61869-2

Representing the percentage error at rated current.

Understanding the IEC 61869-2 Standard for Current Transformers 61869-2

Classes include 0.1, 0.2, 0.2S, 0.5, 0.5S, 1, 3, and 5 . Representing the percentage error at rated current

Here’s the rub: A VT can be a perfect 0.2 class for metering at nominal voltage, but a terrible 3P for protection at 5% voltage (near a fault). 61869-2 mandates both tests. I've seen procurement specs that only mention "Class 0.2" and forget to specify the protection class, resulting in a VT that bills accurately but blinds the distance relay during a close-in fault. Don't do this. The standard is clear: if it's used for both, specify (e.g., "0.2 / 3P"). 61869-2 mandates both tests

In short, IEC 61869-2 isn't a page-turner. But if you want your voltage measurements to survive a nearby lightning strike, a harmonic storm from a solar farm, and a digital relay's relentless sampling—this is the document that makes it possible. Respect the VT. Read the standard.