Unveiling the Secrets: A Basic Guide to Current Transformer Construction

Here’s a concise overview of the basic construction of a current transformer (CT): 

Purpose: An instrument transformer known as a current transformer is structured to induce an alternating current in its secondary winding. The magnitude of this alternating current is directly linked to the current being assessed in its primary winding. 

• Primary Winding: The primary winding consists of only one or very few turns. It can be a single flat turn, a coil of heavy-duty wire wrapped around the core, or a conductor (bus bar) passing through a central hole. 
• Secondary Winding: The secondary winding has a large number of coil turns wound on a laminated core of low-loss magnetic material. This core has a large cross-sectional area to maintain low magnetic flux density.

• Core: The core is the magnetic material that links the primary and secondary windings. It can be made of iron, steel, ferrite, or other materials. The core provides a low reluctance path for the magnetic flux generated by the primary current.
• Insulation: The insulation is the material that separates the primary and secondary windings and prevents electrical contact or short circuit. It can be paper, plastic, epoxy, or other materials. The insulation also protects the windings from moisture, dust, and corrosion.
• Terminal block: The terminal block is the device that connects the secondary winding to the external circuit. It can be a screw, a clamp, a plug, or other types of connectors. The terminal block provides a secure and convenient connection for the output current.

 

Operation: The primary winding is in series with the current-carrying conductor supplying a load. The secondary winding provides a current into an ammeter or resistive load. 

Types: 

Wound Current Transformer: Primary winding physically connected in series with the measured current. Secondary current depends on the turns ratio. 

Toroidal Current Transformer: No primary winding; the line carrying current threads through a window in the toroidal transformer. 

Bar Current Transformer: Similar to toroidal, but with a bar-shaped core.