Abstract: The galloping phenomenon of bundled conductors in an overhead transmission line is complicated by the interaction between the large amplitude vibration of the conductors and the geometrically nonlinear, time-dependent aerodynamic loads.For bundled transmission for of long span, the galloping phenomenon is characterized by large amplitude, low frequency vibration with large global torsional motion Non-linear geometric constraints and non-linear gravitational moments are present as a result of the spacers and galloping control devices. In this paper, a basic dynamic equation for bundled transmission lines in a global coordinate system is developed on the basis of virtual work principle. The non-linear dynamics of spacers and galloping control devices are investigated. A galloping model for dynamic configurations of bundled transmission lines is obtained.The present results lay down the foundation for further Study of the problem.