Key Techniques Of Area-protection Based Feeder Automation

Feeder automation (FA) plays an important role in improving the reliability of power systems. The existing techniques are intelligent switches based FA and computer-communication-network based FA. The former needs the switches to re-close several times, thus it impulses the power equipments seriously. The latter needs transmitting fault information to main station, which telecontrols the corresponding switches to isolate fault sections after determination, therefore the restoration procedure lasts a long time and it depends on the reliability of so many elements as well.A new scheme of area-protection based FA is proposed in this paper. Each Feeder Terminal Unit (FTU) enduring a fault current sends a lock order to its up-stream FTU and a trip order to its down-stream FTU, respectively. The decision is made by each FTU according to its overload information and the message from its adjacent FTUs to isolate a fault within the smallest range and to avoid over-tripping. The FTU on loop switches decide whether to close the corresponding loop switches for restoration on the basis of no-voltage detection, settings of delay time and the message from the adjacent FTUs. Based on the proposed methodology, not only can faults be isolated rapidly, but also the impulse to power equipments due to many times of reclosing can be reduced. The proposed scheme doesn't need to transmit fault information to main station as well. Besides, the scheme is also suitable to a distribution network with tapped branches.The design of terminal units for area-protection, basic principle of fault isolation and restoration, the approach for grid with tapped branches, the communication protocol and its realization are described. The restoration speed and the influence on FA due to communication malfunction are analyzed.The area-protection function is realized by assembler language on the platform of FTUs based on 80C196KC microprocessor.