Study And Design Of Electronic Current Transformer Used To Measurement Small Current

Current transformer is an important equipment in power system. And it plays a primary role for working well and calculating precisely in power system. With the development of national economy, all kinds of new voltage levels and current levels emerge continuously, the high precise of measurement and protection are demanded increasingly. As a result, the electronic current transformers will certainly substitute the old electromagnetic ones for its predominant speciality. The electronic current transformer is based on modern electronic technology and optical technology, it has been widely used in power engineering because of its high precision, high stability, wide response bandwidth and strong anti-jamming. In order to measure small current (In the world the current which is less than 1000 A is called small current) accurately, this paper designed a high precise electronic current transformer. This transformer adopted Rogowski coil as sensor. Because the mutual inductance of Rogowski coil is very small, the induced voltage is so feeble that it is very difficult to measure the small current accurately. So this paper adopted the new materials to make the high precise and mutual inductance Rogowski coil with new method. Besides this paper designed a new disposal system to deal with the induced voltage. In this disposal system the paper adopted one circuit to accomplish measuring and protective function at the same time. The system included the circuits of preamplifier, controllable amplifier, integrator, low pass filter and phase– modulator. Because this paper adopted high precise components to compose circuits, the precision of signal disposal system and the electronic current transformer can be increased greatly. According to the experimental data, it can be seen that the current transformer this paper designed could work reliably. At the range of -40~70 oC, it can work steadily. Furthermore the ratio error and phase error of current transformer could satisfy the state criterion of 0.2 standard. Relative to the tradition electromagnetic current transformers the respond speed and bandwidth are increased greatly. As a result, it is hopeful that the electronic current transducer we designed is practical.