How to properly install and use a current transformer?

1. Pre-installation Preparation
Power-off Operation: Before installation, disconnect the power supply. Wear insulating gloves and safety glasses. Check the transformer's appearance and specifications to ensure it matches the circuit requirements.
2. Tools and Materials: Use copper wire (cross-section ≥ 2.5 mm²) for the secondary circuit conductor. Clearly number both ends to avoid confusion.
3. Installation Position and Direction
4. Direction Marking:
Current transformers are marked with P1 (power side) and P2 (load side). During installation, ensure that the current flows from P1 to P2.
For through-hole transformers, pay attention to the wiring direction, with P1 facing the power side (for example, for the live wire of phase A, P1 should face upward).
5. Location Selection:
Near the starting or ending point of the circuit, away from strongly magnetic objects (such as iron).
In three-phase systems, the sampling transformer is typically installed on the phase A conductor (such as in reactive power compensation scenarios). III. Wiring Specifications
1. Primary Wiring:
The live wire enters the transformer from the P1 side and exits from the P2 side, ensuring correct polarity.
2. Secondary Wiring:
Connect S1 to the positive terminal of the meter, S2 to the negative terminal, and reliably ground them (to prevent open-circuit high voltage).
Three-phase meters must be wired according to phase sequence (e.g., yellow, green, and red correspond to the transformer S1 terminal).
3. Grounding Requirements:
All S2 terminals must be short-circuited and grounded at a single point to avoid errors caused by multiple grounding points.
IV. Commissioning and Testing
1. Pre-Power-On Inspection:
Confirm that all connectors are securely fastened, insulation intact, and the ground wire is securely connected.
2. Testing Method:
Apply power gradually to the low-voltage side and use a multimeter to measure the secondary output current to ensure it matches the transformation ratio (e.g., a 100/5A transformer should output 5A). V. Common Issues and Precautions
Open circuits on the secondary side are strictly prohibited: Open circuits can result in dangerous high voltage. Ensure S2 is grounded and the circuit is intact.
Transformation Ratio Matching: The meter and transformer ratio must match (e.g., a 100/5 transformer paired with a 200/5 meter requires adjustment).
Three-Phase System Differences:
Three-phase balanced loads (such as motors) can be measured with a single transformer, while three-phase, four-wire systems require three transformers (including the neutral current).
Metering transformers must be calibrated by the power supply department (0.5S accuracy).
VI. Special Scenarios
Zero-Sequence Transformer: Pass the cable ground wire through the center hole of the transformer to ensure that the ground current is detected.
Reactive Power Compensation: The sampling transformer should be located close to the power supply to reflect the load current of the entire plant.