The Challenges in a Case of Protecting a Series Compensated Transmission Line

The more common and economic way for increasing the power transfer capability of a transmission line is by installing capacitor banks that are connected in series with those lines. In such case, the transmission line is called a series compensated line. In general, all of electric components in AC power networks should have their own protection schemes, for instance the transmission lines are protected using the line current differential scheme or the communication aided distance scheme as a primary protection scheme, and in addition a conventional distance scheme (Modified impedance or Quadrilateral protective element) is used as a backup protection. So, installing capacitor banks in series with such lines will raise new challenges to the existent protection scheme of that line. This paper addresses these challenges when a series compensated transmission system needs to be protected from the AC faults or severed disturbances. Where, the most common challenges in series compensated transmission systems are: voltage inversion, current inversion, and sub-harmonic frequency oscillations. A chosen series compensated transmission system will be used as a model for performing this research study, and simulated results will be shown for this work. Finally, based on protection engineer point view the recommendations of the relay settings will be discussed to overcome most of these raised challenges in protecting the series compensated transmission system.