Search

The awareness of the potential safety risk is paramount in the safe operation of overhead transmission lines. The consequence of safety hazards from touch, step and transferred voltages due to Ground Potential Rise (GPR) cannot be ignored or under-estimated. A CIGRE Technical Brochure [1] has been developed to provide a brief overview of the source of the GPR problems related to ground current from ac line faults to the line grounding systems. The GPR issues are sensitive to the soil resistivity near the tower and to other factors. Any safety risk mitigation may require stringent measures at locations where public access is frequent and to a lesser degree when the access is extremely rare. The GPR mitigation should be designed to ensure any potential hazards be kept to acceptable levels.

CIGRE TB 549 (2013) is an update on previous CIGRE documents on the subject, published in Electra more than three decades ago. Lightning parameters needed in different engineering applications are reviewed. New experimental data, as well as the old data, are evaluated. Additional lightning parameters, previously not considered by CIGRE, are included. Possible geographical and seasonal variations in lightning parameters are examined. Specific applications are considered and recommendations are made.

Two clean live-line tool flashovers in Manitoba at 500-kV line voltage and two recent ones in Saskatchewan at 230 kV during freezing conditions led to extensive laboratory tests to reproduce some of these flashover conditions in a controlled laboratory environment to understand the underlying mechanisms and to assess mitigation measures. This paper improves on the three-dimensional finite element method model developed in our previous study to compute the potential and electric field along and around a fiberglass-reinforced plastic hot-stick in a series of “true” cold fog tests at the UQAC. In the previous study, the simulations were carried out with a dry surface and non-uniform wetting. In simulating the non-uniform wetting conditions, since a non-continuous water film was considered to be on the hot-stick surface, there was no leakage current. However, in the flashover and cold fog tests at the UQAC, leakage current activities were observed between the HV and ground electrodes on the surface of the hot-stick. In the present study, the mathematical equations of the model were modified to allow for the presence of leakage current flowing through a continuous thin layer of ice on the surface of the hot-stick in freezing and cold conditions, as was the case for the flashover incidents experienced in Saskatchewan. The potential and electric field distribution along and around the hot-stick were calculated and compared with those in dry surface conditions.

A transient injection method was used to simultaneously measure the time variation of footing impedance and soil resistivity on a series of 345-kV steel pole towers. For each tower, the ratio of transient resistivity to impedance, giving an effective tower perimeter, reached an asymptote by 500 ns. The soil resistivity estimates were log-normally distributed with natural log standard deviation of 0.63 for this locale. These time-evolved resistivity values are compared with observations based on frequency domain modeling.

This paper presents a novel method to improve simulation of the road salt deposit process on energized high voltage insulators under winter conditions. A pollution generator system prototype was especially designed to produce an external mixing of dry solid contaminants (kaolin powder) with supercooled atomized brine droplets. The formed pollutant particles are transported by air flow, which is produced by a speed variable fan, and then settle on the energized specimen insulator surface which is installed at a specific distance of the pollution generator nozzle. The pollution accumulation process took place inside a climate chamber at −5°C. At the end of each ten-minute exposure, specimen insulators were removed for ESDD measurement according to the IEC 60815 standard. No pre-treatment of the insulator surface is needed and contrary to most of the other contamination methods, it enables study of the rate of increase of ESDD with wind speed and insulator profile under winter conditions. The combined effect of wind speed and dielectrophoretic force was also investigated using a 45-kV ac variable voltage source.

This paper presents an analysis of lightning return strokes to tall structures. The interaction of lightning with a tall structure is modeled using the antenna theory. The finite ground conductivity as well as the buried grounding system of the tall structure are taken into account in the analysis. It is shown that the current waveform, in sections of the tower close to ground, is somewhat affected by a finite ground conductivity. However, for sections further up the tower, it is not significantly influenced. Furthermore, our simulations show that some fine structure associated with current waveforms measured on the Toronto CN tower can be attributed to the finite ground conductivity. It is also shown that the current path down the tower structure is notably subjected to the skin effect. The current distribution along the buried grounding structure of the tower is also presented, illustrating the dispersion effect as a function of the ground conductivity. Finally, the lightning return-stroke generated electric and magnetic fields computed at a distance of 2 km from the tower are presented. It is shown that some late-time subsidiary peaks are smoothed out by the effect of the propagation along a finitely-conducting ground.

Hollow-core composite 230-kV station post insulators have been tested with single-phase short-circuit currents, simulating levels up to 85 kA rms-symmetric current (worst-case offset for an outer phase) in a three- phase system. Acoustic emission measurements indicated that these non-ceramic insulators (NCI) were not damaged by the short-circuit tests. Finite-element modelling of the insulator-bus system provided a good description of the tests. The finite-element modelling was used to calibrate a simpler model for station design, similar to the models upon which the ANSI/IEEE Standard 605 [ANSI/IEEE, 1984] and the IEC Standard 865 [IEC Standard, 1986; The Mechanical Effects of Short-Circuit Currents, 1996] are based.

In this study, we present an experimental validation of the transmission line representation of an elevated object struck by lightning. The experimental results are obtained using a reduced-scale model and injected signals with narrow pulse widths (down to 500 ps). The validation is performed using a reduced scale structure representing the Toronto CN Tower in Canada. Two models consisting, respectively, of 1-section and 3-section uniform transmission lines were considered for the comparison. It is shown that the 3-section model is able to accurately reproduce the obtained experimental data. The overall agreement between the 1-section model and the experimental results is also satisfactory, at least for the early-time response.