Metrological and Transient Analysis of Combined Instrument Transformer Coupled with FEM-3D Magnetic Field Study

In the paper a 20 kV combined current-voltage instrument transformer (CCVIT) metrological and transient characteristics will be calculated by using numerical methods. The CCVIT is a non-linear electromagnetic system consisting of two magnetic measurement cores (voltage VT and current CT measurement core) with mutual magnetic influence and two electrical winding systems which increase the voltage, current and phase displacement errors. The non-linear iterative calculation of the magnetic field distribution in the three-dimensional domain is achieved by using the finite element method and an original and universal program package FEM-3D. The initial design of CCVIT is made according to the analytical transformer theory. The FEM-3D results are basis for the further genetic algorithm (GA) optimal design. The objective function in the optimization process is the minimum of the CCVIT steady state metrological parameters. The optimization GA coupled with FEM-3D methodology given in the paper derive positive design results from metrological aspect. After steady state metrological analysis is done, transient CCVIT characteristics are derived by coupling with the FEM-3D magnetic field study.