As for such issue as inflexible graded interval classification and threshold setting of traditional power quality and difficulty in reflecting the appeal of different early warning objects to the sensitivity and difference of power quality

a kind of graded early warning threshold setting method of power quality considering the data clustering features is proposed. Firstly

the clustering method is introduced to make clustering classification of each early warning object and to take arithmetic mean value of each power quality index of the same type of early warning object as individual early limit value of the object on the basis of analyzing systematically China national power quality standard and grade classification of traditional power quality

so to exploit and reflect deeply the individual requirement of each early warning object to the power quality;Then

power quality grade interval and threshold value is set as 6 cases based on different situation in accordance with the relations between individual early warning value and international limit of each type of early warning object and each grade interval of traditional power quality

which avoids effectively such circumstance as missing and frequent alarm due to inappropriate setting of each threshold value;Finally

the power quality grade early warning of 20 pieces of 10 k V common connection points for certain power supply bureau is taken as an example to verify the flexible adjustability and wide applicability of the method.