A Single Ended Fault Location Method Using Traveling Wave Natural Frequencies

Travelling wave fault location can be classified into single-ended and double-ended methods according to different ways of obtaining the fault information. Double-ended method does not depend on multiple reflections of the travelling wave between the station buses, therefore it has higher reliability and accuracy. On the other hand, single-ended method relies on information from one end only. It does not need time synchronization or communication devices, thus more economical. However, the present single-ended methods are less reliable or accurate, which make single-ended travelling wave fault location one of the hottest subjects of research.A new method of accurate fault location using frequency information from one end only is presented, which is different from the traditional analyzing methods based on telegrapher's equations. In this paper the lossy homogeneous transmission lines are described by the multi-port model, and the power systems connected at each ends of the line are represented by lumped circuits. The model is thus composed of transmission lines and lumped circuits. It is then used to derive the transmission line terminal voltages and current functions in Laplace domain. Using the characteristic equations of the terminal voltages or currents functions, the relations of poles of travelling wave, line length and boundary conditions are further derived. On the other hand, the poles of the voltage/current functions are identical to components of the frequency spectra (hereafter referred to as natural frequencies) resulted from frequency transform of the voltage/current signals. Given the line parameters, using adequate frequency estimation methods to obtain any component of travelling wave natural frequencies (normally the dominant component), together with the boundary conditions (power system equivalent reactance), the distance between two terminals which forms the natural frequencies can be accurately calculated. For fault induced travelling wave frequencies (local bus the one end, fault point the other), the length is naturally the fault distance.The relations of fault induced natural frequencies, fault distance and boundary conditions are thoroughly discussed at single phase and three phases, lossless and lossy lines, frequency independent and dependent line parameters. This helps to make the theoretic foundation of the algorithm complete.After that, various aspects of the realization of the new algorithm are discussed:First of all, the realizations of the new algorithm under different fault conditions are studied. Then the modal mixing phenomenon at single-phase-to-ground fault is analyzed. A novel algorithm which improves the accuracy of fault location under the modal mixing conditions is presented and discussed theoretically and through simulations.Different ways of estimating the fault induced travelling wave natural frequencies are discussed. The pros and cons of traditional frequency transform methods, time-frequency transformation and parametric spectral estimation to this particular application are compared and discussed.The effects of different bus configurations on the algorithm are discussed. The change of bus configurations may cause the variation of the shape of the travelling wave and the formation of additional natural frequencies. The new algorithm is immune to the variation of the wave shape, a property which is superior to traditional time-domain method. The formation of additional natural frequencies has an influence on the algorithm. New approaches of identifying the correct wave front are also introduced in this paper. It can be found out that it is still easier in the frequency domain than in the time domain to distinguish the wave reflected by fault point and the remote bus.The effects of transient response of instrument transformers to the algorithm are studied. A new single-ended fault location method using capacitive voltage transformers (CVT) secondary voltages is presented.After all aspects of the theories and realizations of the travelling wave natural frequencies fault location method are taken care of, a large amount of simulations are conducted in order to verify the accuracy of the algorithm.