By comparison with busbar type current transformer (CT), the structure of toroidal current transformer is simple. Usually, there is a through-hole of no less than 8mm diameter, which allows the primary wire or copper busbar come through. The through-hole may be “I” type or “+” (cross) type, which can fix the busbar properly and make it’s very easy to assemble the current transformer.
Construction of Toroidal Current Transformer
- lead wires
- heat-shrink sleeve
- outcase
- soft magnetic core with winding coil
The illustration above shows the basic parts of a mini current transformer before filling the epoxy resin. The heat-shrink sleeve prevent the lead wires from damaging, which is not always required for very tiny current transformers. The outcase may be plastic PBT or metal shield, which make the dielectric voltage no less than 3000 V. Sometimes, the outcases can be replaced by insulation tape, which is convenient for small lot production as not plastic mold should be developed in advance. We usually place nanocrystalline cores or DC immune dual cores inside, as they have high initial premeability and high saturation flux density. For zero phase current transformers, silicon steel cores can be adopted, due to the cost advantage.
After placing these parts together, we should pouring epoxy resin in the outcase and inspect the phase error and other parameters before shipment. The whole process of production is introduced as below post.