China Southern Grid (CSG) is the second largest grid in China operating both high voltage AC and DC transmission lines. The main loads are located at the east section, with major generators 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’s 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.

The power needs from the east were consistently increasing every year, leading to the existing corridors facing more pressure in their transmission capability. CSG had to do its best to enhance their power transmission limits.

According to a system study, an SVC rated 210Mvar at Wuzhou substation will improve the situation. The Guangxi - Guangdong corridor’s transmission limit will increase by 100MW while Yunnan - Guangdong corridor by 30MW and Guizhou - Guangdong corridor also increases by 30MW. So theoretically an extra 160MW power flow will be obtained with an SVC in operation. The dynamic voltage stability can also be improved by this SVC when there are any line faults occurred nearby.

A SVC of 210Mvar was designed and delivered by RXPE for CSG Wuzhou 500kV substation in 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 a 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. A control & protection system were also designed as fully redundant.

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. 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.