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Stability and Transient Study

Stability and Transient Study

The ability of a power system, containing two or more synchronous machines, to continue to operate after a change occurs on the system is a measure of its stability. The stability problem takes two forms: steady-state and transient. Steady-state stability may be defined as the ability of a power system to maintain synchronism between machines within the system following relatively slow load changes. Transient stability is the ability of the system to remain in synchronism under transient conditions, i.e., faults, switching operations, etc. 

In an industrial power system, stability may involve the power company system and one or more in-plant generators or synchronous motors. Contingencies, such as load rejection, sudden loss of a generator or utility tie, starting of large motors or faults (and their duration), have a direct impact on system stability. Load-shedding schemes and critical fault-clearing times can be determined in order to select the proper settings for protective relays. 

A simulation will include synchronous generator models with their controls, i.e., voltage regulators, excitation systems, and governors. Motors are sometimes represented by their dynamic characteristics as are static var compensators and protective relays. 

Compliance: The stability study will be performed in accordance with the recommended practices and procedures set forth in ANSI/IEEE 399 and following NETA recommendations. 

Study Report: Following NETA recommendations, the results of the stability study shall be summarized in a final report containing the following items: 

  • Basis, description, purpose, and scope of the study.


  • Tabulations of the data used to model the system components and a corresponding one line diagram.


  • Descriptions of the scenarios evaluated and tabulations or graphs showing the calculation results.


  • Conclusions and recommendations.