Mini Current Transformer: Production Process

Miniature current transformers (CTs) play an important role in the electrical devices for measurement or protection, such as electricity meters, smart grid, and other electrical instruments. As a professional manufacturer with more than 15 years experience, we introduce the production process of a typical current transformer as below. Of course, different kinds of current transformer may vary a little during the process.

Magnetic Core Inspection

The journey of a current transformer start from a core made by soft magnetic material. There are a variety of magnetic cores suited for different types of CT. For example, DC immune current transformers need Fe-based amorphous & nanocrystalline composite cores, zero phase current transformers may need silicon steel cores or Fe-based nanocrystalline cores. Each piece of the core should be tested before coil winding and make sure the induction value within limit.

Coil Winding

When we get the qualified cores, we’ll wind the coils by automatic winding machines. We choose different size of jigs according to the enamel wire length and gauge. Every winding coil should be inspected before further processing. Extra material and labor will be wasted, if we do not remove the defect coils from the production lines.

Coil Assembly

Usually, the enamel wires, which used to pass the secondary current, are not strong enough. So, we should solder them to lead wires with PVC sleeves or connect pins in PCB mount current transformers. After soldering, the process varies according to the current transformers’ encapsulation methods. We can put the coil inside a plastic case with liquid epoxy resin filled later; or wrap the coil by insulation tapes and heat-shrink sleeves. The busbar, or primary wire may be assembled at the same time.

Inspection and Packing

For each piece of CT, we should test the current error and phase tolerance (or phase shift). The test result should meet the National Standard or the customers’ requirements. In China, the required current error and phase tolerance for different accuracy class of miniature current transformer is stipulated by GB/T 10665. Usually, current transformers of accuracy 0.1 class is good enough for most applications, although our high precision current transformers can achieve accuracy class of 0.05 or 0.02, with a little higher price.

After inspection, qualified products will be packed by small paper boxes inside and cartons outside. For some occasions, we’ll use plywood case or pallet to protect these cartons from damaging during long transshipment.