State Grid Corporation of China (SGCC) is the largest power grid utility company in China, managing more than 20 provincial power grids. Among them, Liaoning Power Grid serves a high concentration of heavy industrial loads. Donganshan 220kV substation, located in Liaoning Province, is a typical substation that supplies power to both large-scale industrial plants and residential areas.

Those heavy industrial loads at this site fluctuate significantly throughout the day, causing severe voltage instability. As shown in the 24-hour voltage curves, the daily voltage fluctuations can reach up to 10% of the nominal voltage. These fluctuations not only affected industrial efficiency but also caused persistent power quality issues for residents in the surrounding areas.

Through a collaborative study with SGCC, a 66kV directly-connected SVC was identified as the optimal solution for the voltage instability. The system was designed with a capacity of 140Mvar, integrating TCR , FC and existing MSC units that were controlled by a common C&P system. This project had made the Donganshan SVC valve become the first 66kV thyristor valves in China.

The TCR thyristor valves were based on LTT thyristors and feature a space-efficient vertical layout with a water/air cooling method. To ensure high reliability and simplified maintenance, the design includes redundant circulating pumps and a redundant control & protection system. The SVC major control algorithm was designed as constant voltage strategy, ensuring the 66kV busbar maintains a stable and consistent voltage level.

Since its commissioning in 2009, the Donganshan SVC has delivered exceptional performance. Post-installation measurements by SGCC at both the 220kV and 66kV busbars confirmed that the SVC successfully eliminated the previous voltage fluctuation problem. As a result, the adjacent residential communities now enjoy a reliable and stable power supply, ending the long-standing challenges caused by industrial load interference.