In the present paper a comparative performance of the SVS auxiliary controllers for the dynamic performance enhancement of long transmission lines with and without series compensation has been evaluated. A new controller, namely, combined reactive power and frequency (CRPF) auxiliary controller has been developed and incorporated in the SVS control system located at the middle of the transmission line. The proposed SVS auxiliary controllers, considerably, enhances the system damping and the unstable system modes are stablized. A digital computer simulation study, using a nonlinear system model, has been performed to illustrate the performance of the proposed controller.