Prediction and control of transient stability using system integrity protection schemes

Prediction of the transient stability in real-time can be a boon in preventing the occurrence of catastrophic events in a particular area that could potentially affect the entire grid and cause blackouts. Synchronised voltage angle measurements procured from the installed phasor measurement units in the network have been used to devise an index for assessment of transient stability in the system. The behaviour of the trend of the acceleration at the instant of the critical clearing angle has been used in this study as the basis for differentiating between a stable and an unstable power swing. Upon detection of an unstable condition, the generator, which is most likely to be going out of step is detected, and appropriate control action is suggested for mitigating the predicted out of step condition. Moreover, the distance relay maloperations caused during a stable power swing can also be a reason for triggering cascading outages. Suitable remedial measures to avoid such maloperations of the distance relay have been proposed. The efficacy of the proposed philosophy has been tested on a single machine infinite bus system, WSCC-9 bus system and New England 39 bus system modelled in Power Factory/DIgSILENT.