Intentional Controlled Islanding and Risk Assessment: A Unified Framework

Abstract

Abstract--Power systems are prone to cascading outages leading to large-area blackouts, and intentional controlled islanding (ICI) can mitigate these catastrophic events by splitting the system into sustainable islands. ICI schemes are used as the last resort to prevent cascading events; thus, it is critical to evaluate the corresponding system risks to ensure their correct operation. This paper proposes a unified framework to assess the risk of ICI schemes. First, a novel ICI method to create islands with minimum power imbalance is presented. Further, a risk assessment methodology is used to assess the probability and impact of the main operational modes of the ICI scheme. The unified framework provides insights on the benefits of implementing ICI, considering the uncertainties related to its reliability. The ICI scheme is demonstrated using the IEEE 9-bus system. The proposed unified framework is then fully deployed on the actual power system of Cyprus. Multiple case studies on the real network are created to demonstrate the adaptability and robustness of the proposed scheme to different system conditions. The adoption of the unified framework highlights that the system risk significantly reduces with the ICI in service, even when the reliability uncertainties associated with the scheme are considered.

Active splitting strategy searching approach based on MISOCP with consideration of power island stability

“…Thus, it is necessary to make a trade-off between the requirement of handling the stability issues and the requirement of real-time decision. It is commonly agreed that the sudden active power imbalance is the primary and the severest threat to the island transient stability after system splitting [18,[20][21][22]27]. A large power imbalance disturbance caused by the splitting action would possibly lead to insufferable frequency dip/rise on the islands, and severely threaten the island transient process.…”

“…Constraint (22) depicts the inevitable load loss considering the island inertia and the governor regulation capability during the frequency dynamics. As illustrated in (22), the rational division of the load nodes will greatly impact the frequency dynamics, which also indicates the necessity of considering the frequency response capability. Since SSS is generally controlled in a sufficiently short time, the generator mechanical power at the decision-start time is used to approximate P mec d ðt 0þ Þ with a reasonable assumption that the mechanical power of each generator does not considerably change during the SSS process.…”

“…Compared with the transient disturbance restriction in [18], the power imbalance restriction in (22) reflects the island frequency response capability rather than an empirical threshold. Meanwhile, because the transient frequency process is modeled as linear constraints, it does not introduce considerable computational burden for SSS.…”

“…3. The TEC in (22) represents the lower limit of temporary load shedding and does not lead to a break in feasibility. Consequently, the model (23) always has a feasible solution.…”

“…However, the threshold for the island active power disturbance is empirically determined and fails to take the island regulation ability into account, which may lead to a conservative or aggressive result. Similarly, several studies consider TEC by addressing the island active power disturbance problem caused by the system splitting, such as minimizing the pre-split island power flow exchange [21], minimizing the post-split island power imbalance [22], and so on.…”