. Distributed energy resources such as distributed generators (DG), micro-turbines (MT), fuel cells (FC), mobile power sources (MPS), and renewable energy sources (RES) can generate, store, and control power locally, enabling more efficient response to emergencies and reducing the occurrence of power outages caused by events [10; 57]. Additionally, energy storage can balance the supply and demand of power during disruptions. Integrating distributed energy resources and energy storage into the distribution network and rerouting resources can improve the availability of power generation. Therefore, accurately determining their location and size greatly contributes to enhancing power system resilience [82; 83; 84].