How to Size TP-Class CTs (TPX, TPY, TPZ) | IEEE vs IEC Method Explained

🔹 Why asymmetrical short-circuit current (with DC offset) pushes CTs into deep saturation
🔹 The IEEE C37.110 method — and why it works only for single-energization
🔹 Why the IEEE approach is not valid for auto-reclosing or double-energization duty cycles
🔹 The IEC 61869 method for transient-performance CTs
🔹 What Kssc and Ktd mean — and how they define the CT core
🔹 How Ktd changes with relay operating time (real example: 40 drops to 21)
🔹 How digital relays (fast tripping) reduce CT oversizing
🔹 A simple walkthrough of the Ktd Sizing Tool based on the IEC VBA script

This video is not just about formulas — it is about understanding what is happening inside a TP-class CT during DC-offset faults, and how to size the CT so it stays accurate when it matters most.

Whether you work in transmission, distribution, industrial systems, or GIS environments, this is essential knowledge for reliable protection engineering.

📌 Watch the earlier video: Asymmetrical CT Saturation — highly recommended before watching this one
   • Asymmetrical CT saturation | DC-Offset | E...  

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