Objective: Persistent strong aeolian vibrations in recent years have caused multiple conductor and strand breakages, as well as hardware wear and failure, across long-span and standard-span transmission lines throughout northwestern, northern, and northeastern China. To address the limitations of existing vibration dampers, specifically their suboptimal damping characteristics and restricted protection spans, this study develops an optimized design that effectively mitigates these fatigue risks. By enhancing the aeolian-vibration resistance of transmission lines, this approach protects conductors and fittings, thereby extending their service lives. Methods: A nonlinear energy sink method was used to optimize traditional vibration-damper designs, after which the vibration-mitigation performances of engineering prototypes were experimentally verified and theoretically evaluated. First, a theoretical nonlinear coupling model was established to analyze the vertical coupling vibration between the conductor and the nonlinear-stiffness damper, incorporating the damping, mass, and cubic stiffness of the oscillator. Next, nonlinear dynamic methods were used to decouple and solve the model. Thereafter, the numerical relationship between the displacement function and strain of the conductor and damper oscillator was clarified to maximize the proportion of oscillator vibration energy to the total energy of the coupled system. Based on this design, three critical coefficients were optimized and selected: the mass, nonlinear stiffness, and damping of the oscillator system. Results: The theoretical analysis indicated that the impact of the mass factor of the vibration-isolation device (oscillator) on the maximum dynamic bending strain of the conductor was negligible under low-intensity aeolian vibration. Conversely, the stiffness factor significantly impacted performance, necessitating rigorous analysis and optimization before structural design in transmission engineering. Furthermore, enhancing the damping characteristics was essential for effective vibration mitigation. Second, following authoritative industry testing standards, engineering prototypes of the nonlinear-stiffness damper were designed and customized using a 140 m experimental line as a typical example and experimental object. Comparative experiments were conducted to evaluate key performance indicators, including power characteristics and protection spans, thereby validating the optimization principles of the nonlinear stiffness and damping parameters. The related indicators, such as resonance frequency dispersion, maximum peak-to-valley ratio, and the effective damping frequency range, satisfied all standard engineering requirements, demonstrating that the device was suitable for deployment and applications on operational transmission lines. Finally, based on the power characteristics and anti vibration effect evaluation experiments in the existing standards, the data showed that the damping ratio of a single nonlinear-stiffness damper, which was greater than or equal to 1.5, represented a 140.0% increase over traditional FR-type anti-vibration hammers adapted to the same conductor model. Under identical strain-control thresholds, the optimized nonlinear-stiffness damper achieved a maximum protection span of 402 m, compared with 280 m by a traditional damper, representing a significant 43.6% increase. Conclusions: Overall, this study verified the effectiveness and technical advantages of the proposed design, demonstrating that the engineering application of the nonlinear energy sink theory significantly enhances aeolian-vibration resistance for high-voltage transmission lines.