Search

This paper presents an artificial neural network (ANN) based approach to improve the speed of a differential equation based distance relaying algorithm. As the differential equation used for the transmission line protection is valid only at low frequencies the distance relaying algorithm requires a lowpass filter removing frequency components higher than those for relaying. However, the lowpass filter causes the time delay of the components for relaying. Thus, the calculated resistances and reactances do not converge directly to the fault distance even after data window occupies post fault data. Faults with the same fault inception angle have similar shapes of impedance loci. If an ANN is trained with the shape of various impedance loci for fault distances and fault inception angles, it can predict the fault distance with some values of calculated resistances and reactances before they converge to the fault distance. Therefore, the ANN can improve the speed of the distance relaying algorithm without affecting its accuracy. Moreover, the proposed approach can speed up more when a higher sampling rate is employed. The proposed approach was tested in three rates of 24, 48 and 96 samples/cycle (s/c) in a 345 (kV) transmission system and compared with the conventional distance relaying algorithm without ANNs from the speed and accuracy viewpoints. As a result, the approach can improve the speed of the relaying algorithm.

In this paper, a three-dimensional algorithm for the insulation design of the high-voltage equipment is presented. In general, the insulation design consists of two steps. One is the electric field calculation. The other is the correction of the shape of the electrode or the insulator to be designed. The main point of this paper is the introduction of the rational B-spline to improve the shape control for the insulation design. In former researches, the correction of a shape is made by direct control with the nodes on the shape. This required many design variables and causes the discontinuous curvature of a designed shape. These problems can be dealt by the indirect control which is one of the useful properties of the rational B-spline. The use of rational B-spline results in the reduction in the number of design variables and guarantees the smooth curvature of the designed shape. The proposed algorithm is applied to the design of the shape of the shield ring which is installed in the joint of transmission lines and the insulator and has been designed by the method of trial and error. The combination method of Charge Simulation Method(CSM) and surface Charge Simulation Method(SCSM) is used to calculate the three-dimensional electric fields produced by this system. Key Word: Three dimensional algorithm, Insulation design, Combination method, Indirect control, Rational B-spline, Shield ring

For the rather complicated and time-consuming three-dimensional electric field calculation in the vicinity of transmission lines and substations, this paper proposes an effective numerical calculation method based on Charge Simulation Method(CSM). In order to represent non-uniform charge distribution on an electrode better, it is subdivided into small segments with linear charge density. Each segment with linear charge density can be easily represented by a generalized finite line type of charge whose expressions for potential and electric field were analytically derived and which was named 'finite slant line charge' in this paper. As for the arrangement of small segments of a subdivided electrode, it has been found that unequally spaced arrangement method is superior to equally spaced one. In order to arrange segments fast and effectively, effective formulas were derived from multiple regression analysis of many simulations. The proposed method is applied to the electric field calculation around the transmission lines with significant change in direction and substation busbars. keywords - Three Dimensional Electric Field, Finite Slant Line Charge, Unequally Spaced Arrangement, Charge Simulation Method, Transmission Lines, Substation Busbar

Current transformer (CT) saturation may cause relays to malfunction. The conventional method to deal with the problem is overdimensioning of the core so that CTs can carry up to 20 times the rated current without exceeding 10 % ratio correction. However, this not only reduces the sensitivity of relays, but also increases the CT core size. This paper presents a technique of estimating the secondary current corresponding to the CT ratio under CT saturation. The proposed algorithm can improve the sensitivity of relays to low level internal faults, minimize the instability of relays for external faults, and might ultimately assist in reducing the dimension of the required CT core cross section.