Power System Protection Basics

Power system protection refers to the methods and technologies used to detect and isolate faults in an electrical power system, preventing damage and ensuring the reliable operation of the grid.

Increased deployment of inverter-based resources such as wind, solar photovoltaics, and battery energy storage has raised questions about how to protect the power grid if there is a fault, or abnormally high or low electrical current, which can happen for a variety of reasons.

Fault Protection and Why It Matters

The most typical type of grid fault is a short circuit. On the power grid, short circuits can occur, for example, when two wires touch, or when a tree touches a wire. This causes the generators to produce a big surge of electrical current, also known as fault current. The surge can lead to fires and damage to equipment, if not corrected.

Fault current can also be helpful, though, because it alerts the grid that something isn't right. Circuit breakers on the grid detect abnormally high levels of current and quickly disconnect that part of the grid, which prevents damage.

Maintaining Fault Protection on the Evolving Power Grid

In today's power system, fault current is mostly produced by synchronous generators in fossil, nuclear, and hydroelectric plants that can inherently and automatically produce large amounts of current. Many of these traditional generators are being replaced with inverter-based resources, which are not typically designed to produce large amounts of fault current like traditional synchronous generators.

There are multiple options to maintain fault protection with high levels of inverter-based renewables that are already being used in locations throughout the United States. One option is to deploy inverter-based resources that have the ability to provide more fault current (requiring oversizing certain components in the inverter). Another option is to rely on synchronous generators. These include renewable resources that use synchronous generators (such as concentrating solar power, biomass, or geothermal), and deploying stand-alone devices installed to provide fault current.

Additional Resources

Power Grid Protection Research

Strengthening Our Grid Against Tomorrow’s Threats, NREL Fact Sheet (2022)

Inertia on the Power Grid, NREL Fact Sheet (2020)

Inertia on the Power Grid, NREL Technical Report (2020)