Field observation of galloping on four-bundled conductors and verification of countermeasure effect of loose spacers

This paper describes the galloping occurrence conditions of four-bundled conductors and the galloping suppression effect of diagonally arranged loose spacers, which is a type of spacer applicable for four-bundled conductors with two rotational clamps placed at diagonal positions. Field observations were conducted at a full-scale test line in Japan where in-cloud icing frequently occurs. A total of 40 ice accretion events were observed across four winter seasons, and galloping data were obtained in a non-countermeasure phase set with normal spacers and a countermeasure phase set with loose spacers. The relationship between the total displacement amplitude and tension variation was determined to identify the conditions under which large galloping occurred based on tension data, in addition to the displacement data. Galloping was found to occur at wind speeds exceeding 9 m/s, and large galloping oscillations were observed when a certain relationship was satisfied between the wind speed and the amount of ice accretion. Furthermore, it was observed that the loose spacers reduced the galloping oscillation amplitude by approximately 40%. The rotational clamps operated normally under severe natural conditions, and the suppression effect was caused by the difference in the ice accretion characteristics of the rotatable subconductors owing to their rotation. •Field observations in a full-scale test line at a site of in-cloud icing.•Oscillation amplitude and tension were measured on four-bundled conductor lines.•Galloping occurred at a wind speed over 9 m/s with a certain amount of icing.•Loose spacers reduced the galloping oscillation amplitude by approximately 40%.•Differences in ice accretion among the rotatable subconductors suppress galloping.