Protective relays are on a hair trigger as they constantly look at the three-phase electric power system and try to decide whether the system is normal, or under fault conditions. If they detect a fault, they will attempt to isolate that fault from the rest of the electrical system.
Electro-mechanical relays use magnets and mechanisms to look for specific problems on the three-phase power system, and each relay model should have identical functions and wiring. This allows relay testers to follow a script that creates the specific criteria required to make the mechanisms move, and prove that that specific function is operating correctly. Relay testers do not need to understand the three-phase power system when testing this generation of relays because the relays are identical and perform simple functions.
Modern digital relays can be extremely complex with interactions between elements and endless logic configurations. This means that two identical relay models can have completely different functions. While it is possible to carry the electro-mechanical testing philosophy into the digital realm by re-programming the relay when testing each element, this style of testing will not prove that the relay will operate when required. A relay tester who understands the three-phase electrical system can build test plans that test the entire relay, instead of individual pieces of it, to make sure the relay operates when required. These procedures can also be more effective and efficient than traditional test procedures.
We will cover the following topics in this lesson to give you a foundation in three-phase electrical theory to help you become a better relay tester:
Introduction to Electrical Fundamentals and Frequency
- How electricity is created
- What is a cycle
- How to count cycles
- Understand how frequency and cycles are related
- Converting cycles to seconds
- Converting seconds to cycles
- Converting cycles to cycles
Three-Phase Electric Power Systems
- How three-phase electric power systems are created
- How to determine what kind of three-phase electric power system is being generated
- How to change one kind of three-phase electric power into another
You might see this list and think that you already have a firm grasp on these topics. Test your knowledge with this quick quiz:
What You Need to Take the Course
Most of the course content uses a Video streaming video service, which is the equivalent of YouTube (without the ads, of course). You need a good internet connection, a computing device that can stream video, and some privacy (or headphones) to watch the videos. You can make all videos full screen by clicking the “Enter Full Screen Icon” 
on the bottom right hand side of the controls.
Course Tips and Tricks
This course was originally created using Adobe Flash technology, which was the premier method for course creation not that long ago. Flash has fell out of favor since then and will soon cease to be a supported platform.
We have converted the course material to videos, which means that we lost some of the interactivity (this as the reason we chose Flash in the first place). We strongly encourage you to keep your hands near the Video controls so you can pause and rewind the videos to better understand the information. None of the controls on the video itself will work and we’ve tried our best to make that clear in the videos.
We could possibly add speed controls (to speed up or slow down the videos while they are playing). If enough people ask for this option by emailing store@relaytraining.com, we may add this feature in the future.
You can ask questions about any topic in the comment section, or ask unrelated questions in the course forums. We read and respond to every comment we see!