Manufacturing Process of Current Transformer
Manufacturing Process of Current Transformer
Inspect the toroidal core for excitation characteristics, dimensions, winding tightness, and ensure no burrs, sharp edges, or rust on the surface. Wrap multiple layers of crepe paper and semi-conductive insulating tape around the outer layer of the core to isolate it from the secondary winding.
Use a current transformer toroidal winding machine to wind enamel wire onto the core. Place polyester film insulation paper between layers to ensure interlayer insulation. After winding, lead out the secondary leads through high-temperature sleeves to enhance insulation and secure the wire ends. Apply semi-conductive insulating tape and polyester ribbon over the outer side of the secondary winding to form an overall insulating buffer layer, which helps distribute the electric field evenly and reduce partial discharge.
Bend copper busbars into primary coils, insert them through the central hole of the core for positioning, and weld the primary terminal connections.
After winding, test the coil for DC resistance, insulation resistance, volt-ampere characteristics, and turns ratio. Reject non-conforming products for rework; pass products proceed to the next process.
Place the coil in an oven for preheating and drying to remove moisture, preventing bubble formation and excessive partial discharge during resin curing inside the coil.
Preheat and premix epoxy resin, hardener, and silica micro-powder separately. Deeply mix the two-component epoxy resin and hardener independently under vacuum to degas thoroughly. Mix fully via a static mixing system, degas again, and strictly control material temperature to prevent premature gelation.
Install the APG mold onto the equipment, clean it thoroughly, and close the mold. Heat the mold to the required process temperature (120–130°C, adjusted according to the epoxy formulation). Spray release agent into the mold, allow it to evaporate briefly (1–3 minutes), then place the transformer coil into the mold and secure it. Re-close and lock the mold tightly. Connect the injection port and begin high-pressure injection of epoxy resin, using continuous pressure to compensate for shrinkage during curing. Maintain pressure for 20–40 minutes after filling to allow rapid gelation and curing at constant temperature. Release pressure by opening the vent valve, open the mold, and remove the product. Trim off the injection ports, flash, and burrs, and finish the exterior appearance. Inspect the surface for cracks, voids, defects, or other flaws.
Place the product into an oven and cure at a controlled temperature for 3–6 hours according to the process curve, ensuring complete resin curing and improving mechanical strength and insulation performance.
Conduct tests on finished units including DC resistance measurement, turns ratio, polarity, error, demagnetization, phase difference, insulation resistance, power frequency withstand voltage, partial discharge, no-load current, volt-ampere characteristics, and dimensional inspection. Reject non-conforming products; approve qualified ones for storage.
Install baseplate, junction box, and terminal blocks. Print nameplates, clean, package, and store the products.
