Synchronised data-based adaptive backup protection for series compensated line

Metal oxide varistor (MOV) protected series capacitor, when present in a fault loop, modulates the impedance seen by the relay. With series capacitor placed away from the relay, the information on the level of compensation is required for proper protection decision by distance relay. In this study, synchronised data obtained at both ends are applied to calculate the compensation level which is used to adapt the relay setting for backup protection of adjacent line. The mutual coupling in the compensation portion is also considered in the apparent impedance computation. The status of capacitor during fault (bypassed or not) is obtained through impedance calculation during fault and the relay setting is adapted accordingly. Using data simulated through EMTDC/PSCAD for a series compensated line the technique is tested and found to be accurate.