Thesis
COMPORTAMIENTO DE LA PROTECCIÓN DE DISTANCIA EN LÍNEAS DE TRANSMISIÓN EQUIPADAS CON TCSC.
Autor
ESCALONA REYES, MAURICIO
Institución
Resumen
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.