What precautions should be taken when wiring current transformers?

1. The secondary side must never be open-circuited.
The secondary side of a current transformer must never be open-circuited during operation. If the secondary side is open-circuited, it will cause a sharp increase in the core magnetic flux, generating high voltage (up to several thousand volts), which may damage equipment or endanger personal safety. Switches or fuses are prohibited in the secondary circuit.
2. Reliable grounding
One end of the secondary side must be reliably grounded (usually the K2 terminal). Grounding prevents high voltage from the primary side from entering the secondary side in case of insulation breakdown between the primary and secondary windings. However, it should be noted that there should only be one grounding point to avoid multiple grounding points causing malfunction of protective devices or inaccurate measurements.
3. Correct polarity connection
The polarity must be correct when wiring. In my country, current transformers use the subtractive polarity marking method, where the primary side L1 and the secondary side K1 are corresponding terminals. Incorrect polarity will lead to malfunction of protective devices or damage to instruments.
4. Primary side wiring direction
The primary side current should enter from the P1 terminal and flow out from the P2 terminal (P1 connected to the power source side, P2 connected to the load side). Reverse wiring (P2 in, P1 out) will lead to inaccurate metering.
5. Secondary load impedance limit
The secondary load impedance should not exceed the allowable value to ensure that the current transformer operates within the required accuracy class. If the secondary circuit needs to be switched, measures to prevent open-circuiting must be taken.
6. Common wiring methods
Select the appropriate wiring method according to system requirements, such as single-phase wiring, two-phase V-connection, three-phase star connection, etc. For example:
Two-phase V-connection: Suitable for ungrounded neutral systems, it can measure three-phase current and protect against phase-to-phase short circuits.
Three-phase star connection: Suitable for three-phase four-wire systems, it can protect against any type of fault.
7. Other precautions
The secondary windings should be connected to separate circuits such as measuring instruments and protective devices.
Ensure that the wiring is secure during installation to avoid poor contact leading to open circuits.
Regularly check the insulation status of the secondary circuit to prevent insulation aging from causing accidents.