| Due to the nonlinear loads,line faults,and the coupling of AC and DC lines,etc.,it is difficult to avoid the presence of DC components and harmonic components in power systems.In the AC environment with DC components,there is a deviation in the measurement of conventional electromagnetic current transformers,which will cause incalculable damage to the power grid.In contrast,the anti-DC current transformers have better metering characteristics.However,for the verification of anti-DC current transformers,there is no effective anti-DC current transformer verification system because of the lack of relevant verification standards.Therefore,it is of great practical significance to carry out research on the verification of anti-DC current transformers.This paper proposes a new verification method and conducts in-depth discussions and studies for the verification of anti-DC current transformers.Firstly,the secondary current waveform and spectrum of conventional electromagnetic current transformer and anti-DC current transformer under sinusoidal half-wave current are analyzed in the papaer,and the transmission characteristics of anti-DC current transformer is obtained.Secondly,the paper compares and analyzes the principle and characteristics of the current transformer verification method,and proposes a digital direct verification technical solution.In order to solve the problem of saturation and misalignment of conventional standard electromagnetic current transformers in half-wave currents,high-accuracy shunts are used as standard current channels,which can test the error of the anti-DC current transformer at the half-wave current and full-wave current.In addition,based on the analysis of the existing algorithms,this paper presents a high-precision multi-spectrum-line interpolation fast Fourier analysis algorithm,and detailedly deduces the principle of the algorithm and the correction of the fitting process.In the complex verification environment,this algorithm can effectively suppress the problem of spectrum leakage under non-synchronous sampling and has higher accuracy in the extraction of fundamental and harmonic waves.The detailed design scheme of the system is given in the paper.The system’s host computer software is designed,and a prototype of an anti-DC current transformer verification system is developed.The paper carries out error analysis of the verification system and conducts a comparative experiment against anti-DC current transformer and conventional electromagnetic current transformer.The analysis and experimental results show that the anti-DC current transformer verification system designed in this paper achieves the precision class up to 0.1 and has good operability,practicality and human-computer interaction. |
