Transformer for DC current magnitude conversion. The utility model utilizes the nonlinearity and asymmetry of the iron core in the core coil to be magnetized by the direct current and the alternating current, and converts the direct current of the direct current passing through the coil into a direct current with a small direct current by a rectification circuit through a rectifying circuit. It is mainly used to measure DC high current and is also used as current feedback, control and protection components in rectifier systems. Compared with the shunt (see ammeter), it has low power loss and isolation. The lines of commonly used DC current transformers are shown in the figure. In the figure, A and B are two identical but independent cores. The DC large current I1 flows through the two primary windings (ie, the feedthrough wires in the figure, which is equivalent to the primary N1=1匝), and the secondary windings on both cores are N2匝, which are connected in reverse polarity and are sinusoidal. Power supply. As the polarity of the supply voltage alternates, the two cores will be in deep saturated and unsaturated state in turn. Under ideal conditions, the difference between the voltage of the supply voltage U and the load resistor Rx is borne by the secondary winding on the unsaturated core, and there is N1I1=N2I2 or I1/I2=N2/N1 (I2 is the secondary current), ie I2 and I2 are inversely related to the number of turns. After rectification, I2 can be read by a DC current meter or calculated by the voltage drop across the load resistor Rx.
After the 1930s, the accuracy of the DC current transformer was increased to 0.1 due to the use of additional compensation windings. With the development of electronic devices, the even-order harmonic components in the core flux are amplified and fed back to form an automatically compensated zero-flux DC transformer with an error of less than 0.01%.