CHANGE OF PROTECTION PRINCIPLE TO AVOID CASCADE TRIPPING IN A SERIES-COMPENSATION, PARALLEL LINE APPLICATION

In order to prevent cascade tripping in case of distance protection directionality loss in an application with capacitors series-compensation, the substitution of the distance protections by differential line protections was carried out. The present paper describes the process of studies that led to deciding the above mentioned change and the tests carried out for qualification of the new selected protections. Due to demand growth, capacitive compensation was increased in 10 % during 2005 in the Argentine System in order to increase transmission capacity. This was implemented in two substations of the corridor that have series-compensation. Prior to implementation, it was deemed necessary to study the behaviour of the protections of the corridor in the new projected scenario. The corridor was simulated in a digital TNA and all line protections were tested. Special attention was paid to the observation of relay directionality measurements in case of external faults. Results showed a case of a distance protection overoperation for a fault in a parallel line. In particular cases, the current analytical tools to estimate protections behaviour are not enough and there is a need to study the internal performance of the protection in the presence of certain faults. In order to determine exactly the cause of a wrong operation or the protections operational limits for a certain application, it was decided to implement a protection algorithm that would be as close a