State Grid Corporation of China (SGCC) is the largest power grid in China and includes more than 20 provincial grids. Liaoning Power Grid is just one of them with numerous heavy industry loads. The Donganshan 220kV substation, located in Liaoning province, is a typical substation feeding both heavy industry plants and normal residential areas with the needed electric power.

Those heavy industry loads vary randomly all day long, and cause large voltage fluctuations, as observed in the 24h voltage curves illustrated above. The difference between the highest and lowest voltage within a day can reach up to 10% of the nominal voltage, which caused problems in the adjacent residential areas.

Based on a mutual system study with SGCC, it was proposed that a 66kV directly connected SVC would successfully solve the voltage problem. A SVC capacity was finally designed as 140Mvar with TCR, FC and existing MSC branches that were controlled by a common C&P system. This project resulted in the Donganshan SVC valve becoming the first 66kV thyristor valves in China.

The TCR thyristor valves were based on L TT thyristors and designed as a vertical layout with a water/air cooling method. Redundant circulating pumps and redundant control & protection systems were designed to achieve a high stability and easy maintenance. A SVC major control algorithm was designed as a constant voltage strategy to maintain a stable voltage at the 66kV busbar.

Donganshan’s SVC had been commissioned in 2009. SGCC measured and compared the 24h voltages at both 220kV and 66kV busbars at the substation, which shows the SVC had successfully solved the voltage fluctuation problem. Adjacent residential areas do not need to suffer from the unstable voltage supply any longer.