An Accurate Model of Multi-Type Overcurrent Protective Devices Using Eigensystem Realization Algorithm and Practice Applications

  • Cheng, Chao-Yuan ;
  • Wu, Feng-Jih
  • Received : 2013.07.10
  • Accepted : 2015.08.26
  • Published : 2016.01.01


Accurate models of the characteristics of typical inverse-time overcurrent (OC) protective devices play an important role in the protective coordination schemes. This paper presents a novel approach to determine the OC protective device parameters. The approach is based on the Eigensystem Realization Algorithm which generates a state space model to fit the characteristics of OC protective devices. Instead of the conventional characteristic curves, the dynamic state space model gives a more exact fit of the OC protective device characteristics. This paper demonstrates the feasibility of decomposing the characteristic curve into smooth components and oscillation components. 19 characteristic curves from 13 typical and 6 non-typical OC protective devices are chosen for curve-fitting. The numbers of fitting components required are determined by the maximum absolute values of errors for the fitted equation. All fitted equations are replaced by a versatile equation for the characteristics of OC protective devices which represents the characteristic model of a novel flexible OC relay, which in turn may be applied to improve the OC coordination problems in the sub-transmission and distribution systems.


Curve fitting;Eigensystem realization algorithm;Novel flexible overcurrent relay;Multifunction equation;Overcurrent protective device


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