Transformer core dc magnetic biasing the cause of the problem

Transformer core dc magnetic biasing the cause of the problem - 2019 03 - 30 15:05:21 dc bias refers to the transformer core excitation current of dc component, lead to magnetic saturation transformer iron core and a half weeks, and the resulting series of electromagnetic effect. Normal work in ac excitation transformer core, iron core magnetic flux density increases, the field current to produce distortion, transformer core work in the area of nonlinear magnetization curve, excitation current waveform is fastigium wave, and the positive and negative half wave is symmetrical, transformer core under dc bias, dc and ac magnetic flux superposition, the same as that of dc bias of the half cycle of iron core saturation degree increase, another half cycle of the saturation degree is reduced, the corresponding field current waveform in asymmetry of positive and negative half wave shape. Single-phase half-wave controlled rectifier circuit and waveform diagram dc bias of transformer core is a kind of abnormal working status, because the original side of the transformer core equivalent impedance of dc component shows only resistance, and resistance is very small. Therefore, small dc component will have large dc excitation in the winding magnetic potential, the dc magnetic potential with ac magnetic potential function in the transformer core original edge, cause in the magnetization curve of the transformer core work shift, appear about the asymmetry of the origin, the bias of transformer. Different causes of transformer dc bias, mainly including dc monopole earth return operation and geomagnetic field disturbance. Unipolar pulse magnetization typical hysteresis loop of dc transmission system in a highly symmetrical or unipolar runtime, there will be some direct current flow through dc system grounding into the earth, ranging from the earth surface potential at the same time, the dc current may be through the transformer neutral point into the iron core transformer, formed in the iron core transformer dc current, the magnetic field of a transformer core secret working point offset, make the transformer core produces dc bias, which cause serious damage to the safe operation of power system. At present, guangdong power grid, jiangsu power grid, guizhou power grid and ningxia grid practical operation experience shows that into the ground current of dc power transmission project has adverse effects on the regional power grid safe operation.