Upgrading electromechanical protection relays to modern digital relays? Read this!

Posted on February 27, 2023 written by Josée Bergeron

Since the early 1900s electromagnetic relays have been a mainstay of electrical power transmission and distribution systems around the world. Other than a short stint when solid state (static) relays were developed in the 1960s and 1970s, electromagnetic relays have been the most used protection relay in the 20th century. However, protection relays have come a long way since American scientist Joseph Henry invented the electromagnetic relay in 1835 especially since the advent of the microprocessor based (digital) relays in the 1990s. As old electromechanical, solid state (static) and even first generation protection relays are needing upgrades, industries are opting for the advantages of modern digital relays. 

Advantages of digital relays

Upgrading to modern digital relays makes a lot of sense. Modern digital relays offer significant advantages over electromechanical, solid state (static) and even first generation protection relays. Here are some solid reasons for upgrading to modern digital relays.

Improved reliability

Digital relays don’t have moving parts so they aren’t prone to failure because of wear and tear, dirt and dust, and vibrations. You know that time someone slammed the breaker door and tripped the electromechanical relay causing an outage - that doesn’t happen with digital relays. Ultimately, the increased reliability of digital relays will pay for itself. 

Greater adaptability

Digital relays can handle complex systems and be programmed to provide protection functions for a range of power system components. They can also be adjusted as needed, even remotely. For example, the overcurrent curve shape can be changed on the fly in a digital relay whereas with an electromechanical relay you’re stuck with what you’ve got. This advantage can help solve miscoordination challenges. 

Communication capabilities

Digital relays can collect data, provide metering, diagnose problems, report events and communicate with other relays, devices, and control systems, which gives you accurate data for faster and more efficient decision-making and fault detection. The current, voltage and power metering is especially helpful since this wasn’t available at all in the electromechanical relays without additional transducers.

Safety of employees

Because digital relays allow for more complex settings, this will frequently result in reduced arc flash hazards compared to electromechanical relays. Arc flash is a big deal these days, sometimes this improvement alone is enough to justify a relay upgrade project.

Reduced maintenance cost

Digital relays don’t have moving parts and so there is less need for periodic testing and calibration, which is time-consuming and expensive. On top of the reduced maintenance cost, digitals relays stay more accurate throughout their lifespan.

Things to consider before upgrading to digital relays

The advantages of upgrading to digital relays seems like a no-brainer, but before jumping in and modernizing your relays there’s a few things to consider. By being prepared and hiring experts you can avoid costly surprises along the way and ensure a successful project.

Questions to ask

Before jumping in to upgrading your electromechanical relays to digitals relays here are some questions to consider:

  • Do we have up-to-date wiring documentation? Are our wires well labelled?
  • Are there regulatory or utility requirements that we must meet?
  • In the case where the relays are mounted in switchgear, should we upgrade the relays or should we replace the entire switchgear line up?
  • In the case of replacement of several relays with a single digital relay, how can we be sure we’re selecting the right type of relay?
  • Which relay brand and part number should we select? There are a lot of factors playing into this decision and it pays to get it right.

Hiring an expert

It pays dividends to hire electrical engineers with high levels of experience when it comes to upgrading your protection relays. They’ll know what questions to ask, offer innovative solutions to your unique upgrade and provide efficient and on budget service. If you’re looking for an expert to help our team at Delta Wye have years of experience with this type of project and would be happy to help. 

Also, if you’re convinced you need to upgrade your electromechanical relays, but your manager is sitting on the fence. Use this article to build a business case to convince your boss! Also, feel free to reach out to us for more information.


Lundqvist , Bertril, (n.d.) “100 years of relay protection, the Swedish ABB relay history” ABB Automation Products, Substation Automation Division https://library.e.abb.com/public/c1256d32004634bac1256e19006fd705/PAPER_2001_08_en_100_Years_of_Relay_Protection__the_Swedish_ABB_Relay_History.pdf

Ransom, D. L. "Upgrading relay protection? — Be prepared," 49th IEEE/IAS Industrial & Commercial Power Systems Technical Conference, Stone Mountain, GA, USA, 2013, pp. 1-8, doi: 10.1109/ICPS.2013.6547351. 

Woodford, C. (2021, December 2). “Relays. Explain That Stuff.” https://www.explainthatstuff.com/howrelayswork.html