Inertia in One Lesson (Dave Edwards on LinkedIn)

By Robert Bradley Jr. -- May 6, 2025

“The challenge with rising renewables: As power systems rely more on asynchronous generation, frequency changes can occur much faster, increasing the risk of grid instability.” (- Dave Edwards_

Dave Edwards post begins: “As an engineer I like to understand how systems operate, this is useful for fault diagnosis, especially when a system fails and a Root Cause is needed, though maybe more than one contributing factor. So let’s Talk “Inertia” 🙋‍♂️Everyone’s Saying It, But Who Really Understands It 🤷‍♂️”

The floor is his:

“Inertia” is getting a lot of airtime in power system discussions lately, but what is it, really, and why is it so critical for grid stability on an electrical power generation system.

More importantly, which generation technologies actually provide useful inertia⁉️

Image created using Chapt GPT 4o

❓What is inertia?

Think of inertia a bit like us seasoned engineers on LinkedIn: “It’s the ability of an object (engineer) to resist change.”

For rotating objects (like generator rotors), this is called rotational inertia or moment of inertia.

👉 Two key factors influence it:

• Mass
• Mass distribution (i.e., the object’s shape)

Example: A solid disk and a ring with the same mass and radius have different moments of inertia.

• Solid disk: Mass is closer to the center = lower inertia

• Ring: Mass is farther from the axis = higher inertia, result, the ring is harder to start or stop spinning.

👉 Why does this matter in power systems? The spinning parts of generators store kinetic energy, which helps stabilise grid frequency during sudden events, like a generator or interconnector tripping offline.

👉 What actually provides useful inertia? Synchronous generators (coal, gas, hydro, nuclear):

• Spin in sync with grid frequency (e.g UK: 50Hz, US: 60Hz)
• Have large rotating masses, provide physical inertia.
• Help slow down frequency changes, giving time for systems to react, either demand or generation.

Asynchronous generation (most wind turbines, all solar PV):

• Magnetically decoupled from grid.
• Has little or no rotating mass.
• Provide minimal to no physical inertia.

💡The challenge with rising renewables: As power systems rely more on asynchronous generation, frequency changes can occur much faster, increasing the risk of grid instability.

To counter this, we need –

• 🔋 Fast battery response
• ⚙️ Synthetic inertia
• 🧠 Grid-forming inverters
• ⚡️ Synchronous Compensators

or just plain old conventional generation like nuclear or gas.

👉 Bottom line:

As we increase renewable penetration, understanding and managing inertia becomes critical.

It’s not just a buzzword, it’s foundational to keeping the lights on 💡

Hopefully if you didn’t know, you now know what inertia is in the context of the grid and why important for grid stability.