Research On The Test System For Breaking Capacity Of A Fuse

A fuse breaking capacity testing system was designed in this paper.The test system has two AC power supplies,namely low-voltage AC power supply and high-voltage AC power supply.The former provides breaking current of the fuse and the other provides the rated voltage of the fuse when the fuse is broken,which can detect the arc extinguishing capability of fuse and prevent the fault expand.Compared with the typical circuit recommended by the national standard,the impact on the power grid and the power consumption of the current limiting resistor are greatly reduced by using this system.It solves the problem of the two power supply fast switching perfectly by using the high-speed opto-coupler and micro-controller interrupt.Constant current source is designed for accurate determination of the main circuit resistance,the main circuit resistance and low voltage AC power supply together determine the breaking current of the fuse.The main contents of this thesis are as follows:1)The design of zero-crossing circuit,the thyristor can turn on within ±100 range by selecting the appropriate voltage to ensure the safety of thyristor and prevent interference to the network.Reasonably select current limiting resistor value of opto-coupler to make the one work in the safe range.2)The design of synthetic circuit,by using two AC powers,low-voltage AC power supply provides current of the fuse before the fuse is broken,otherwise,in typical circuit breaking current is determined by limiting resistor,it greatly increase unnecessary power consumption of the resistor,at the same time high-voltage AC power supply can provides the rated voltage after the fuse is broken,which meets the national standard test requirements.The synthetic circuit can reduce the capacity requirements of the grid and current limiting resistor power consumption greatly.3)The design of linear constant current source which ensures the accurate measurement of loop resistance.4)The testing system adopts the principle of ergonomics in mechanism design,which is convenient for testing and personal safety.