In this master’s thesis, we simulate the operation of the Slovenian power system, with emphasis on the transmission network and active power flows on heavily loaded critical interconnections. We focus on the Divača–Redipuglia line, where bottlenecks often occur due to Slovenia’s transit position and the large import of electricity into Italy. A phase-shifting transformer (PST) at the Divača transmission substation is currently used to regulate power flows on this line, and the thesis evaluates whether it would be worthwhile to replace it with the more advanced static synchronous series compensator (SSSC) device. SSSC belongs to the family of flexible AC transmission systems (FACTS) devices and enables faster and more precise regulation of active power flows.
The thesis first addresses the structure of the Slovenian power grid and the importance of power flow analysis for reliable system operation. It presents network losses that can be reduced using flow control devices. The operating principles of PST and SSSC are described in detail. PST regulates power flows by means of phase shifting; it operates discretely and therefore has limited precision. SSSC changes the effective line reactance by injecting a controlled voltage, enabling better control of active power flows in transmission lines. In addition, SSSC offers better system adaptability, lower internal losses, and is more suitable for modern grids with a high share of renewable energy sources.
To assess the performance of both devices, a simplified network model was developed in Python. The Newton–Raphson method was used for power flow calculations, while the interior point method and particle swarm optimization were used to optimize the operation of both devices. The analysis was carried out under different operating conditions by varying load, line flows, and an N‑1 contingency scenario. The results show that using SSSC leads to lower system losses and better flow regulation closer to the target value.
The final part of the thesis determines the economic viability of replacing the PST with an SSSC. The results depend on which factors are included. If only loss-related savings are considered, the investment is not economically justified. However, when additional SSSC benefits such as increased cross-border transfer capacity, higher reliability, and improved dynamic performance are taken into account, the installation of an SSSC becomes a sensible solution. The final conclusion is that replacing the PST with an SSSC is technically superior and economically justified when broader system benefits and the strategic importance of future network development are considered.
|
