Run the simulation and observe waveforms on the main variables scope block. Line current is used for synchronisation, rather than line voltage, since the TCSC voltage can vary widely during the operation. The firing circuit uses three single-phase PLL units for synchronisation with the line current. The controller gain scheduling compensates for the gain changes in the system, caused by the variations in the impedance. Each controller further includes an adaptive control loop to improve performance over a wide operating range. The capacitive mode also employs a phase lead compensator. The reference impedance indirectly determines the power level, although an automatic power control mode could also be introduced.Ī separate PI controller is used in each operating mode. When TCSC operates in the constant impedance mode it uses voltage and current feedback for calculating the TCSC impedance. A constant firing angle can also be applied and the same limits will apply as above. The inductive mode reduces power transfer over the line. In the inductive operating mode, the range of impedances is 19-60 Ohm, which corresponds to 100-85 MW range of power transfer level. The inductive mode corresponds to the firing angles 0-49deg, and the lowest impedance is at 0deg. To change the operating mode (inductive/capacitive/manual) use the toggle switch in the control block dialog. Comparing with the power transfer of 110 MW with an uncompensated line, TCSC enables significant improvement in power transfer level. This range corresponds to approximately 490-830MW power transfer range (100%-110% compensation). In capacitive mode the range for impedance values is approximately 120-136 Ohm. The impedance is lowest at 90deg, and therefore power transfer increases as the firing angle is reduced. The capacitive mode is achieved with firing angles 69-90deg. Note that the resonance for the overall system (when the line impedance is included) is around 67deg.
Since the resonance for this TCSC is around 58deg firing angle, the operation is prohibited in firing angle range 49deg - 69deg. The TCSC can operate in capacitive or inductive mode, although the latter is rarely used in practice. The natural oscillatory frequency of the TCSC is 163Hz, which is 2.7 times the fundamental frequency.
using only the capacitors (firing angle of 90deg). The TCSC consists of a fixed capacitor and a parallel Thyristor Controlled Reactor (TCR) in each phase. Without the TCSC the power transfer is around 110MW, as seen during the first 0.5s of the simulation when the TCSC is bypassed. A TCSC is placed on a 500kV, long transmission line, to improve power transfer.
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