1.When using a current transformer (CT), in addition to meeting requirements for primary current and rated voltage, the CT must also satisfy requirements for dynamic and thermal stability under short-circuit conditions.
2. The secondary circuit of an operating current transformer must never be left open. If the secondary circuit is open, the demagnetizing effect of the secondary current is lost, causing the entire primary current to act as magnetizing current; this leads to a sharp increase in magnetic flux density in the core, resulting in overheating and potential burnout of the transformer. Furthermore, core saturation generates high voltage on the secondary side, endangering personnel and equipment safety.
3. To prevent hazards to personnel and equipment in the event of insulation breakdown between the primary and secondary windings, the secondary side of the transformer must have a reliable ground connection.
4. Ensure correct polarity when wiring the current transformer.
5. The accuracy class of the current transformer should be at least one grade higher than that of the connected instruments. Class 0.5 CTs are generally used for standard electric energy metering; however, Class 0.2 CTs should be used for metering applications involving generators, main transformers, and large industrial consumers where higher measurement accuracy is required.
6. Select an appropriate rated capacity for the current transformer; the actual load of the secondary circuit must fall within the transformer's rated load and minimum load limits to ensure the specified accuracy class is maintained.
7. To ensure safety, measuring instruments should not share the same secondary winding with protective relays.
8. Current transformers used for protection purposes must possess a sufficiently high "10% error limit factor" (often referred to as the "10% multiple").
Note: The "10% error limit factor" (or "10% multiple") of a current transformer refers to the multiple *n* of the rated primary current at which the current error reaches -10%. A higher factor indicates superior overcurrent performance for the transformer.