The paper presents a comparative performance evaluation of SVS auxiliary controllers for transient stability enhancement of long transmission lines over a wide operating range. The SVS has been considered located at the middle of the transmission line. The application of the auxiliary controllers considerably enhances the system damping and unstable system modes are stabilized. A new controller, namely Combined Reactive Power and Frequency (C.R.P.F.) auxiliary controller, has been developed for the SVS located at the middle of the transmission line. To illustrate the comparative effectiveness of the auxiliary controllers under disturbance condition, a digital computer simulation study has been performed. © 1996 Taylor & Francis.