Current transformer core is one of the important equipment in the power system, which can accurately and effectively transmit and transform the electrical information on the high-voltage side of the power grid.The normal operation of the current transformer is of great significance to the transient protection equipment, electric energy metering equipment and operation monitoring equipment in the power system.
When the power system runs normally and stably, no residual magnetism will be generated in the Current transformer core.However, due to the hysteresis property of magnetic materials in Current transformer core, when a short circuit fault occurs, the short circuit Current will form a large amount of residual magnetism in the core.Current transformer core remanence will improve its normal working flux level, leading to its core saturation phenomenon, causing secondary Current distortion, reducing the accuracy level of power metering and the reliability of relay protection action.
The principle of current transformer is based on the principle of electromagnetic induction.The ct is composed of a closed core and winding.The number of turns of its primary winding is very small and is strung in the line of the current to be measured.
Therefore, it often has all the current of the line flowing through. The number of turns of the secondary winding is relatively large and is connected in series.
In the measuring instrument and protection loop, when the ct is working, its secondary loop is always closed. Therefore, the impedance of the series coil of the star-measuring instrument and protection loop is very small, and the working state of the ct is close to short circuit.
The function of current transformers is to convert the primary current with a large value into a secondary current with a small value through a certain ratio, for protection, measurement and other purposes.A current transformer with a transformer ratio of 400/5 can convert an actual current of 400A into a current of 5A.
Current transformer core has laminated square core and round core.The former has the advantages of easy winding and installation of coils, while the disadvantages are air gap, poor magnetic properties, large magnetic leakage of coils and more trouble in lamination.The advantage of the latter is no air gap structure, good magnetic properties, the disadvantage is difficult to wind the coil.