![]() Also, horizontal movement with wet snow would only increase this overlap. Wet snow circular galloping envelopes for the new 400 kV line would overlap if interphase spacers were not used (see Fig. 11) and support using such a circular galloping envelope. For example, galloping studies on bundled conductors with wet snow in Japan showed large horizontal movement (see Fig. Moreover, wet snow galloping occurs over a wider range of wind conditions. Wind tunnel studies on conductors with glaze ice versus wet snow accretions have shown the wet snow profile to be more aerodynamically unstable and that more wind energy transfers to the conductor. The galloping envelope was also changed to be circular. 10: Maximum galloping amplitude versus span length. 9: Lissajous ellipse calculation.įield observation of galloping for glaze ice covered conductors were used here instead of calculations and predicted peak-to-peak galloping amplitudes of 10 m for the new line (see Fig. Lissajous ellipses can be calculated for conductors with glaze ice in relatively flat, open areas (see Fig. ![]() 7: Field observations on conductor galloping motion with glaze ice. A (galloping) envelope around recorded points has an elliptical shape (see Fig. Plotting movement recorded by multiple photos of galloping conductors with glaze ice shows mostly vertical motion (see Fig. These include reporting format as well as instructions for camera and video recording. Knowledge of galloping conductor movement has come mostly from field observation and utility guidelines on how to observe and record galloping events have been developed. Predicting Movement of Conductor Galloping Shape of conductor ice and snow accretion thereby affects conductor galloping movement. Bundled conductors are especially susceptible in this regard since their high torsional strength prevents accreted snow weight from twisting the conductor to reduce the concentration of the accretion into the sharp leading edge. 6) that is highly unstable aerodynamically. However wind-driven wet snow packed onto the windward sides of conductors forms a hard, tenacious deposit with a sharp leading edge (see Fig. Rime ice does not create a conductor shape susceptible to galloping. 5: Glaze ice on conductor.Įlevated sections of the Beauly-Denny route where galloping occurred in the past on the pre-existing 132 kV line have experienced wet snow and rime ice accretions. Thin layers of glaze ice on a conductor have a rounded shape (see Fig. Glaze ice accreted on overhead conductors is more commonly considered in analysis and testing studies of galloping than are other types of accretion. 4: Shapes of ice accretion on conductors (IEEE ESMOL & TP&C meeting tutorial -2008). 3 Weather conditions & type of accretion. The various possible shapes of ice accretion on galloping conductors were reported in a past survey of Canadian utilities (see Fig. Wet snow accretion is observed when air temperature is between 0☌ and 3☌ and can occur under any wind speed. Glaze ice can be precipitated or formed in-cloud when droplet freezing time is sufficiently long to allow a film of water to form on the accreting surface. Rime ice is in-cloud icing where super-cooled droplets impact and then freeze onto a substrate. The types of ice and snow that can accrete on overhead conductors are rime ice, glaze ice, frost, dry snow and wet snow (see Fig. Driving wind can vary between 8 to 72 km/h (5 to 45 mph) at a 10 to 90 degree angle to the line and can be unsteady in velocity or direction. Amplitudes are mainly vertical and typically range from +0.1 to 1.0 times the sag of the span while frequencies usually range from 0.15 to 1.0 Hz. In most cases, there is an ice accretion on the conductor that modifies its normal cross-sectional shape such that it becomes aerodynamically unstable. ![]() Galloping is large amplitude, low frequency, wind-induced oscillation of overhead lines. Conductor Galloping Under Wind, Ice & Snow 2: Interphase spacers installed on new line. 1: Route of 400 kV line from Beauly Substation to Denny North Substation in Scotland. A decision was made to also install similar interphase spacers on the two-bundle phase conductors of the new 400 kV line to ensure reliability of this key link in the Scottish and Southern Energy (SSE) Grid Systems.įig. Composite type interphase spacers had already been installed on the 132 kV line to mitigate galloping under these severe weather conditions. The line, running from Beauly Substation to Denny North Substation in Scotland, follows a similar route to an existing 132 kV line and traverses some 220 km of hilly terrain exposed to high winds with wet snow accumulations on conductors during freezing of from 75 to 100 mm diameter. This edited contribution to INMR by Stephen Bell of K-Line Insulators in Canada reports on application of interphase spacers on a 400 kV overhead line built to transmit power from increased renewables generation. ![]()
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