The Energy Juggler: Power System Inertia Keeping the Lights On!

The electricity grid is a complex and incredibly important system, and one of the most impressive engineering feats of the modern era. Today, the US power grid is the world’s largest machine, containing more than 7,300 electricity-generating plants.

Understanding the importance of mainting the grid frequency stable is a must to further understand how this beatiful and massive machine is evolving from its inception.

Put in simple words, all the devices and appliances we use in our daily life are designed to be safe at Power Frequencies (50-60Hz). Once the frequencies move out of this range, especially for extended periods (even a few seconds), this results in previously safe systems no longer being safe. This damage is even clearer at a power system generation level:

• The current in motors and transformers changes with frequency. So, if the frequency drops suddenly, it can overload the system with too much current, which can be really damaging.
• If the frequency spikes unexpectedly, it can lead to insulation failures. This can cause massive electrical short circuits, and the consequences can be disastrous.
• The damage caused by these problems can be extremely expensive. Taxpayers might end up spending hundreds of millions of dollars in both the short and long term. Equipment might fail prematurely, before it's supposed to, and that's a big financial burden.

For a long time, power system inertia has been the life jacket that helped the grid to overcome this types of events.

The National Renewable Energy Laboratory (NREL) defines Inertia in power systems as to "the energy stored in large rotating generators and some industrial motors, which gives them the tendency to remain rotating."

This stored energy acts like a backup power source, stepping in temporarily when a generator fails. It's like having a secret superhero ready to save the day! This quick response, usually lasting just a few seconds, gives the mechanical systems in power plants some breathing room. They can detect the problem and react in time to handle the failure. - Thanks Inertia for saving us! ?

But then, why are we worrying now about maintaining frequency stable? Well, our superhero is just losing its power. Inertia comes from synchronus generators, basically the conventional fossil, nuclear, and hydropower generators. But as the power grid evolves, things are changing. More and more renewable energy sources like wind, solar panels, and batteries are joining the party. The thing is, these new sources don't naturally provide Inertia.

So what will happen now? Will we have blackouts every couple hours? Will our refrigerators, TVs, washing machines, ect start breaking up?

A new superhero has arrived in town! - Fast Frequency Response (FFR)

FFR is all about how certain resources, like generators and load response, can step up and supply energy super quickly. These resources, which use inverters instead of mechanical parts, are speed demons when it comes to increasing energy supply. Why is this important? Well, as the grid's inertia decreases, the frequency can drop faster. But don't worry! FFR comes to the rescue by responding rapidly and helping to balance out the frequency decline.

I won't enter into much more detail here about multiple potential sources of FFR, as it becomes a more technical reading. But I completely recommend this NREL technical report for the ones of you who want to dig more into this fascinating topic.