Development of intelligent generator special protection system (iG-SPS) to improve transient stability in dangjin power plants

Unintended loss of the bulk 765kV transmission lines with 4,000 MW generation capacity, which will be increased to 6,000 MW in the near future, will be absolutely a severe situation that can cause total loss of the generation out from it due to generators' over-speed. The Dangjin power plant with eight 500 MW generation units is connected to the Shin-Seosan substation through the double 765kV lines on a tower delivering bulk power to Seoul Metropolitan area. Stable operation of the plant during the loss of the connected transmission line with faults is utmost important for the entire power system reliability. Until now, the generation trip for special protection system (SPS) has been decided by the off-line studies based on the highly stressed system condition only assuming the yearly peak load in Korea. Therefore, an intelligent SPS for Dangjin station to trip the optimal number of generators when faults occur on the connected 765kV lines considering the system operating condition is urgently required. In order to prevent intensive swings and loss of plant synchronism with such severe disturbances on the 765 kV transmission lines exiting from the Dangjin plant, an adaptive SPS has been developing since 2010. The iG-SPS for the Dangjin plant has been developing to optimally minimize the number of generators to be tripped for Dangjin thermal power plant when faults occur on the outlet 765kV transmission lines. As predicting the destabilizing conditions during the credible contigencies using on-line transient stability assessment, optimal numer of generation units to be tripped can be obtained beforehand and armed for the SPS in the Dangjin station. When three-phase faults really occur on the both of the 765kV transmission line, it will be cleared within 5 cycles after the faults by the differential relay protection. Detecting the lines opening, the intelligent SPS will now find matching condition from the look-up table priori prepared with the online stability assessment considering the total amount of the generation produced from plants sharing the double circuited 765kV lines. The several features of the iG-SPS developing in the Dangjin plant are as follows: - Applying periodical on-line transient stability assessement with EMS data - Preparing patching matrix for optimal number of generation trip required - Considering the total generation in the plant and fault location as well as system load condition - Using the PMU measurement data for fault locating - Calculating acceleration power for additional trip when required in real time.