The invention relates to a method of restricting the
direct current magnetic bias to generate the
noise of the
transformer, which belongs to the emergency protection circuit device field. The invention comprises a stopping direct unit and a primary
system fault protection unit, the invention is characterized in that two electrolytic capacitances with polarities are connected in series in an inverted polarity way, and a
diode is in parallel connected at the both ends of each electrolytic
capacitance in a reverted polarity way, so as to form a stopping direct unit; at least more than two diodes are connected in series in sequence in an identical direction way, so as to form an unidirectional
overvoltage protection circuit, and two unidirectional
overvoltage protection circuits are connected in parallel in a reverse direction way, so as to form a complete primary
system fault protective unit. The continuity of the grounding circuit is guaranteed during the changing process of the grounding current at the whole central point from small to large, the complex controlling circuit and the
thyristor element are avoided, no risk of the stopping
direct component is guaranteed by a built-in auto bypass, the structure parameter of the prior
electric network is not changed, and simultaneously, the
direct current component can be completely partitioned during the normal operation.