A New Method and Instrument for Ground Impedance Measurements

This paper describes the hardware, software, and testing procedures using the smart ground meter, developed under EPRI sponsorship. The functions of the meter are discussed and examples of recent nieasurements are presented using a prototype unit. The instrument injects a transient electric current between the ground under measurement and an auxiliary ground, and it measures ground pokntial differences (GPDs) around the ground under measurement. 'I'he GI'D measurements are processed with software which rejects external noise using correlation methods. Subsequently, estimation methods are used to extract thc ground potential rise and ground impedance. 'I'he final result is the ground inipedance versus frequency in a user selected frequency range. The data collected with the smart ground meter can be utilized for a number of applications, such as estimation of maximum ground potential rise, touch and step voltage measurements, soil resistivity evaluation, etc.