Self-excitation operating constraint for generators connected to DC lines

In a generating station linked to a main power system through an HVDC transmission line, a load rejection of the HVDC line may cause generators in the station to become self-excited, resulting in a severe system overvoltage. It may also cause damage to generator exciters if negative current is not allowed to flow in the exciter. This paper derives the self-excitation operating constraint for generators operating in such a system. Results show that a self-excitation operating constraint greatly reduces the operating zone of a generator in such a station. However, this operating constraint can be effectively improved by self-excitation protection systems to remove surplus AC filter capacitive VArs.