Reactive power control during power system restoration and HVDC investigation

Abstract: As the society gets more and more dependent on electrical energy, it is highly desirable to ensurepower supply at all times. In case of events of natural disasters, simple technical faults or human mistakes, any power system or a large part of it can suffer a blackout. An electrical shutdown is a crisis situation where recovery should happen as quickly as possible. During the restoration after the blackout in Sweden and Denmark on 23 September 2003, one problem that delayed restoration was reactor hunting. This thesis suggests a method to avoid hunting and decrease the time of restoration. The result consists of an equation, which uses a variable that describes the strength of the net and with this equation new settings for the Extreme Voltage Automatics (EVA) in the system can be calculated. The method is tested through simulations of NORDIC32 in ARISTO. Many restoration sequences are tested and reactor hunting is avoided in all of them. Further investigations on how VSC-HVDC connections can assist in power restoration have been made. The conclusion is that it works and that it also is possible to energize lines. It is shown that a system is less sensitive to voltage fluctuations, when HVDC is used. That means shunt reactors can be used with existing automatics during power restoration with HVDC.