Analysis And Optimization Of Electromagnetic Immunity Of Electronic Current Transformer Acquisition Card

With the development and promotion of smart grids,electronic current transformers have been increasingly used.Practically,the electronic current transformers are arranged near the high-voltage equipment or even on the cabinet.Thus,the operating status of the high-voltage equipment can be monitored in real time,which improves the intelligence level of the power grid.However,due to the complex electromagnetic environment of the power grid,the electronic equipment arranged therein will suffer severe electromagnetic interference.Erroneous alarming and malfunctions occur,and even,the electronic equipment will undergo non-recoverable damage.That is a great threaten to the security of the power grid and restricts the construction of smart power grid.This paper focuses on the acquisition card of electronic current transformers,and analyzes the interference induced by the switching on and off of the power grid on the acquisition card.In this paper,damped oscillatory wave is utilized to simulate the transient process of the switching operation of power grid.A large number of tests of actual damped oscillatory wave interference are conducted on the acquisition card.Combined with computer simulation tools,models of the acquisition card and damped oscillatory wave generator are established in computer software,and the waveforms of the key points of the acquisition card under the interference of the damped oscillatory wave are simulated.Finally,according to the general solutions for suppressing electromagnetic interference,two ways are proposed to improve the performance of electromagnetic immunity of the acquisition card in the electronic current transformer.On the one hand,the performance of the operational amplifier in the main integration circuit of the acquisition card is analyzed,and the failure mechanism of the operational amplifier under the interference of the damped oscillatory wave is investigated.Besides,the coupling mechanism of damped oscillatory wave in the acquisition card is derived through analyzing the field coupling of the printed circuit board.A high-voltage low-pass filter is proposed to remove the interference noise superimposed on the normal signal.The electromagnetic immunity level of the acquisition card is improved,and the failure of the electronic current transformer during the on and off operation of the grid switch is reduced.On the other hand,the design of the power supply of the acquisition card is optimized.By inserting a shielding winding in the Fly-back transformer,the propagation path of the common mode noise in the Fly-back converter is changed.Via the quantitative design of the shielding winding,the common mode noise of the Flyback converter in the output side can be suppressed.Therefore,the quality of the chip supplier is improved,which is conducive to the maintaining the function of the chip.