Long-distance power transmission

SVC is able to improve transmission and distribution performance of the power system remarkably. SVC should be installed at one or several proper points in the grid in order to achieve the following purposes:

• Stabilize voltage of a weak system
• Reduce the transmission losses
• Enhance transmission capacity and make existing grid most efficient
• Improve transient stability
• Increase the resistance in the small interference
• Enhance the voltage control and stability
• Mitigate the power oscillation

Substation(66/11kV)

Rongxin SVC may make quick and precise capacitive and inductive reactive compensation,which will stabilize the bus voltage and increase its power factor and also solve reactive power releasing problem completely.Furthermore,when new SVC is installed,the original fixed capacitor bank may also be fully utilized,and only TCR is required.SVC may reach the optimum effect with minimum investment,and it has becom the most effective method for improving power quality of the regional grid.

The SVC used in the power system, especially the ones in transmission network, is normally in TCR+TSC+FC structure, as described below:

                  Typical TCR+TSC+FC SVC project of Rongxin

Single-line diagram of TCR+TSC+FC 

Customer Needs
China Southern Grid (CSG) is the second biggest grid in China operating both high voltage AC and DC transmission lines. The main loads are located at its east part of the grids however the major generators are located at the west. Both 500kV AC corridors and 500kV / 800kV HVDC corridors are used to transmit the needed electric power from west to east. Wuzhou 500kV substation is an important node in the middle of these corridors to receive power flow from both AC and DC transmission lines coming from the west.

• Black Lines     AC Transmission lines
• Blue Lines       DC Transmission lines
• Green Circle    Wuzhou 500kV Substation

RXPE Solution
A SVC of 210Mvar was designed and delivered by RXPE for CSG Wuzhou 500kV substation in the year 2008. The SVC includes one TCR branch and two harmonic filter branches as well as two MSC branches, output capacity from -120Mvar inductive to +210Mvar capacitive. The MV busbar was designed as 35kV that is connected to 500kV busbar by a dedicated step down transformer.

The thyristor valves were designed as horizontal layout with water/air cooling method. Three circulating pumps had been applied in the cooling system to further improve its overall reliability and availability. Control & protection system were also designed as fully redundant.

Customer Benefits
Wuzhou SVC had successfully achieved its design targets. It enabled the CSG dispatching center to increase the transmission power flow of these corridors from west to east. Meanwhile it has also increased the voltage stability of the adjacent network. On June 5th 2009, the substation 500kV bus voltage dropped rapidly due to a line fault. The SVC acted to support the line voltage and helped the grid successfully ride through the incident, which also verified its dynamic performance.