Working principle of protective current transformer

The protective current transformer is generally used for the relay protection circuit of multiple busbars. It is developed for the protection system to detect short-circuit faults. It has different accuracy levels and accuracy limit coefficients, can be expanded to different perforation sizes, and is widely used in low-voltage distribution protection systems. It can also be used to collect low-voltage overload and short-circuit signals and is used in conjunction with protection relays.

Product advantages

Novel structure, beautiful appearance, easy installation, small size, light weight, high accuracy and large capacity.

Structural features

The shell is made of flame-retardant, temperature-resistant 140°C imported polycarbonate injection molding, the core is made of oriented cold-rolled silicon steel strip, and the secondary wire is made of high-strength electromagnetic enameled wire.

The working principle of the current transformer is shown in Figure 1. The primary winding of the current transformer is connected in series in the measured line. I1 is the line current, that is, the primary current of the current transformer, N1 is the primary number of turns of the current transformer, I2 is the secondary current of the current transformer (usually 5A, 1A), N2 is the secondary number of turns of the current transformer, and Z2e is the impedance of the secondary circuit equipment and connecting wires. When the primary current flows in from the P1 terminal of the current transformer and out from the P2 terminal, when the secondary Z2e is connected, the current I2 flows from S1 through the secondary winding of the current transformer, through Z2e to S2, forming a closed loop due to the principle of electromagnetic induction. It can be obtained that the current is I1×N1=I2×N2 in an ideal state, so I1/I2=N2/N1=K, where K is the transformation ratio of the current transformer.