Coherency in Power Systems

  • Robin Podmore
Part of the Power Electronics and Power Systems book series (PEPS, volume 94)


There has been a continuing need over the past several decades to model larger and larger interconnection wide models. Models of the complete interconnections with up to 50,000 buses are regularly used for system planning studies. These models typically go down to 115 and 69 kV levels, but ignore underlying 35 kV sub-transmission networks. With the growing deployment of plug-in vehicles, distributed generation and smart load controls, along with the need to perform realistic system restoration drills there is a need to model interconnections down to the feeder breaker level. Restoration drills also require modeling of power plant auxiliaries and emergency generator systems, especially for nuclear units. It is conceivable that the size of interconnection wide models could grow by another order of magnitude. The EPRI DYNRED (Dynamic Reduction) computer program reduces a large-scale system model into a smaller equivalent model for use in transient stability studies. The program has been used since the 1970s to build equivalent models of the Eastern U.S. and Western U.S. interconnected power systems. The DYNRED program accepts a normal transient stability database as input, and develops an equivalent that is a fraction of the size of the full power system representation, while adequately retaining the dynamic characteristics of the full system. The reduction process requires only a fraction of the time needed for a transient stability simulation.


Synchronous Machine Transient Stability Nonlinear Load Coherent Group Equivalent Network 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


  1. 1.
    R.W. deMello, R. Podmore, K.N. Stanton, Coherency-Based Dynamic Equivalents: Applications in Transient Stability Studies, in PICA Conference Proceedings (1975) pp. 23–31Google Scholar
  2. 2.
    R. Podmore and A. Germond, “Dynamic Equivalents for Transient Stability Studies”, Systems Control, Inc., Final Report prepared for EPRI Project RP-763, April 1977Google Scholar
  3. 3.
    R. Podmore, Identification of coherent generators for dynamic equivalents. IEEE Trans. Power Apparatus Syst. PAS–97(4), 1344–1354 (1978)CrossRefGoogle Scholar
  4. 4.
    A. Germond, R. Podmore, Dynamic Aggregation of Generating Unit Models, in Proceedings of IEEE Winter Power Meeting ( N.Y , New York, January 1977)Google Scholar
  5. 5.
    D. Hackett, Coherency Based Dynamic Equivalent Application Experience - Eastern US Data Bases, in PICA Conference Proceedings 1979Google Scholar
  6. 6.
    H.W. Dommel, N. Sato, Fast Transient Stability Solutions. IEEE Trans. Power Apparatus Syst. PAS–91, 1643–1650 (1972)CrossRefGoogle Scholar
  7. 7.
    B. Stott, O. Alsac, Fast decoupled power flow. IEEE Trans. Power Apparatus Syst. PAS–93(3), 859–869 (1974)CrossRefGoogle Scholar
  8. 8.
    J.B. Ward, Equivalent circuits for power-flow studies. AIEE Trans. 68, 373–382 (1949)Google Scholar
  9. 9.
    W.F. Tinney, W.L. Powell, N.M. Peterson, Sparsity-Oriented Network Reduction in PICA Conference Proceedings (Minneapolis, 1973), pp. 384–390Google Scholar
  10. 10.
    W.F. Tinney, J.W. Walker, Direct Solutions of Sparse Network Equations by Optimally Ordered Triangular Factorization. in Proceedings of IEEE 55 (1967) pp. 1801–1809Google Scholar

Copyright information

© Springer Science+Business Media New York 2013

Authors and Affiliations

  1. 1.IncSysBellevueUSA

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