Study on modeling and simulation of AC/DC sensitive residual current transformer

AC/DC sensitive residual current transformer (AC/DC RCT) is used to detect residual sinusoidal alternating currents, residual pulsating direct currents or residual smooth direct currents and the characteristics of AC/DC RCT is of great signification for residual current protection under complicated waveform conditions. An AC/DC RCT based on magnetic modulation principle is proposed. Modeling and simulation of the AC/DC RCT is studied. Firstly, the B-H curve of permalloy magnetic core is fitted accurately by using a mixed method of expressions and the least squares method (LSM), which can overcome the shortage of low accuracy of the traditional charting or piecewise approximation methods. Secondly, based on the analysis of operation principle of AC/DC RCT, the loop equation of AC/DC RCT is obtained and a computer based simulation model is established. Thirdly, on the basis of the simulation model, the effects of secondary winding turns on oscillation frequency of AC/DC RCT is studied when the material and geometric dimension of the magnetic core is defined. And the simulation results of output voltage under residual sinusoidal alternating currents or residual smooth direct currents conditions are given. Finally, the feasibility of the simulation model is verified by experiment. The research results are helpful for the design of AC/DC RCT.