Voltage sag seriously impacts the safety of industrial enterprise such as chemical industry, metallurgy, etc. Existing governance for voltage sag mainly adopts electrical equipment measures, the ideal way is to research voltage sag itself. The impact of voltage sag on electrical equipment can be decreased to minimum by rapidly removing faults or putting into standby power. Reducing the influence of voltage sag by using rapid removal of fault, this paper develops a rapid protection program for identifying the fault by jointly using change rate and absolute value of current sampling value before and after fault. In order to improve the accuracy of fault identification, the DC component of the normal operation should be eliminated before determination. Simulation shows the fast protection scheme is able to quickly and accurately determine any type of fault in power system and makes relay operate after fault occurred 5 ms.