Research On DC Bias Of Power Transformer

More and more DC bias is ouccred on traditional AC transformers, due to the applications of geomagnetically induced current caused by solar activities and HVDC unipolar operation mode, the core of transformer will be saturationed when the DC current increases to a certain extent, that will lead to the increase of transformer noise, vibration and heat, Injected a large number of harmonics into the grid, affect the correct operation of protection devices and reduce the system voltage etc. Therefore, the study of DC bias and its suppression measures have a great practical significance and long-term strategic significance.In this paper, the mechanism of DC bias have been analyzed first, and then discuss some adverse effects on transformers and the power system caused by DC bias, after that an example of transient electromagnetic field of single-phase transformer has been established using finite element analysis software Maxwell 2D, and then use this model to analyze and compare the internal magnetic field changes in core and yoke under different DC current.Based on the Unified Magnetic Equivalent Circuit(UMEC) model of transformer, the excitation current and its harmonic of DC biased power transformer have been analyzed by using PSCAD/EMTDC in this paper. The tolerance abilities of Single-phase, three-phase three column and three phase five column transformer under DC bias have been compared. Finally,some common suppression measures for DC bias of transformer have been discussed, and analyzed the suppression measure of the feasibility and validity of self-excited compensation method and applied DC compensating power supply method, using the simulation model constructed with PSCAD/EMTDC.The final conclusion is: the leakage flux gradually increased with the saturation of the core, that will lead to the increase of vortex in the position where the leakage flux flows. And the highest point of the calorific appears in the the junction of yoke and core and the junction of yoke and yoke. The order of the tolerance to DC bias of different core structure is:three-phase three limb transformer, three-phase five limb transformer and single-phase transformer. The suppression measure of self-excited compensation method and applied DCcompensating power supply method can effectively inhibit the DC Bias...