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<p>Technique to evaluate probability of occurrence of selected contingencies of 6 Bus Roy Billinton Test System (RBTS) and IEEE 9 Bus system by Markov modelling is presented in this paper. Obtained probabilities for selected contingencies are validated by comparing with binomial distribution based probabilities. Load flow analysis and performance index based contingency ranking of total elements of 6 bus RBTS and IEEE 9 Bus systems is simulated by Power System Simulation for Engineers (PSSE) software. Novel reliability evaluation technique which unify contingency ranking with Markov modeling is proposed for RBTS and extended to IEEE 9 Bus system. Accuracy, completeness and simple to implement are salient features of proposed novel reliability evaluation method. Reliability of RBTS and IEEE 9 Bus systems can be improved by incorporating Flexible Alternating Current Transmission Systems (FACTS) device. Improvement in the reliability and economic revenue of RBTS and IEEE 9 Bus systems due to Unified Power Flow Controller (UPFC) incorporation is evaluated.</p>

Together with quality power supply criteria, Composite Power System (CPS) reliability is also one of the important aspects of deciding the security of the CPS for a given load demand. In the current paper, the reliability of CPS is evaluated. The Newton Raphson (NR) approach is implemented in Power System Simulation for Engineering (PSSE) software to take into account, the load flows, then the power available to the load points, to evaluate the reliability of CPS. Newton Raphson NR Method was implemented by considering different contingencies of the CPS. Power available to the load points obtained by the NR method is critical in identifying the successful operating state of the CPS. Expected Load Curtailment (ELC), Number of Load Curtailment (NLC), Expected Energy Not Supplied (EENS), and Severity Index (SI) are the crucial dependability indices that are assessed. The main objective of the Reliability evaluation of the CPS is to investigate the scope for the improvement of reliability and explore the possible schemes to improve CPS reliability. The Unified Power Flow Controller (UPFC) one of the Flexible AC Transmission Systems is incorporated into the CPS to analyze the improvement in the reliability of the system. Further, the effect of UPFC on the power-carrying capacity of the lines under contingency conditions, resulting in the failure mode of CPS operation is examined. Improvement in the reliability indices of the system is observed due to UPFC incorporation.

The effectiveness and reliability of the unified power flow controller (UPFC) are determined by the insulated gate bipolar transistor (IGBT) valve. Thermal losses, conduction losses, and switching losses in the IGBT valve all affect the efficiency of UPFC. The failure rate of the converter valves is influenced by junction temperature, which has an impact on the converter's reliability. Piecewise linear electrical circuit simulation (PLECS) was used to simulate two IGBT valve-based converter legs working at 12000 Hz, part number GT30F123. By reference to the switching characteristics produced by PLECS, switching losses, conduction losses, and thermal losses are analyzed. Simulation results are corroborated with analytical measurements. The chance of achieving 100%, 50%, and 0% functioning modes are among the reliability indices that are analyzed. The chance of achieving a hundred percent, fifty percent, or zero percent functioning mode is assessed. The frequency of achieving the state probability and mean time to failures (MTTF) are obtained from probabilities using the Markov model. The thermal losses, failure rate, and lifetime of the UPFC are all quantified to give a complete picture of the UPFC's performance.