A Normal Form-Based Power System Out-of-Step Protection: Article No. 107873

Nnaemeka Ugwuanyi, Xavier Kestelyn, Olivier Thomas, Bogdan Marinescu, Bin Wang

Research output: Contribution to journalArticlepeer-review


This paper proposes a new system-level application for monitoring out-of-step (OOS) events in power systems. As already known, amplitude-dependent frequency shift is a nonlinear phenomenon of electromechanical oscillations under large disturbances. The frequency shift indicates the system's nearness to instability. This new tool utilizes the Normal Form method to identify the named phenomenon, leading to accelerated OOS detection. The proposed strategy is illustrated and compared to the equal-area criterion method in a single-machine-infinite-bus power system. Extensive tests on IEEE 3- and IEEE 50-machine power systems prove the efficacy and potential of the proposed method for online warnings of instability and ranking of vulnerable system modes.
Original languageAmerican English
Number of pages11
JournalElectric Power Systems Research
StatePublished - 2022

NREL Publication Number

  • NREL/JA-5C00-80262


  • normal form
  • oscillation frequency drift
  • out-of-step prediction
  • transient stability


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