| Fuzzy theory considered as a burgeoning subject is applied in many fields of power system,so much as in protective relay field. After analyzing the basic principle of fuzzy theory and its application in power system protection relay, this paper presents novel technique for fault phase selection in EHV power system based on transient protection theory. Wavelet transform is proposed to extract the high frequency signals and correlation analysis is applied to the results. When different types of fault occurred, the feature of the high frequency signals has different similar relations. By analyzing the characteristics of faults, a series of new principles are preferred base on fuzzy set. A new scheme applying fuzzy set theory to the single-pole adaptive reclosure is proposed. Then the fuzzy measures and memberships of a series of new criterions such as magnitude, phase and power are proposed. It uses the fuzzy set synthetically to distinguish permanent fault and instant one occurred on EHV lines. This paper will try to discuss all kinds of hardware platforms realizing the fuzzy protective relay, in which CPLD/FPGA act as peripheral fetch chip, special digital processor and system-on-chip mode. This paper will also propose a novel mode which CPLD controls DSP.
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