Study On Leakage Current Protection Technology Under Nonlinear Loads

With the rapid development of smart grid and power electronics technology,nonlinear loads are widely used.When electrical faults happen,the resulted leakage current is no longer sinusoidal AC,but is pulsating DC or smooth DC,or even complex leakage current including high frequency components.As a result,the traditional leakage current protection device can not meet the new requirements.Based on the analysis of the conventional leakage current protection technology,a series of new technologies have been studied to solve the problems with nonlinear loads.Firstly,the influence of pulsating DC residual current(leakage current)on the operation performance of type AC residual current protection device(RCD)has been investigated.And reasons why traditional type AC RCDs refuse to trip under complicated residual current also have been revealed.Both analyses can provide foundations for the further research.Secondly,the traditional AC and DC residual current measurement methods are analyzed separately,including electromagnetic induction method and dual-core magnetic modulation method.On this basis,a single-core magnetic modulation residual current measurement method is introduced.Moreover,the corresponding residual current protection method is proposed.Thirdly,a new single-core magnetic modulation based on RCD has been designed.According to the actual operation condition of nonlinear loads,a wide-range magnetic modulation residual current transformer is designed to ensure the effective transformation of measured residual current.In addition,the power circuit,the signal conditioning circuit and the controller circuit are implemented,and the software design are carried out as well.Finally,several tests have been conducted for the new RCD,involving functional modules testing(power supply,current transformer,filter circuit and etc.)and the overall performance testing.The results show that the designed parameters are in accordance with the theoretical analysis,and the prototype performance meets the standard requirements.