Abstract: The necessity of developing a high open curcuit voltage AC arc welder with dou-ble protection system against electric strike has been discussed and the essential techni-cal properties of the welder have been proposed in this paper.The three technical characteristics-welding voltage,current setting range,and open curcuit voltage,which are the main technical bases for designing the welder,have been analysed and their numerical values given.The working principle of the device has also been analysed thoroughly.To ensure that the device will function effectively,the idea of double-protection was first introduced and a satisfactory device of such was developed.