| Summary: | 博士 === 國立臺灣大學 === 電機工程學研究所 === 90 === This dissertation presents synchronized phasor measurement technique and its applications to transmission line digital protection. The scope of protection includes two-terminal and T-type transmission lines. In order to eliminate the error caused by exponential decaying DC offset on the computation of fundamental and harmonic phasors, an extended Discrete Fourior Transform is also proposed. For two-terminal lines, the functions of protection include fault detection, fault location and distinguishing between arc fault and permanent faults. The fault detection on two-terminal lines is achieved by combination of fault detection index |M| and fault location index |D|. One is to detect the occurrence of fault, and the other is to distinguish between in-zone and out-of-zone faults. Extensive computer simulation studies show that the average response time of fault detection is about 8 ms and the least fault location error is about 3 m (0.003%) for 100 km transmission lines. The discrimination between arc fault and permanent faults is achieved by arc voltage estimation by virtue of harmonic phasors caused by the fault arc. Computer simulations also show that the proposed algorithm can correctly estimate the arc voltage to distinguish between the arc fault and permanent fault. Utilizing the measured synchronized phasors on three ends of T-type lines, a fault detection technique using composite differential current method combined with a zone decision algorithm is proposed. It speed up the response time of fault detection. For fault location on T-type lines, a two-step algorithm is proposed. The first is to identify the fault section by virtue of applying the pseudo fault location index into the fault section identification criterion. The second is to reduce T-type lines into two-terminal lines containing the fault. Thus, fault location technique for two-terminal lines can be applied to locate the fault. Extensive computer simulations have shown that the fault location errors are only 5 m around for the best case and well within 400 m in all of the computer simulation studies.
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