Researching On Designing The Arc Fault Circuit Interrupters(AFCI)

AFCI (Arc Fault Circuit Interrupter) is a device intended to protect the circuit against the arc fault that may cause fire. When there is an arc fault, the scale of fault current is lower than the initialization of most of the protection devices installed in the lowers, hence AFCI technique is an effective means to detect the arc fault successfully and interrupt the circuit in time.Based on the existing technology background, our research includes establishing the platform of arcing experiment, designing the hardware system of AFCI and writing the software system. Our work focuses on developing the AFCI for single-phase-and-low-voltage 220V/AC distribution systems, which can achieve the automatic detection of arc fault and leakage current fault to protect the conductors and the equipments and ensure human's safety.This paper provides the development background, the lately study work and the foreground of the AFCI technology, then illustrates the characteristics of arc, how it ignites, and what loss it may cause, shows the basic structure of AFCI and the primary principles with that AFCI detect arc fault.Secondly all the research works on this project are introduced, including the platform of arcing experiment, hardware system and software.The platform of arcing experiment is composed of the arc fault generator and the current monitoring and saving unit, and several load appliances, then recommends the experimental process and the instruct of the equipments. The purpose of arcing experiments is to gain considerable arcing current data and establish a data-base as to look for the arc fault characteristics.The hardware of this project is a typical embedded system. The CPU employed is a MCU of 51 series. A switching mode power supply module provides the power to the digital control circuit. Then the paper illustrates the signal input module, the signal amplification module, A/D conversion circuit and the trip implement device. The software is programmed with language C under the Wave 6000 circumstance, which applies the C compiler of Keil C. The whole segment is constituted by the following parts: data sampling, the function of average current calculation, the Fast Fourier Transformation function, the arc detection function, the function of arc characteristic vector calculation, of which the last three parts are the most important.Finally, it is carried through that the modeling and detection of arcing fault for lower-voltage power system, which demonstrates that the algorithm of the arc characteristic vector is feasible. Then the paper summarizes the measures to improve the project and describes the prospect of the AFCI.