Distributed Control of Compensation Devices for Enhancing Stability of Long-distance AC Transmission System

Steady-state and transient stability of longdistance AC transmission system has been substantially improved by implementing distributed control of reactive power compensation devices. Transfer capability could be enlarged for more than 25% by increasing voltage at intermediate substations and synchronous condenser capacity installed in the middle of line. Analysis of small-signal stability shows that application of WAMS data in static VAR compensator and synchronous condenser control systems leads to increase in transmitted power limit up to 10 GW. Moreover, distributed control of static reactive power compensation devices allows to overcome the special property of long line and provide the operating conditions with angles of more than 180 degrees. The experience of transient stability calculations of ultra-long AC transmission line is presented. It is noted that transmission system is unstable without implementing additional countermeasures. When using series electrical braking in combination with high-speed turbine control, transient stability could be ensured.