| Summary: | 碩士 === 國立臺北科技大學 === 電機工程系 === 107 === The single-phase pole transformer of the power distribution system is generally used for supplying low-voltage users. It always outage by a fault caused by lightning, which is close relationship with the lightning and fault characteristics and the insulation coordination and protection coordination of a transformer. It is necessary to further discuss for proposing an improved strategy. In this thesis, the lightning and fault characteristics of an existent single-phase pole transformer are analyzed considering different installation positions of main protection devices (arrester and current-limiting fuse) under different lightning strike points and lightning strength. In addition, the transformer is fed by phase and neutral conductors from a three-phase four-wire (3Φ4W) distribution system with a multi-grounded neutral line. The influence of different grounding resistance levels of each neutral grounding point is also discussed. Furthermore, the defects of the existent protection coordination and insulation coordinationon of the single-phase pole transformer are evaluated, and the improved strategy is proposed for upgrading protection performance of the transformer and the reliability of power feeding. First of all, the Alternative Transient Program of Electromagnetic Transient Program (EMTP/ATP) is used for modelling and simulating a system under normal operation, lightning, and ground fault situations, respectively. Based on the EMTP/ATP simulation results, the voltages and currents of transformers, arresters and current limiting fuses are further surveyed. Furthermore, the Basic Impulse Insulation Level (BIL) and current damage curve of the transformer are comparied with the protection characteristic curves of arrester and fuse, and the setting of protection relay on an upstream substation to evaluate the disadvantage of insulation coordination and protection coordination. Finally, the improved strategy will be proposed to upgrade the protection performance as well as improve the reliability and safety of power feeding for users.
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