Assessing the dynamic stability of the Slovenian power system

Slovenian transmission system operator detect how close to dynamic instability the power system is at any given moment. Essential to the tool is the dynamic model used for dynamic simulations. The model comprises a detailed representation of the high-voltage Slovenian power system and a simplified model of the surrounding network, where certain approximations were introduced both to accelerate the dynamic calculations and to compensate for missing data. For real-time application, the dynamic model is automatically configured using the setpoints from the energy management system, and the adequacy of the resulting steady-state conditions is verified by comparing the models power flow results with SCADA measurements.

Upon sufficient matching, several dynamic simulations are launched, where the response of the dynamic model to most severe contingencies is observed. Transient stability is assessed by simulating three-phase faults and their clearance by tripping the affected line, frequency stability is evaluated by simulating single generator outages and monitoring the frequency response of the remaining units, and small signal stability is examined by computing the systems oscillatory modes using QR decomposition. Because the simulation outputs are too extensive to present in full time series form, only the most critical information is extracted and provided to the user, whereas more detailed results are available upon request: for transient stability, the critical clearing time of each contingency, for frequency stability, the minimum/maximum frequency, maximum absolute rate of change of frequency and frequency margin and for small signal stability, the relative damping of the oscillatory modes. The developed tool can also be applied for offline analysis such as system operation planning or the statistical security assessment of past operation states. In this paper, we present a use case in which the analysis of historical recordings indicated near critical conditions. The underlying causes of the situation are examined, and possible remedial actions are proposed highlighting the practical value and applicability of the tool.