What are the best practices for applying load shedding schemes to prevent cascading failures?

1 What is load shedding?

Load shedding is the deliberate reduction of electric load by disconnecting some customers or areas from the power supply. It is usually done as a last resort when the power system is facing an emergency situation, such as a generation shortfall, a transmission line fault, or a frequency drop. Load shedding aims to balance the supply and demand of electricity, and to prevent the system from collapsing due to overload or instability.

2 Why is load shedding necessary?

Load shedding is necessary to protect the power system from cascading failures, which can have disastrous consequences for the society and the economy. Cascading failures can be triggered by various factors, such as natural disasters, cyberattacks, human errors, or equipment failures. They can propagate quickly and unpredictably across the grid, affecting millions of customers and critical infrastructures. Load shedding can help to isolate the affected areas, reduce the stress on the remaining system, and restore the normal operation as soon as possible.

3 How to design load shedding schemes?

When designing load shedding schemes, it is essential to consider the particular characteristics and needs of the power system. This includes criteria and thresholds for initiating load shedding, such as frequency, voltage, power flow, or contingency analysis. Additionally, the amount and location of load to be shed should be based on the priority, sensitivity, and impact of different customers and regions. Furthermore, the coordination and communication between different entities must be taken into account. Automation and speed of load shedding actions can be achieved with devices such as underfrequency relays, under-voltage relays, or synchrophasors. Lastly, recovery and restoration plans must be made after load shedding, including the reconnection sequence, the load restoration rate, and the frequency and voltage regulation.

4 What are the challenges of load shedding?

Load shedding is not a perfect solution and comes with several challenges and limitations, such as the uncertainty and variability of the power system conditions, the trade-off between reliability and efficiency, and the social and ethical implications. Additionally, there are technical and regulatory barriers that can hinder coordination between stakeholders and jurisdictions. These issues can affect the cost and quality of service for customers and providers, as well as raise issues of fairness, transparency, and accountability.