"Functions and Core Structure of Toroidal Current Transformers"

As a specific type of current transformer (CT), the toroidal CT functions by converting a high primary current into a proportionally lower secondary current based on a specific transformation ratio. This is primarily used for protective relaying and electrical measurement. Since instruments cannot be directly connected to conductors or busbars carrying extremely high currents, a CT is required to step down the current to a manageable secondary value, which can then be scaled back up using the transformation ratio to reflect the actual primary current.

The operating principle and equivalent circuit of a toroidal CT are identical to those of a standard transformer. The key difference is that its primary winding has very few turns and is connected in series with the measured circuit. Meanwhile, the secondary winding is connected to low-impedance loads, such as ammeters or relay current coils, effectively operating in a near-short-circuit condition. Both the primary and secondary currents are determined solely by the load on the measured line and are independent of the secondary load on the CT itself.

Of particular note is the toroidal core of this CT. It is manufactured from premium cold-rolled grain-oriented silicon steel, renowned for its low iron loss and high magnetic permeability. Available thicknesses include 0.05 mm, 0.08 mm, 0.1 mm, 0.2 mm, 0.23 mm, 0.27 mm, 0.3 mm, and 0.35 mm. Due to its continuous closed-loop magnetic path structure, it exhibits zero leakage flux and superior magnetic performance. Additionally, this design allows for rapid and convenient winding using toroidal winding machines, resulting in high production efficiency.