Study On Protection Technology Of AC And DC Residual Currents For Micro Circuit Breakers

Micro circuit breaker (MCB) is also called miniature circuit breaker, widely used inindustrial, commercial and residential low-voltage distribution network in order to preventoverload, short circuit, leakage circuit, etc. With the development of smart grid and growingnumber of electrical equipment, when some of the equipment fails, the residual currentgenerated is not just sinusoidal, but also includes high frequency AC component, pulsatingDC component, or even smooth DC component. The traditional circuit breaker can notprevent such a complex AC/DC residual current.On the basis of analysis of several current detection technologies, a kind ofelectromagnetic transformer and magnetic modulation transformers collaborative detectiontechnology for AC/DC residual current detection is introduced. The electromagneticresidual current transformer is used for detecting the AC component of the residual currentand the magnetic modulation residual current transformer is used for detecting the DCcomponent of the residual current, then two signals have been detected. Both they will beamplified and filtered, and finally let them overlay each other with a certain proportion.Thereby it restitutes the AC/DC residual current waveform and achieves the detection ofAC/DC residual current.According to the magnetic properties of magnetic materials, the correspondingelectromagnetic residual current transformer and magnetic modulation residual currenttransformer are designed. In hardware circuit design, including design of low-pass filter,signal detection circuit, adder circuit, tripping circuit and power supply circuit; in softwaredesign, the residual current waveform recognition software is designed, different residualcurrent waveforms correspond to different action thresholds. Finally, an AC/DC residualcurrent circuit breaker prototype is designed.Test on the designed residual current transformer, hardware detection circuit, and theresidual current circuit breaker prototype, including residual current detecting range test,frequency detection range test, output waveform and the circuit breaker operationcharacteristics test, test results coincide with the theoretical analysis.