How to correctly install the zero-sequence current transformer?

1. Preparation before installation
1. Check the appearance of the transformer:
Check whether the appearance of the zero-sequence current transformer is damaged, cracked or deformed, and ensure that its appearance is intact.
Check the nameplate information of the transformer to confirm whether its model, specification, rated current, accuracy level and other parameters meet the design requirements.
2. Confirm the installation environment:
Ensure that the ambient temperature, humidity, altitude, etc. of the installation site meet the use requirements of the transformer. Generally, the ambient temperature is required to be between -25℃ and +70℃, the relative humidity does not exceed 90%, and the altitude does not exceed 2000 meters.
The installation site should be free of corrosive gases, flammable and explosive gases, and conductive dust to avoid strong magnetic field interference.
3. Check the primary circuit:
Confirm that the wire cross-sectional area, material and laying method of the primary circuit meet the design requirements, and the wire connection is firm without looseness or virtual connection.
Ensure that the phase line and neutral line (N line) of the primary circuit pass through the zero-sequence current transformer.
2. Precautions during installation
1. Installation location selection:
The installation location should be convenient for inspection and maintenance, and avoid installation in humid, high temperature, dusty or corrosive gas places.
Try to install it in the distribution box or switch cabinet, and avoid installing it outdoors or in open places to reduce the impact of environmental factors on the transformer.
2. Installation method:
Fix the transformer at the installation location to ensure that it is firmly and stably installed to avoid loosening or damage to the transformer due to vibration or external force.
The installation direction of the transformer should be correct to ensure that the flow direction of the primary current is consistent with the polarity mark of the transformer.
3. Primary wire passing through the transformer:
Ensure that the three-phase wire and the neutral wire (N wire) pass through the transformer, and the wires should be kept parallel to avoid entanglement.
When the wire passes through the transformer, ensure that the insulation layer of the wire is intact to avoid contact between the wire and the transformer core.
4. Secondary wiring:
The secondary wiring should be firm and reliable to avoid looseness or poor contact. The secondary wiring should use a copper core wire with a cross-sectional area of ​​not less than 1.5 square millimeters.
The output end of the secondary winding should be connected to the residual current protection device or measuring instrument to ensure correct connection and avoid wrong connection or missing connection.
The secondary circuit should have good grounding measures, and the grounding resistance should meet the design requirements, generally not more than 4 ohms.
5. Avoid secondary open circuit:
During the installation process, it is strictly forbidden to open the secondary side of the transformer, otherwise it may cause high voltage on the secondary side, endangering the safety of personnel and equipment.
If the secondary circuit needs to be inspected or tested, the primary circuit should be powered off first to ensure safety.
6. Grounding protection:
Ensure that the grounding terminal of the transformer is reliably grounded, and the grounding wire should use a copper core wire with a cross-sectional area of ​​not less than 2.5 square millimeters.
The grounding wire should be directly connected to the grounding busbar or grounding electrode to avoid indirect grounding through other equipment or conductors.
III. Inspection and debugging after installation
1. Appearance inspection:
After the installation is completed, check the appearance of the transformer again to ensure that it is firmly installed without looseness or damage.
Check whether the secondary wiring is firm and whether the wiring terminals are loose or not.
2. Insulation test:
Use a megohmmeter to perform insulation test on the secondary winding of the transformer to ensure that its insulation resistance meets the requirements, generally not less than 10 megohms.
During the test, the two ends of the secondary winding should be short-circuited, and then its insulation resistance to ground should be measured.
3. Polarity check:
Use a multimeter or polarity tester to check the polarity of the transformer to ensure that the flow direction of the primary current is consistent with the polarity mark of the transformer.
If the polarity is reversed, the measurement result will be inaccurate and may even affect the normal operation of the protection device.
4. Load test:
When the primary circuit is energized, load test the transformer to check whether its output signal is normal.
During the test, a standard current source or actual load can be used to observe whether the output current of the transformer is proportional to the primary current.
5. Protection device debugging:
Connect the output end of the transformer to the residual current protection device or measuring instrument to debug the protection device.
During debugging, the operating current and operating time of the protection device should be set according to the design requirements to ensure that it can operate reliably in the event of a fault.
6. Record installation information:
After installation, the installation location, model, specification, wiring method and other information of the transformer should be recorded in detail for future maintenance and repair.