Digital Substation Small Current Grounding Fault Line Selection Program Design

The low current grounding is widely used in 3 ~ 66k V electricpower grids in China. And more than 80% of the earth faults are caused by single-phase grounding. Researchers have proposed a variety of fault feeder selection methods in the past many years, and all the methodologies are based on the simplified model system to find fault characteristics and then to identify fault feeder selection criterion. At present, many principles and algorithms have been used in business, and hardware devices or software packages have been running in different substations. However, the correctness rate is still not high enough and the result is very dissatisfied yet. Some of the higher correctness rate is realized by the high cost of the device. In recent years, with the electric power system reform, the electricity power grid has been developing very rapidly. With the help of computer technology and communication network technology development, substation automation technology has been in a new stage. Digital substation has been a hot concept for several years, and gradually more and more digital substations are being built. In a digital substation, the analogue and binary inputs from the primary side and the control out from the secondary side are very different from that of a traditional substation automation system. The medium, mode and final accuracy of the data transmission are all improved very much. At present, there have been numerous operating digital substations both in China and other countries. The new-style protection relays, monitoring and control devices and lEDs have entered the stage of practical application at the same time. Then, the new-type device for single-phase earth fault feeder selection to be used in a digital substation is inevitable also. A digital substation has more advantages than a traditional substation so that higher correctness rat for earth fault line selection can be achieved more easily. This paper will describe the realization of selecting the single phase earth fault feeder in a Digital Substation.