The Study Of The Impact Of Transformer DC Bias On Micro-computer Protection

Geomagnetic induced currents (GIC) or a high-voltage DC transmission grounding into the earth current flows through the transformer will cause DC bias magnetic saturation, resulting in excitation current distortion, producing harmonics, reactive changes, which will affect the correct action of the relay and threaten the safe operation of the power system. Based on PSCAD/EMTDC and MATLAB software research the transformer DC bias of the harmonic and reactive power characteristics, obtained the corresponding changes in the laws and characteristics, and as a basis for analysis and assessment of the DC bias on the impact of protection devices, combined with microprocessor-based protection principle and algorithm, the DC bias excitation harmonics on the impact of characteristics of digital protection is reviewed and finally with the Northwest 750KV planning power grid in 2010 as an example, simulated and analysed the Possible impacts of microprocessor-based transformers differential protection in DC bias magnetic according to the level of the assessed value of GIC.