PMU applications in the Korean Power system: Wide-area monitoring and control (WAMAC) system

In the paper, the study on the development of wide-area monitoring and control (WAMAC) system applied to Special Protection Scheme (SPS) to mitigate voltage instability in KEPCO system is introduced. Based on EMS and synchro-phasor data, the new two-step load shedding scheme is developed to be able to replace the current single-step scheme. The developed WAMAC system contains this control function as a remedial action scheme as well as advanced human-computer interfaces for intuitively situational awareness of Seoul metropolitan area in the Korean Power system. The purpose of the WAMAC system, which is installed in real field, is to help system operators to keep their systems more stable under unexpected events of Korean power systems through the realtime visualization representing current system status and time-synchronized, highly-sampled data acquisition from PMUs installed in the system. Synchro-phasor data from 40 PMUs installed on 28 substations over 345kV voltage levels in Seoul metropolitan area are used for the purpose. The best places for PMUs to get the maximum observability of the system are optimally selected based on analytical and heuristic methods simultaneously. The WAMAC system in Korea has a hierarchical structure which consists of three levels. The first level is PMUs on the basement for the measurement of system data. The PMUs with IEC61850 being supported can measure synchro-phasor data as well as control the power system with GOOSE message. The second is the data acquisition level from PMU data to PDCs (Phasor Data Concentrators) for RCC(Regional Control Centre), where each system collects and analyzes the PMU data for its own purpose. The last is the highest operation and monitoring level for the Global Control Centre, where the WAMAC system has monitoring and assessment function of the power system in real-time. The idea for the main control function in the WAMAC system is started from the real-time index, which can represent system stability very dynamically and exactly. The WAMAC system uses WAVI(Wide Area Voltage stability Index) and dynamic FV(Flow-Voltage) curves as the index for the new load shedding scheme with two steps. At the first step, it sheds in the same way as with previous methods but only the amount of change to about 1,000MW. In the majority of power system cases, it does not need second step load shedding. At the second step, after the first load shedding, it monitors the Seoul metropolitan area using the 40 PMUs very precisely. If the system crosses over the thresholds such like (of) voltage, interface flow and voltage stability index, the system performs the second step load shedding for the remaining 500MW.