Method for detecting topological structure of grounding grid under extremely cold condition

The invention relates to a grounding grid topological structure detection method under an extremely cold condition, which comprises the following steps of: in a substation in an extremely cold region, determining a measurement region S on the ground surface of a grounding grid according to positions of grounding grid branches and nodes in a selected region, acquiring dynamic current values of the branch nodes through a current sensor based on TMR (Tunnel Magnetoresistance), and calculating the topological structure of the grounding grid according to the dynamic current values; then the magnetic induction intensity of the measurement area S is indirectly obtained through conversion, and the magnetic induction intensity comprises the magnetic induction intensity Bz (x, y) perpendicular to the ground surface direction and the magnetic induction intensity By (x, y) parallel to the ground surface direction; calculating a model of a first-order derivative and a model of a third-order derivative of the magnetic indu