The effect of decarburization on the fatigue life of overhead line hardware

Altering the microstructure in order to improve the tensile properties of bow shackles resulted in inconsistency in the fatigue performance. This raises the question whether the inconsistency in fatigue life can be attributed to microstructural changes along the profile of the shackle or to decarburization at the surface. Bow shackles forged from 080M40 (EN8) material were subjected to different heat treatments in order to alter the microstructure. The shackles were subjected to five different fatigue load cases, which represented typical loads experienced at termination points for an overhead power line with a span length of 400 m, with changes in conductor type, configuration, wind, and ice loading. Although the change in microstructure does improve both the tensile and fatigue performance, we found that the depth of the decarburization layer has a greater effect on the high cycle fatigue life of bow shackles than the non-homogeneous microstructure.

Support Structures for Seal Switches Located Near Bus Lines

The authors propose three designs for seal switch support structures located near power plant bus lines. The first one has a plate that is attached to bus lines located in the same plane. The second uses a support insulator as the case and can be attached to several bus lines at the same time or each of them individually to provide a wide application range. The third design stipulates seal switch installation on overhead line pylons. The authors provide detailed descriptions of the designs and explain how the trip settings are adjusted on them.

Determination of Electromagnetic Influence of 25 kV AC Electric Traction Network on 10 kV High-Voltage Overhead Line

Electrified railways include a system of cable and overhead lines. An analysis of the operation of alternating current (AC) electrified railways sections shows that the value of the induced voltage caused by the operation of the traction network can significantly exceed the permissible level on adjacent disconnected high-voltage overhead lines. As a consequence, this leads to serious injuries to operating personnel, including deaths, failure of electrical equipment. From this point of view, 1x25 kV 50 Hz AC railway system networks are considered the most dangerous. The electromagnetic influence of the traction network of a double-track section of an AC railway on an adjacent 10 kV high-voltage overhead line for power supply of automatic block signalling is investigated in the offered paper. Emergency cases of traction network operation are considered: short-circuit situation and forced state. The calculations of short-circuit currents in the influencing inter-substation zone, as well as estimation of the induced voltage on the wires of the 10 kV disconnected high-voltage overhead line for various schemes of grounding, have been performed. The investigations were carried out on models built using the ATP-EMTP program.

Selection of parameters of overhead lines models when calculating transient processes during earth faults in 6–10 kV networks

Single phase-to-ground faults are the most common type of faults in 6–10 kV overhead distribution networks. Arc intermittent single phase-to-ground fault (PSP) are the most dangerous for the network and the damaged element. They are followed by intense transient processes and, as a result, dangerous overvoltage rate and significant transient current surges at the point of insulation damage. PSP transients also have a significant effect on the selectivity and operation stability of protection devices against this type of damage. Therefore, the development of the methods and means to improve the operation efficiency of 6–10 kV overhead networks in case of PSP and technical improvement of protection devices in many cases is due to the need to calculate the transient processes that occur during insulation breakdowns of the network phase to earth. For the systems under consideration, the reliability of transient processes calculations in case of PSP is determined mainly by the accuracy of estimation of the parameters of 6–10 kV overhead lines, first of all, of inductance, which generally depends on the frequency of the transient current components. In the scientific papers devoted to the study of transient processes in case of PSP in medium voltage electrical networks, including 6–10 kV overhead networks, constant (frequency independent) values of inductance are used as a rule in the equivalent circuits and in the models of transmission lines. An urgent task is to estimate errors caused by the application of this approach to determine the parameters of 6–10 kV overhead lines during the calculations and modeling of transient processes during PSP, and cases of its application. Advanced methods of modeling of electric power systems and their elements have been applied with the use of COMSOL Multiphysics and PSCAD software to obtain the frequency dependences of the inductances of a 6–10 kV three-phase overhead line and study of their influence on the calculation accuracy of transient currents and voltages in case of PSP. The parameters of 6–10 kV overhead line models developed in the indicated software packages at a frequency of 50 Hz are set in accordance with the reference data. The authors obtain the errors estimation to determine the parameters of transient currents and voltages during PSP in 6–10 kV overhead networks when using transmission line models. The frequency dependences of inductance, which are up to 40–50 % in amplitude are not considered. The results show that application of frequency-independent models is permissible only in the cases when parameters of the calculated equivalent circuit of the network and position of PSP point remain practically constant, when solving problems that require high accuracy to determine the parameters of transient currents and voltages, for example, to determine remotely the location of a ground fault, it is necessary to use frequency-dependent models of 6–10 kV overhead lines. Introduction of the developed recommendations to determine 6–10 kV three-phase overhead lines parameters allow us to increase the reliability of calculations and to avoid raw errors when solving the problems which are related to the study of transient processes in case of earth faults in the networks of the given voltage class.