Description

In this example, a Thyristor Controlled Series Capacitor (TCSC) is connected to a 500kV long transmission line (simulated as a series R-L correspond to approximately 500 km), to improve power transfer [1], [2].

Without the TCSC operating, the power transfer is around 110MW. The nominal compensation is 75% impedance i.e. compensates for 75% of the total line inductance when only using the series capacitors, with the firing angle (alpha) kept at 90˚. The natural oscillatory frequency of the TCSC in this example is 136Hz, which is 2.7 times the fundamental frequency. 

The TCSC can operate in capacitive or inductive mode. Since the resonance of the TCSC occurs around alpha equals 58˚ and the resonance of the overall system occurs around 67˚ in this example, the controllers are limited to operate outside of the 49˚ < alpha < 69˚ region: 

• The capacitive mode operates in the 69˚ ≤ alpha ≤ 90˚ region
• The inductive mode operates in the 0˚ ≤ alpha ≤ 49˚ region

The manual fixed alpha angle mode is also available.

Location

This example model can be found in the software under the category "FACTS & HVDC" with the file name "TCSC.ecf".

Simulation and Results

For the first 0.5 s, the TCSC is bypassed using the circuit breaker. As can be seen from the results, during the first 0.5 s of the simulation when the TCSC is bypassed, the power transfer is around 110 MW. At 0.5 s, the TCSC begins to regulate the impedance to 128 ohm. It should be noted that the PI controller is made fast to display the results in 5 s. The power transfer is increased to around 610 MW. At 2.5 s, a 5 % change in the reference impedance is applied that validates the TCSC can change its impedance according to the setting of reference value. At 3.3 s, a 4 % reduction in the source voltage is applied, followed by the return to 1 pu at 3.8 s. The TCSC impedance is maintained to its reference value.

References

[1] D.Jovcic, G.N.Pillai "Analytical Modelling of TCSC Dynamics" IEEE® Transactions on Power Delivery, vol 20, Issue 2, April 2005, pp. 1097-1104.

[2] https://www.mathworks.com/help/physmod/sps/examples/tcsc-detailed-model.html