Calculation and measurement of the earth impedance of an e.h.v. substation

Fault currents in extra-high-voltage transmission systems have increased in recent years, and in view of the necessity to keep ground potentials to a minimum, greater accuracy and assurance is required in determining the impedance between substations and the general body of earth. The paper describes tests carried out at Amersham 400 kV substation using injected alternating current and other established methods. The results of these tests are compared with previously calculated values, and conclusions regarding the accuracy and suitability of the various methods are presented.