Why protective relays are the watchdogs of electrical power systems

By Hector Medina | July 31, 2018

If you were living near the Great Lakes in the US or Canada in 2003, you probably have a very distinct memory of Thursday, August 14. That was the day…and night…and part of the next day…when 55 million people were left without electricity.

At first, most of my friends and family took the event in stride, even saw it as an opportunity to have outdoor gatherings and socialize in the natural lights of the night sky—something virtually impossible to do when the city lights are running. For most, the novelty wore off quickly. Just a couple of days without refrigerators, televisions, and air conditioning (an August necessity in this region) was enough to make people realize how important it is to have reliable power systems.

So, what went wrong? Actually, it was a series of small events that cascaded into larger issues and eventually forced power grids and generating stations to disconnect from each other. For those who aren’t familiar with electric distribution systems, it comes down to one basic rule: an electric grid is stable as long as the provided electricity matches the required load. In other words, electricity producers must match their output to the grid’s demands. If demand exceeds supply, the grid can become overloaded—as happened in the 2003 blackout—as it attempts to pick up the extra load. If this happens, the limitation is in both power production and the size of the electric lines themselves. As a line becomes overloaded, it heats up, the conductive metal expands and the line then sags down into unwanted territory (like a tree, for example) and can cause a fault.

Electrical protective relays are devices that protect our power systems from damage. They detect when a power source or power line is close to becoming overloaded and promptly disconnect it. Doing so avoids costly damage and, more importantly, reduces the electrical hazards in order to protect people

These devices were already in place during the 2003 blackout. Yet, we still suffered a catastrophic event that cost two countries billions of dollars. Obviously, something still needed to be improved. So organizations like the North American Electric Reliability Corporation (NERC) started planning to upgrade our electric power systems to mitigate the likelihood of similar events reoccurring.

Working together with regional reliability councils such as the Northeast Power Coordinating Council (NPCC) and the Independent Electricity System Operator (IESO), NERC developed a new set of directives and standards that required electricity producers and distributors to make changes to their systems in order to improve communication and reliability.

The new NERC rules cover many parts of the electrical grid system, including electrical protective relays. It’s not just about compliance, but rather competitiveness. Updating these relays can have significant financial benefits. Where single-function relays were once the name of the game, upgrades in the technology and software in past decades now allow for multifunction relays. Less equipment means less risk and lower maintenance costs; more dollars added to our clients’ bottom lines.

It’s important to understand how compliant a site already is before starting to make changes. Sometimes, the surrounding/indirect work required to make a site compliant is more significant than the relay replacements themselves. For example, having to replace cabling infrastructure is often a more costly and cumbersome task compared to replacing equipment. Companies should understand this and address it as part of their risk management plan. Ignorance is not bliss. Unforeseen modifications can add significant costs and result in delays later down the line.

Software and the internet have changed the industry since protective relays were first installed in our power plants and transmission systems. Nowadays, the software is so critical to performance that it is qualified to the highest degree. Protective relays have evolved from electromechanical pieces of equipment into digital intelligent electronic devices (IEDs). Thus, software qualifications and cyber-security are of utmost importance. When selecting vendors or manufacturers, one should verify that they are reputable, can offer all the necessary documentation, and practice the highest degree of rigor and care. 

The work to update our power systems (complete with protective relays) and bring them into compliance is one of the power industry’s most pressing challenges. It’s work that can be costly and laborious, but it also offers opportunities to leverage new technologies and go beyond standards to find ways to make systems smarter and more efficient. All of which ultimately still saves money.

It’s the kind of work we engineers love doing. Tackling the tough problems to find smarter solutions to some of our industry’s biggest challenges. Especially when you know that you’re working on projects that could have such a wide-ranging impact, and could keep the lights on for yourself and millions of others.