How Many Phase Angle Systems Are Used in The Protection and Control World?
This should be an easy question…
A-Phase is shown on this phasor diagram at 0 degrees. What angle would be used to describe B-Phase?
Click here to see the correct answer
There are three possible correct answers
- 120°
- -120°
- 240°
The actual correct answer will depend on the equipment you are using.
Here’s another question about the same phasor diagram. What Phase rotation is depicted in that phasor diagram? If your drawings do have a phase rotation diagram, it might look like the one below.
Click here to see the correct answer
The correct answer for this phase rotation is either:
- A-B-C
- B-C-A, or
- C-A-B
They all describe the same phase rotation with different references.
If you weren’t sure about either question, or the answer surprised you; then you may be:
- “testing” your IEDs/relays,
- getting passes on your test sheets, and
- then putting them into service where they will NEVER operate.
Modern IEDs look at the sequence components to figure out what kind of fault is on the power system so that it applies the correct formulas to the correct fault…AND they also use that information to figure out where the fault is.
If the IED/relay is connected to a power system with the wrong phase rotation, or is connected to look in the wrong direction; nothing it measures on the power system will make sense and it may disable itself to prevent mis-operations.
If you don’t understand the phase rotation symbols on your drawings or the phase angle system your test equipment and IED/relay uses; then you may be applying the values you need to get those checkmarks on your test report, but the IED/relay will never operate because your test angles don’t match the power system angles the IED/relay will be connected to.
I recorded these videos to help you figure out what phase angle system your IED/relays and test equipment uses and how to tell the phase rotation of a power system. They are based on a paper I presented at the NETA PowerTest conference in 2022. I hope you find them useful.
Introduction to Phasor Angle Descriptions
What Are Phasors and How to Determine Phase Rotation
The Most Common Phase Angle Systems (Lagging, Cartesian/Official/Leading, and Combined)
Applying Phase Angle Systems to IED/Relay Testing…and the Negative Lagging Angle System
If you want to truly understand how to apply the concepts in these videos and become a true IED/relay testing craftsperson, click here to learn about our online IED/relay testing training programs.
Not sure if our training is right for you, sign up to our technical newsletter to get more free high-voltage electrical testing tips:
Discover more from Valence Electrical Training Services
Subscribe to get the latest posts sent to your email.
Did you like this post?
You can share it with these links:
