COMPORTAMIENTO DE LA PROTECCIÓN DE DISTANCIA EN LÍNEAS DE TRANSMISIÓN EQUIPADAS CON TCSC.

Abstract

The conventional way to increase the transmission capacity of a power system is to build new transmission lines of electricity. This task is now virtually impossible to achieve mainly due to the difficulties of obtaining new rights of way which are limited by both economic and ecological reasons. An alternative way to increase power transmission capacity is using FACTS (flexible AC transmission systems) that allow controlled reactive power compensation. In particular, controlled series compensation improves the transmission line capacity by electrically reducing very long transmission lines (i.e. reducing transmission angle) by means of thyristor-controlled series capacitors (TCSC). Distance relays which commonly protect in an adequate way overhead transmission lines, now are affected by the new dynamic introduced by TCSC when this device is installed in transmission line for compensation purposes. Under ideal conditions, a differential protection scheme could be the better way to reduce the incorrect operation of relays, however, sometimes this is not possible to implement due to economic reasons or due to the unavailability of the appropriate communication channel. Due to this, the study of this problem is necessary such that a methodology can be proposed to improve the performance of distance relays when operating in this compensated transmission line. In order to solve this problem a controlled series compensated transmission line is simulated in an electromagnetic transients program EMTDC. This line includes a TCSC and distance relay models. The TCSC is placed in the middle of one line while the distance relays are installed in every line end to achieve a total of six relays in the test power system. A large number of fault cases were simulated and the resulting impedance values measured at each relay were recorded in text files through the use of a Matlab interface. Once all data representing impedance of relays from fault scenarios is recorded this data is analyzed in an Excel spreadsheet in which the main logic of distance relays is implemented. In this way, the total number of correct and incorrect relay operations was obtained. The simulation cases were incorrect operations occurred were classified according to the severity degree in the power system. Thus once the problems are classified, a methodology is proposed to reduce number of incorrect operations. The proposed methodology is based on a channel communication protection scheme that uses directional comparison unblocking signals (DCUB). Quadrilateral characteristic with extended resistive reach is in distance relays instead of conventional mho shape. By using the proposed scheme and according to results, the total number of incorrect operations of distance relays is drastically reduced in the power system equipped with TCSC.