Microcomputer-based differential protection of generator-transformerblock of Jingnan Hydroelectric Power Plant

The design on microcomputer-based longitudinal differential protection of generator-transformer block in Jingnan Hydroelectric Power Plant is introduced. The principle of longitudinal differential protection is the comparison of current amplitude and phase between the sides of generator and/or transformer. The relay will actuate while there is a fault within the range of protection, due to the relay input current equals to the sum of the short-circuit current from two sides. The protection system is composed of the following four parts: input/output interface converter, processor module, output unit and control panel. The flow of protection includes three steps: signal input, signal control and processing and signal output. The software can realize the functions of microcomputer-based protection in accordance to the sequences listed below. Firstly, the input parameters on behalf of the current phase difference and unbalanced current between the two sides are preprocessed. Secondly, they are transferred as balanced current criteria of the two sides and then are judged successively by the differential principle. Finally, the trip order will be sent out to the trip matrix with the actuation conditions of longitudinal differential protection.