Study on EMS of DC SSR under interference of EFT burst

EFT (electrical fast transient) burst generated when electromechanical component is breaking or closing often disturb the secondary electrical equipment which directly coupled to power supply and grounding, and indirectly couple to signal cable by inductance and capacitance. In this paper, the EMS (electromagnetic sensitivity) of a DC SSR (solid state relay) in which transformer isolation circuit was adopted was investigated. Firstly, the equivalent circuit model of EFT burst generator, which was prescribed in GB/T 17626.4-1998, was proposed by calculating parameters of components of charge-discharge loop in complex frequency domain. Then, considering of the high frequency model of dual-winding transformer, the accurate equivalent circuit model of DC SSR for EMS analyzing was built. Finally, the circuit model of EFT burst generator and DC SSR were combined with each other in Orcad Pspice software to simulate the EMS of SSR under different test levels of EFT. The simulation results agreed well with the experimets and the validation of the analysis method proposed in the paper was proved.