Abstract
At present, great attention is paid to the problem of improving the accuracy of measurement information received in the electrical networks. The highest error is observed in currents obtained using instrumental electromagnetic current transformers (CT). It takes place due to CT saturation core during transient states including fault in the primary, costumer commutations and magnetizing–current inrush. The saturation process can start in the first cycle or in the following cycles of transient state.
The article represents literature analysis of increasing data reliability received from CT during both transient state and steady-state mode. The techniques based on usage of distorted secondary current, CT core magnetization curve and magnetic flux according to start of saturation process in the CT magnetic system. The sophistication of existing methods was revealed and their advantages and disadvantages are showed.
In the beginning of the paper, the systematization of existing methods was performed on the basis of classical and modern methods. Classical methods are characterized using optimization of core absolute permeability. Modern techniques of secondary current compensation make use of the mathematic modeling using curve magnetization and prediction of the transient values of the distorted signal. Further, testing results of more effective existing techniques and their comparison analysis are performed. During testing, the accuracy of secondary current compensation is determined with sampling rate according to IEC 61 850 standard i.e. 80 samples per cycle of commercial frequency (4 kHz). In conclusion, the appropriateness of making use of the described techniques was proved and future work in this direction was proposed.
Keywords
Current transformer (CT), secondary current, CT core saturation, magnetizing current, magnetization curve.
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