Protection relaying scheme based on fault reactance operation type

The theories of operation of existing relays are roughly divided into two types: the current differential type based on Kirchhoff's first law and the impedance type based on Kirchhoff's second law. We can use Kirchhoff's laws to rigorously formulate fault phenomena, so the circuit equations are represented as nonlinear simultaneous equations whose variables are the fault point k and the fault resistance R f . This method has two defects: (1) a heavy computational burden in iterative calculation by the N‐R method and (2) the relay operator cannot easily understand the principle of numerical matrix operation. The new protection relay principles proposed in this paper focus on the fact that the reactance component at the fault point is close to zero. The reactances X f ( S ) and X f ( R ) at the ends of the branch are calculated by solution of linear equations. If the signs of X f ( S ) and X f ( R ) are not the same, it can be inferred that the fault point is located in the branch. This reactance X f corresponds to the difference in branch reactance between the actual fault point and an imaginary fault point. Thus, the relay engineer can understand the fault location in terms of the concept of “distance.” Simulation results using this new method indicate that it can provide much more precise estimation of fault locations than those obtained by inspection of operating transmission lines. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 168(1): 29–40, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20720