Method for measuring ground impedance of large grounding grid

The invention discloses a method for measuring the ground impedance of a large grounding grid, and relates to the technical field of the measurement of grounding characteristics of large grounding grids such as grounding grids in power stations or transformer substations. Based on the phase difference measurement of a reference vector of test current, module values and phase difference of an outlet overhead ground wire and a power cable outer sheath of a power station or a transformer substation to shunts of the test current are obtained; and through a vector of each shunt and calculation, the actual diffused current vector of the test current passing the grounding grid is accurately solved, so that the ground impedance of the grounding grid is accurately measured. According to the conventional method for measuring the ground impedance of the grounding grid under the condition that the running power station or transformer substation is provided with an outlet ground wire, the shunts of the overhead ground wire and the cable outer sheath are not measured, or the vector of each shunt is only measured, the phase difference from the vector of the test current is not measured, a result that the shunt module value is subtracted from the test current is only obtained, and the simple treatment method is changed. The accuracy for measuring the ground impedance is improved, serious systematic errors are avoided, and the state of the grounding grid is accurately evaluated.