Study On The Reliability Of The Electronic Current Transformer Based On The Rogowski Coil

Transformer is the key equipment that draws current or voltage in power system. With the increase of the voltage grade and the transmission capacitance in power system, the traditional electromagnetic current transformer has presented some shortcomings, such as magnetic saturation,dangerous caused by the secondary side open and insulation problem et al.. Due to its excellent performance in magnetic saturation and in insulation, the electronic current transformer has attracted great attention of researchers and has been preliminarily applied in State Grid. In application, however, the action of the sensing head of the electronic current transformer is easily affected by the surrounding factors such as atmosphere temperature and electromagnetic interference, leading to poor measurement accuracy and poor stability of its continuous operation. The accuracy and reliability of the measurement of electrical parameters in power system is an important guarantee for the safe, reliable and economic operation of power system. Hence, although the electronic current transformer is considered to be an ideal substitute of the traditional one, it is still necessary to do further investigation and improvement for the electronic current transformers.In this thesis, the development status of the electronic current transformer has been introduced systematically. In addition, the composition, operation principle, and problems left open for the electronic current transformers based on Rogowski coils have been expounded. Focused on the reliable measurement of the electronic current transformer, the performance and optimization design of Rogowski coils have been investigated.The sensing principle of Rogowski coils with rectangular cross section is analyzed, and an improved analytical model of estimating the relative error of the coil output voltage caused by thermal expansion has been derived, which is relative to both the thermal expansivity of the coil materials and the coil structure parameters. The errors estimated by using the improved model are in better agreement with the experiments than those by using the reported model.To reduce the influence of thermal expansion on the coil measurement accuracy, taking into account the working environment of Rogowski coils and the requirement for measurement accuracy for the coil, the cera mics with lower thermal expansivity and the enameled copper wire are chosen to the coil skeleton and coil winding, respectively, and the corresponding error analysis has been done, showing an error estimation below 0.0432%, which satisfies 0.2S accuracy standard for the electronic current transformers.The effects caused by the electromagnetic interference when taking into account the thermal expansion have been analyzed. Two analytical expressions of estimating the relative error of the coil output voltage caused by horizontal and vertical components of the interference magnetic field have been given, the influences of atmosphere temperature and the distance from the origin current producing interference magnetic field have been calculated and analyzed, and further, the measures of resisting the electromagnetic interference such as electromagnetic compensation and electromagnetic shielding, etc are proposed. The above studies provide guidance for high accuracy Rogowski coil design.