Investigation of effect of galloping countermeasures for four-bundled conductors through field observations

The application of a galloping countermeasure device is one of the main approaches to suppressing galloping and maintaining a stable electricity supply. Loose spacers are a galloping countermeasure for four-bundled conductors that are normally installed in Japan. Loose spacers have two rigid clamps and two rotatable clamps, in contrast to normal-line spacers, which have four rigid clamps. This is expected to suppress galloping by changing the aerodynamic characteristics of the conductors. There are two types of loose spacers: diagonal and one-sided. The former has two rotatable clamps facing each other diagonally. In the latter case, the two rotatable clamps are installed in the upwind side. The galloping-suppression effect of diagonal loose spacers has been demonstrated in previous field observations. Additionally, previous wind tunnel tests proved that one-sided loose spacers are superior to diagonal loose spacers. However, the galloping-suppression effect of one-sided loose spacers and their difference from diagonal loose spacers should be investigated using wind tunnel tests and field observations. In this study, the effectiveness of a one-sided loose spacer and its differences from a diagonal loose spacer were investigated through field observations of four-bundled conductors over eight winter periods. The results showed that one-sided loose spacers were superior to diagonal loose spacers because the maximum tension fluctuation of the conductor with one-sided loose spacers was smaller than that with diagonal loose spacers. However, the galloping of conductors with one-sided loose spacers still occurs in certain situations. Typical galloping is observed when the wind speed is relatively high and the rotational angle of the conductor bundle is relatively large. In this case, the effect of one-sided loose spacers seemed insufficient because the rotational angle of the rotatable clamps was smaller than 80 degrees, which is the limit angle of the equipment.