A merging unit (the device that samples the CT's analog signal and converts it to a digital Ethernet stream) expects a perfect analog input. If the CT's phase error is 1 degree at 10% burden, the merging unit will digitize that error, and the protection relay will calculate the wrong impedance. A fault 10 km away will appear to be 9.8 km away. The zone-1 protection might not trip.
Sarah navigated to the technical specifications on her tablet, pulling up the digital twin of the device based on the IEC standard. "According to 61869-2, for a TPY class in this fault current, the transient factor should handle 80% offset. But the test shows the core is saturating way earlier." iec 61869 2
The adoption of IEC 61869-2 provides several benefits, including: A merging unit (the device that samples the
Let us go to a factory in Shenyang, where a TPX class CT is being type-tested. A test engineer, call her Mei, applies a 20 kA primary current with a 70% DC offset—a "worst-case" per 61869-2. The zone-1 protection might not trip
It covers equipment with rated frequencies from 15 Hz to 100 Hz .
"You make the standard sound like a hero," Sarah joked.
Some of the key requirements of IEC 61869-2 include: