Design of phase identification system to support three-phase loading balance of distribution feeders

In this paper, a phase identification system (PIS) is designed to incorporate a fuzzy microprocessor based controller for phase measurement of underground transformers. The proposed fuzzy calibration algorithm used in the controller aims to solve the offset and gain of frequency deviation of the real-time clock, which was generated by a voltage controlled crystal oscillator (VCXO) to maintain the timing lock with respect to the 1 Pulse per Second (1PPS) signal of the global positioning system (GPS) before phase measurement is executed. According to the field test of the PIS design, the phase deviation of the real time clock with embedded VCXO can be improved from 46.27° to 0.98° by applying the fuzzy calibration algorithm. The PIS has been applied for field measurement of underground distribution transformers to identify their phases and correct the corresponding attributes of the Automated Mapping Faulty Management (AM/FM) system in Taipower. By retrieving the information of the line segments and transformers from the AM/FM, the network modeling of distribution feeders is derived to analyze the three-phase unbalance. The rephasing strategy of laterals and distribution transformers has been derived and executed by Taipower engineers. By comparing the phase currents and neutral current of a test feeder before and after rephasing, the three-phase balance of the distribution system can be significantly enhanced with the PIS to identify the phasing of distribution transformers for deriving the rephasing strategy of the distribution feeders.