Research On The Effects Of Geomagnetically-Induced Current (GIC) On HVDC Transmission System

The offset saturation of transformers as a result of the injection of geomagnetically induced current (GIC) induce high magnitude of harmonic-injections to the system, especially of low-order harmonics. These harmonics propagate between the converters with a particular mechanism. Distortion of voltage on ac bus presents when resonance on harmonics of certain orders occurs which should be regarded as a severe threat to the stability of HVDC transmission system. Researches of the differences of harmonics endangered by transformers with different construction under the GIC-caused offset saturation are presented as well as the propagation mechanism of these harmonics. Investigations also being made on the qualifications of the parallel/serial resonance of the ac/dc side of the converter and the 2nd-harmonic instability.Proofs are presented by the simulations made on CIGRE benchmark HVDC transmission system and other equivalent system. Results of the affections of GIC on harmonic-distortion and reactive power demands are obtained. At last, a comparison among the methods of GIC blocking is made, and principles on choosing and optimizing these methods is drawn out.