How to handle excessive secondary load on current transformers?
Sep 12, 2025| I. Emergency Measures
1. Load Transfer
Immediately deactivate non-essential instruments (such as redundant metering devices) and prioritize ensuring the operation of the protection circuit.
Switch the overloaded CT to the backup circuit via a switching operation (the backup CT capacity must be verified).
2. Temporary Load Reduction
Reduce the primary current to 80% of the rated value (requires dispatch coordination).
Short-term overload operation is permitted (no more than 1.2 times the rated current), but enhanced monitoring is required.
II. Technical Optimization Solutions
1. Impedance Matching
Connect two sets of CTs with the same secondary parameters in series (total load impedance is halved).
Replace low-impedance cables (e.g., 4mm² copper cable instead of 2.5mm²).
2. Equipment Upgrade
Replace high-capacity CTs (e.g., 0.2S-class instead of 0.5-class).
Use 1A secondary current CTs (loss reduced by 25 times).
III. Long-term Preventative Measures
1. Design Verification
According to DL/T Calculate secondary loads according to 866-2015 standard (including cable length correction).
Differential protection circuits must ensure the impedance error of the CTs on both sides is ≤0.5%.
2. Operation and Maintenance Management
Test secondary circuit impedance (volt-ampere method) quarterly.
Install CT secondary overvoltage protectors (operating voltage ≤150V).
