Q: Why do we care about a few hundred milliohms (mΩ) in the CT winding?
A: Because internal resistance is part of the Total Burden. It limits how much voltage the CT can produce before it saturates.
The Logic:
• CT must produce voltage: Es = Is × (Rct + Rburden).
• High Rct (loose contact/damage) → CT works harder → Saturates early.
• Result: Protection Relay fails to see fault current correctly.
How to measure the Secondary Winding Resistance of CT.
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Secondary Winding Resistance test range 0~300Ω; accuracy: 0.2%±2mΩ