Short-term Reliability Online Evaluation Basing On Transient State Probability

The reliability of the power system in a future short term is studied according to the current state. Basing on this, we can alarm and prevent the outage to assure the safety and reliability of the power system. Traditional reliability is an expected value of long-term reliability level under the fixed operating mode, which cannot reflect the real time reliability level under the current operational state. This essay presents the novel conception and algorithm of online evaluating the short-term reliability in order to study the operational reliability level. The influence of the variable system states on the reliability level is reflected according to the real time operational information provided by the SCADA/EMS/WAMS. Markov process is adopted to solve the transient state probability of the components, so that forecasting the system state basing on the transient probability is possible. The probability of the system state and the reliability indices of the system changes as the time varying. The analysis and the assessment of IEEE RTS-79 system indicates that there are great differences between the short-term and long-term reliability indices, and only the transient probability evaluation can assess the short-term probability properly. In this paper the relationship between the enumerating number of the system states and the forecasting time is also studied. The result indicates that only a few system states are needed to get relative high degree of evaluation accuracy, which can be applied online. IEEE RTS-79 case study is calculated to verify this conclusion.